Increasing knowledge and suggesting new heat treatment parameters for improved very high cycle fatigue (VHCF) strength of austempered ductile iron (ADI) are the main purposes of this thesis. The work was performed within Epiroc a mining and infrastructure company. They have performed internal research on VHCF properties of ADI had previously for one set of heat treatment parameters. The scientific community in contrast have extensively studied fatigue properties of ADI in the low to high cycle regime (≤10⁸ cycles) but only scarcely in the VHCF regime (>10⁸ cycles). Therefor the thesis is built upon the hypothesis: ‘Improvements in HCF strength should also mean improvements in VHCF strength’. Enabling utilization of published research on heat treatment effects on fatigue strength in the HCF regime (≥10⁷ cycles).

Finding an efficient way of exploring heat treatment parameters and their effects on the given Cu-Ni-Mo ADI alloy were a main objective. Thus, finding mechanical- and material properties characteristic for high cycle fatigue strength in the HCF regime became crucial. The potential in using these properties to develop and execute an experimental plan to evaluate heat treatments, yet minimizing the amount of fatigue testing required.

The first step was identifying the heat treatment parameters (and parameter ranges) that showed high HCF strength, which are: Austempering temperature (T_aus), austempering time (t_aus) and austenitization temperature (T_γ). Then finding the characteristic mechanical- and material properties for said high HCF strength material, found to be: high- ductility, unnotched impact energy and volume fraction of carbon stabilized austenite (VRA). With both heat treatment parameters, mechanical- and material properties distinctive of high HCF strength material an experimental plan was developed based on a full factorial design (2³). The factorial design was chosen for its simplicity and inherent strengths, especially as both individual and interaction effects can be estimated for all factors (heat treatment parameters). Two levels (2³), one high and one low, for each of the three factors (2³) were determined necessary, giving a total of 8 heat treatment trials. The primary response variables of interest (evaluated properties) for each heat treatment trial were: ductility, unnotched impact energy and volume fraction of carbon stabilized austenite. Meaning usage of the following tests: Tensile testing, impact energy testing, and X-ray diffraction. Specimens for testing were extracted from austempered Y-block type III, initially cast by a commercial foundry with an Epiroc specified chemical composition. The main and interaction effects from the heat treatment parameters on the response variables were both calculated and visually determined. The experimental data was validated against literature found data for similar heat treatments. The evaluated experimental results showed good correlation with literature for the given chemical composition. Ultimately resulting in recommendations for a new heat treatment parameters for improved high cycle fatigue strength.

High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing. 

Several studies had been performed on accumulative roll bonding (ARB) for AA1050; however, most of them were conducted at room temperature. Here, the ARB process was performed on AA1050 plates through nine cycles at elevated temperature. An innovation introduced a new parameter (UTS×El.ε) to compare the strength-elongation balance between the present study and previous works. Also, as another parameter, the toughness was compared. Comparing these parameters with previous works showed that the considered samples in the present study performed 14 to 63% better than the other samples, so they were more industrially favorable in terms of mechanical behavior and performance. ARB process at elevated temperature may slightly lead to grain growth compared to room/cryogenic temperature, but creates a better elongation, which ultimately leads to a better balance of the strength-elongation parameter. The results showed that the effect of inter-cycle heating was found significant on microstructural evolution and mechanical behavior. Upon five cycles of the process, the grain size was decreased from 35 to 1.8 μm. The yield strength and ultimate strength increased up to 305% and 94%, respectively. Microhardness test showed that warm ARB reduces inhomogeneity factor in the thickness after 3 cycles. Fractography by SEM showed that the sample failed through shear ductile rupture and that the dimples became smaller, more elongated, and shallower onto the failure surface as the number of ARB cycles increased. In short, the warm process is preferred to the cold process to achieve better mechanical performance and toughness.

Magnesium with two-thirds of the density compared to aluminium and one-quarter of steel, intrigues product developers and material scientists due to the light metal’s excellent combination of strength to weight ratio as well as their capability of being produced as a High Pressure Die Cast component compared to other ferrous or light metal alloys.

However, a magnesium alloy inherits some concerning drawbacks, limiting the exploitation in structural applications and mechanical design such as automotive, heavy machinery and aerospace components. The need for a magnesium alloy that could withstand a sufficient amount of wear, temperature and corrosive environment, leads towards the investigation and evaluation of a suitable, functional coating as a solution to exploit the evident advantages a magnesium alloy exhibits. A substantial amount of research is required in order to reduce an existing knowledge gap that is the ongoing development in the search for a sufficient functional coating and adherence capability to the highly reactive substrate that is a magnesium alloy.

This industrial master thesis is an early stage investigation to evaluate how the currently used aluminium substrate with an electrodeposited coating relate and compares to a heat-treated electroless deposited coating through tribological and thermophysical induced stresses. These properties are tested with proven industrial standard methods resulted in a comprehensive conclusion and discussion regarding the feasibility of applying the coating onto a commercial magnesium alloy closely related to the Mg-alloy developed by Husqvarna and thereby contributing to technological advances to the highly relevant topic within product development in materials engineering.

This paper reports the hardness, elastic modulus and refractive index values of the oxynitride glasses prepared from woody biofuel ashes. The glasses were prepared in nitrogen atmosphere at 1350-1500°C with addition of Ca metal as a precursor to the extra addition of this modifier. The glasses were homogenous, but appeared translucent grey to black. They contained up to 23 eq% of Ca and 5 eq% of N. The glass densities vary slightly between 2·76 to 2·92 g/cm3. The molar volume and compactness values vary between 8·01 cm3/mol to 8·31 cm3/mol and 0·446 to 0·462 respectively. Mechanical properties like hardness and reduced elastic modulus show values, up to 10 and 105 GPa, respectively. These properties are strongly correlated with the amount of N in the glass. The refractive index (1·54-1·75) increases with increasing N and Ca contents.

In this work hypoeutectic lamellar graphite iron alloyed with seven different levels of molybdenum was studied in order to characterize its thermal and mechanical properties. Several tests were conducted and experimental data was collected from, laser flash (LFA), differential scanning calorimeter (DSC), dilatometer and tensile test.

Micrographs taken from the polished specimens were captured and studied through quantitative measurements of several parameters, e.g. graphite fraction, shape, form. Afterward, the same samples were colour etched with picric acid in order to perform a qualitative analysis of the matrix.

It was concluded from the data collected, that molybdenum has a significant influence in the UTS. Such influence, increases the UTS strongly with the amount of molybdenum. It was also found that the pearlitic matrix changes into ausferrite matrix, for the 0.96% of molybdenum, but ausferrite it is detected from 0.65% of molybdenum onwards. Regarding thermal properties, molybdenum does not have noticeable effect but it is possible to see a clear worsen in the conductivity in the specimen, which has ausferrite as matrix.

Graphite does not seem to have a clear behavior with the different concentration of molybdenum but in the other hand, the matrix shows clear differences as it was mention before.

During solid state reaction, it was detected a clear influence of molybdenum additions, where the latent heat and the volumetric change were measured during the eutectoid reaction and show a decreasing behavior for molybdenum contents above 0.65%.

The use of recommended S-N curves, presented in current literature, to analyse and determine the fatigue life of a part is common practice in, inter alia, the construction industry.However, the recommended S-N curves are generally created for larger components used in mainly the construction industry. Hence, the use of S-N curves for the evaluation of smaller parts, may result in over-dimensioning of such parts. For this reason, evaluation and designing of smaller parts could benefit from the development of an in house S-N curve specific for the part.

The purpose of this thesis is to generate and validate an in-house method for creating a S-N curve, for a specific part to be compared with recommended S-N curves in the literature. The specific part used for the generating of the method is a welded steel joint with the geometry of two steel pipes, welded together in a t-formation and which has been provided by Thule AB for the purpose of the thesis.

The method presented uses the results from 1) physical fatigue tests using a fatigue testing machine and 2) static FEA to derive a S-N curve for the specific part using the least squares method. A fatigue testing rig enables the gathering of data of the number of cycles to failure when the part is subject to a given cyclic load. The rig uses pneumatics to control the forces applied onto the part with the use of a cylinder. Furthermore, the fatigue testing rig was designed to be controlled by the applied force, meaning, that the rig ensured a homogeneous load cycle by measuring the force from a load cell and alternating the direction of the cylinder with an electrically controlled pressure valve. The performance of static FEA evaluations aim at locating stresses in the part. For this thesis the stresses were evaluated using the hot spot method due to the part's welded geometry.

The data gathered from the physical fatigue tests and the static FEA evaluations are subsequently combined deriving S-N curves applicable to the part.

From the fatigue tests and FEA evaluations for the t-shaped welded steel part, four S-N curves were derived of which two curves showed the results of a linear fitted curve whereas the other curves used the recommended slope of $-1/3$. The results showed that the S-N curves derived, using a set slope, resulted in similar curves to the recommended S-N curve provided by the literature. However, the linear fitted S-N curve showed that the part, according to the S-N curve, had a higher fatigue resistance than recommended.

 Due to limitations in the thesis work, the S-N curves derived within the framework of this thesis should be regarded as theoretical and have been strictly used to identify whether the method generated is applicable for deriving of S-N curves.

Large caliber gun barrels are exposed to deferent kinds of high strain, from pressure to wear, with influence of chemical, and thermal effects. With the ever increasing demand on better guns, the demand on the barrel increases as well. This study will go through the thermal part of the strain that affect the gun barrel steel. The will be experiment on how thermal cyclic load affect low alloy steel, documentation the cracks, hardness and create computer simulations on the physical experiments.

The heating experiment is carried though by the help of an induction coil that is the supplement for the burring propellant to not get any unwanted chemical residue. The heat and timeframe of one cycle, does not one hundred percent representative the reality but it will still give a got comparison of the materials tested. The experiment was completed on five different material 1.2709-A1, -A2, -B, CrMoV, and H13, which are all used in the tooling industry and therefore interesting material in a gun barrel.

The material show vastly different cracks intensity and crack length, with is connected to grain size, thermal conductivity, coefficient of the thermal expansion, strength, toughness, and hardness. The hardness measurement showed a phenomena that does not happen in a fired gun barrel, which is thermal softening. Thermal softening happens in this test for the simple reason that the temperate was never high enough to make the steel phase change to austenite. This makes the secondary carbide crystals to recrystallize into larger ones to lower their energy, in turn reducing hardness and strength. The simulations show that there is tensile stress at the outside, closest to the induction coil, and compressive stress on the inside of the test sample. It also gave a good insight on how the properties affect the steel. 

The material 1.2709B got the best results from the experiment conducted in the study, few and short cracks, almost nonexistent hardness softening. It has the ductility and toughness to reduce the softening and the strength and thermal conductivity to stand against the major crack formations.

Recent X-ray diffraction (XRD) measurements have revealed that plastic deformation and a residual elastic strain field can be present around the graphite particles in ductile cast iron after manufacturing, probably due to some local mismatch in thermal contraction. However, as only one component of the elastic strain tensor could be obtained from the XRD data, the shape and magnitude of the associated residual stress field have remained unknown. To compensate for this and to provide theoretical insight into this unexplored topic, a combined experimental-numerical approach is presented in this paper. First, a material equivalent to the ductile cast iron matrix is manufactured and subjected to dilatometric and high-temperature tensile tests. Subsequently, a two-scale hierarchical top-down model is devised, calibrated on the basis of the collected data and used to simulate the interaction between the graphite particles and the matrix during manufacturing of the industrial part considered in the XRD study. The model indicates that, besides the viscoplastic deformation of the matrix, the effect of the inelastic deformation of the graphite has to be considered to explain the magnitude of the XRD strain. Moreover, the model shows that the large elastic strain perturbations recorded with XRD close to the graphite–matrix interface are not artifacts due to e.g. sharp gradients in chemical composition, but correspond to residual stress concentrations induced by the conical sectors forming the internal structure of the graphite particles. In contrast to common belief, these results thus suggest that ductile cast iron parts cannot be considered, in general, as stress-free at the microstructural scale. 

In a quest to develop new light metal alloys that can perform excellently at elevated-temperatures (from 300°C to 400°C), a ternary eutectic Al-Cu-Si alloy was exploited to gain a deeper understanding of the alloy system and its suitability for high temperature applications. The alloys studied, with chemical composition of Al-27%Cu-5%Si (by weight percent) with Ni addition in the range of 0 to 1.5%wt, were cast in a rapid solidification casting technique. The solidification characteristics of the alloy was studied using the Thermo-Calc software. Microstructures were characterized in a scanning electron microscope coupled with energy dispersive spectrometry (SEM-EDS). Finally, the elevated-temperatures tensile properties of the alloys were investigated. Comparing the microstructures and mechanical properties of these Al-Cu-Si(-Ni) alloys with conventional Al-Si alloy A319, the refined microstructure with dispersed Ni intermetallic particles formed in the as-cast Al-Cu-Si(-Ni) alloys deliver improved elevated temperature properties. In particular, the yield strength and ultimate tensile strength of the new alloy with 1.5% Ni at 400?C were observed to be 220% and 309% higher, respectively, than for conventional A319 alloy.

Abstract

The aim of this thesis is to investigate the influence of Strontium (Sr) addition on the microstructure formation, including porosity and the mechanical properties of commercial Aluminum alloy ENAC 46000. In addition, it is intended to obtain an optimum Sr level in order to achieve the desired mechanical properties.

Specimens were prepared with gradient solidification technique at different cooling rates in order to achieve samples with a variety of microstructural coarseness. Beside microstructural and mechanical properties studies, thermal analysis was employed to keep track of the time and temperature of phases during solidification.

The achieved results indicate that Sr affects the mechanical properties except the strength. The analysis of the result indicates that the optimum level of Sr is 150 ppm.

Porosity is a function of both Sr addition and cooling rate. Comparing the influence of cooling rate with Sr addition on the amount of porosity shows that the cooling rate can modify the ENAC 46000 alloy more than Sr addition.

Thermal analysis technique used to study effect of phase formation on modification. Influence of solidification rate and Sr level on time and temperature of α-Al (Τ_α) and Al-Si eutectic (Τ_N) nucleation was observed.

Inom forskningsområdet Ytteknik används modellering och simulering bland annat för att analysera ytbeläggningsprocesser på komplexa geometrier. Detta är ett multidisciplinärt område som täcker bl.a. elektrokemi, jontransport och Computational Fluid Dynamics (CFD) för beräkningar av strömningsfenomen. Numeriska modelleringsverktyg används i utformandet av processen för att optimera processparametrar både med avseende på ytbeläggningens struktur och förbättrad fördelning av ytbeläggningen. Genom M-ERA projektet som finansierats av VINNOVA har en modell tagits fram för att beskriva ytbeläggning av silver av ett gjutet radiofilter i en silvercyanidlösning. Med målet att ha en minsta ytbeläggningstjocklek på 1 μm har både den elektriska strömmen och ytbeläggningstiden varierats för att uppnå en jämn ytbeläggning och minska förbrukningen av silver. Med hjälp av mätningar på komponenter har man även kunnat validera modellerna.

Understanding and evaluating the performance of different powder and substrate materials combined in the laser cladding/alloying layer is prioritised by process and material engineers to obtain high-quality durable surfaces. The surface quality is usually determined by the combination of various process parameters, such as laser power, powder feeding rate, and scanning speed, that result in different dilution ratios. Furthermore, process parameter calibration highly depends on the surface geometry and alignment of the deposited tracks. The application of simulation tools for the manufacturing process design tends to reduce experimental efforts. However, laser surface cladding and alloying represents a complex manufacturing process, where powder deposited on the surface of a material solidifies and forms an alloy with the substrate. Full-scale process simulation is often not feasible for parametric studies aiming at tuning the process parameters.  

The present work introduces an experimentally validated simulation methodology, including a simplified three-dimensional finite-element heat transfer model of the laser surface cladding/alloying process, Figure 1. Cladding/alloying of a nickel-based superalloy powder on the grey cast iron substrate has been studied. With the help of laser cladding experiments and measurements on cross-section images, it has been shown that the model is capable to predict the actual laser power to obtain the desired penetration depth into the substrate, heat-affected zone size and dilution ratio. It is shown by introducing a laser power scaling factor that the model input and comparison data can be obtained from a single cladding/alloying experiment. 

Thermal conductivity is an important property for many iron cast components, and the lack of widely accepted thermal conductivity model for cast iron, especially grey cast iron, motivates the efforts in this research area. The present study contributes to understanding the effects alloy microstructure has on thermal conductivity. A thermal conductivity model for a pearlitic cast iron has been proposed, based on the as-cast alloy composition and microstructural parameters obtained at different solidification rates. According to the model, available parallel heat transfer paths formed by connected graphite flakes across eutectic cells are determined by the space between dendrite arms. The uncertainties both for model inputs and for validation measurements have been estimated. Sensitivity analysis has been conducted to result in better understanding of the model behaviour. The agreement between modelled and measured thermal conductivities has been achieved within 5% on the average for the investigated samples.

Thermal conductivity is an important property for cast components produced from different types of cast iron. Development of a general widely-accepted thermal conductivity model for compacted and lamellar graphite irons poses a research challenge. The present study extends the modeling approach introduced earlier for pearlitic lamellar graphite iron toward compacted graphite iron and ferritic lamellar graphite iron. The proposed thermal conductivity model of the bulk material is based on the alloy microstructure and Si segregation between eutectic cells and non-cell regions, at the main assumption that the heat paths in the eutectic cells are formed by connected graphite phases surrounded by ferrite phases. The overall thermal resistance of these heat paths is determined by the hydraulic diameter of the interdendritic region. The uncertainties both for the modeled and for experimentally derived thermal conductivities have been estimated. The importance of considering the Si segregation in the model has been discussed. For the investigated samples, the agreement between modeled and measured thermal conductivities has been achieved within 4% on the average, at the same value of the single fitting parameter found for pearlitic, pearlitic–ferritic lamellar, and compacted graphite iron alloys. The results contribute to the understanding of the material microstructure effects on the cast iron thermal conductivity.

In striving to produce high quality cast components from recycled aluminium alloys,imperfections have to be considered, because recycled aluminium usually containsmore of it. However, there are great energy savings to be made by using recycledaluminium; as little as 5% of the energy needed for primary aluminium productionmay be required. High quality castings are dependent on, besides alloy chemistry, bothmelt quality and the casting process; the focus of this work is related to the meltquality.This thesis aims to increase knowledge about imperfections, foremost about Fe-richparticles, oxides/bifilms, and porosity. Experiments were performed at industrialfoundry facilities and in a laboratory environment. Melt quality was evaluated byproducing samples with the reduced pressure test (RPT), from which both densityindex (DI) and bifilm index (BI) could be measured, results that were related to tensiletest properties. Data from tensile test samples were analysed, and fracture surfacesand cross sections were studied in both light microscope and in scanning electronmicroscope (SEM). For the purpose of investigating nucleation of primary Fe-richparticles (sludge) differential scanning calorimetry (DSC) was used.In the analysis of results, a correlation between the morphology of particles and tensileproperties were found. And elongated Fe-rich β-particles were seen to fracturethrough cleavage towards the centre. However, DI and BI have not been possible torelate to tensile properties.The nucleation temperature of primary Fe-rich particles were found to increase withincreased Fe, Mn, and Cr contents, i.e. the sludge factor (SF), regardless of cooling rate.For a set SF, an increase of cooling rate will decrease the nucleation temperature.

There are great energy savings to be made by recycling aluminium; as little as 5% of the energy needed for primary aluminium production may be required. Striving to produce high quality aluminium castings requires knowledge of microstructural imperfections, which is extra important when casting recycled aluminium that generally contains higher levels of imperfections compared to primary aluminium. Imperfections include amongst others Si, Fe, and Mn as well as oxides. Si is needed for castability, but it may also initiate fracture. There are different types of Fe-rich intermetallics influencing properties of castings, generally in a negative direction. Oxides constitute cracks and they are elusive because they are difficult to quantify.

This thesis aims to increase knowledge about imperfections in recycled aluminium castings originating from alloying elements and the melt. Experiments were performed in advanced laboratory equipment, including X-radiographic imaging during solidification and in-situ tensile testing in a scanning electron microscope. Experiments were also performed at industrial foundry facilities.

The experiments showed that the nucleation temperature of primary α-Fe intermetallics increased with higher Fe, Mn, and Cr contents. Primary α-Fe are strongly suggested to nucleate on oxides and to grow in four basic morphologies. Lower nucleation frequency of α-Fe promoted faster growth and hopper crystals while higher nucleation frequency promoted slower growth rates and massive crystals. Results also showed that a decrease in the size of the eutectic Si and plate-like β-Fe intermetallics improved tensile properties, foremost the elongation to fracture. In β-Fe containing alloys the transversely oriented intermetallics initiated macrocracks that are potential fracture initiation sites. In alloys with primary α-Fe foremost clusters of intermetallics promoted macrocracks. In fatigue testing, a transition from β-Fe to α-Fe shifted the initiation sites from oxides and pores to the α-Fe, resulting in a decrease of fatigue strength. Oxides in Al-Si alloys continue to be elusive; no correlations between efforts to quantify the oxides and tensile properties could be observed.

Morphology and growth of primary α-Al(FeMnCr)Si intermetallics have been studied in-situ during solidification of a commercial secondary aluminum alloy employing X-radiographic imaging combined with deep-etching. The α-Al(FeMnCr)Si intermetallics were found to nucleate primarily on surface oxides, and the continued growth yielded both rhombic dodecahedrons and elongated rod-like morphologies. Both morphologies were observed as hopper and massive types, where the hopper intermetallics had the higher growth rates. The growth rate, which determines the type, appears to be linked to nucleation frequency; higher nucleation frequency promoted massive types and lower nucleation frequency promoted hopper intermetallics. 

To evaluate the role of Fe-rich intermetallics on crack initiation, two fully modified Al-Si alloys, one containing plate-like β-Fe and the second containing primary α-Fe intermetallics, were investigated by in-situ tensile testing in the scanning electron microscope. In the first alloy, large plate-like β-Fe intermetallics oriented parallel to the test direction were the first to crack at an elongation of about 1.8%. More transversely oriented intermetallics caused crack initiation in the matrix which linked up with the final fracture. In the second alloy, the cracking of α-Fe intermetallics initiated at an elongation of about 0.9%. It is concluded that large α-Fe intermetallics crack first and that clusters of α-Fe are the most potent crack initiation sites.

The relationship between microstructure and mechanical properties in cast aluminium alloys is very complex. This relationship is also strongly affected by the casting process and melt handling. In the current study the mechanical properties were investigated and correlated with microstructural features such as porosity, Fe-rich particles, SDAS, Si-length. Process quality measures such as bifilm index, density index, and sludge factor were also investigated. The aim of the work was to understand the critical interactions between material microstructure and process quality in the development of high performance materials.

The effect of Fe-rich particles has been a topic for discussion in the aluminum casting industry because of the negative impact they exert on the mechanical properties. However, there are still contradictions on the effects of various morphologies of Fe-particles. In this study, microstructural characterization of tensile tested samples has been performed to reveal how unmodified and modified Fe-rich particles impact on the tensile behavior. Analysis of additions of Fe modifiers such as Mn and Cr, showed higher amounts of primary Fe-rich particles (sludge) with increased porosity and, as result, degraded tensile properties. From the fracture analysis of tensile tested HIPed samples it could be concluded that the mechanical properties were mainly governed by the Fe-rich particles, which were fracturing through cleavage, not by the porosity.

Recycled aluminium alloys manufactured at Stena Aluminium, in Älmhult, Sweden, are delivered in special designed transport containers, called thermoses. Thermoses are best described as an insulating layer protected by a steel cover with a heat loss of about 5 degrees/h. Three thermoses are transported by a truck, giving the possibility for a total capacity of about 24 tonnes delivered aluminium just-in-time to the foundry. By delivering a full load of liquid aluminium, about 2 tonnes of carbon dioxide emissions are saved, compared with delivering ingots. The aim of the paper is to assess the quality benefits, in terms of inclusions sedimentation and mechanical properties, assured by delivering aluminiummelts instead of ingots. The results indicate that materials produced by just-in-time melt delivery have slightly improved quality compared to ingots. The trends are explained in terms of quality, density and bifilm indexes, based on microstructural observations as well as tensile test data analysis.

Aluminium-silicon alloys have gained increasing market share in the automotive and aerospace industry because of increased environmental demands. These alloys have a high strength-to-weight ratio, good corrosion resistance, castability and recycling potential. However, variations in properties and limited performance at elevated temperature are restricting these alloys from use at elevated temperatures. During the last decades, researchers have investigated ways to improve the properties at elevated temperatures. However, the effect of some transition elements is not well understood. The aim of this work is to investigate the aluminium-silicon alloys with addition of cobalt and nickel for high temperature applications. Tensile testing and hardness testing were conducted on samples produced by directional solidification in a Bridgman furnace with condition generating a microstructure corresponding to that obtained in high pressure die casting, i.e. SDAS ~ 10 µm. The results show that cobalt and nickel improve the tensile properties up to 230 °C.

Global warming is driving industry to manufacture lighter components to reduce carbon dioxide (CO₂) emissions. Promising candidates for achieving this are aluminium-silicon (Al-Si) cast alloys, which offer a high weight-to-strength ratio, excellent corrosion resistance, and good castability. However, understanding variations in the mechanical properties of these alloys is crucial to producing high-performance parts for critical applications. Defects and oxides are the primary reasons cast components in fatigue applications are rejected, as they negatively impact mechanical properties.

A comprehensive understanding of the correlation between fatigue performance and parameters such as the α-aluminium matrix, Al-Si eutectic, surface roughness, porosities, hydrogen content, oxides, and intermetallic phases in Al-Si castings has not been reached.

The research presented in this thesis used state-of-the-art experimental techniques to investigate the mechanical properties and crack-initiation and propagation behaviour of Al-Si-Mg cast alloy under cyclic loading. In-situ cyclic testing was conducted using scanning electron microscopy (SEM) combined with electron back-scattered diffraction (EBSD), digital image correlation (DIC), and focused ion beam (FIB) milling. These techniques enabled a comprehensive study of parameters affecting fatigue performance, including hydrogen content, surface roughness, oxides, and intermetallic phases. More specifically, we investigated the effect of melt quality, copper (Cu) content, oxide bifilms, surface quality, and porosity.

The increased Cu concentration in heat-treated Al-Si alloys increased the amount of intermetallic phases, which affected the cracking behaviour. Furthermore, oxide bifilms were detected at crack-initiation sites, even in regions far away from the highly strained areas. Si- and Iron (Fe)-rich intermetallics were observed to have precipitated on these bifilms. Due to their very small size, these oxides are generally not detected by non-destructive inspections, but affect mechanical properties because they appear to open at relatively low tensile stresses. Finally, Al-Si alloy casting skins showed an interesting effect in terms of improving fatigue performance, highlighting the negative effect of surface polishing for such alloys.

For reducing the CO2 footprint in many industrial fields, the goal is to produce lighter components. The aluminium-silicon (Al-Si) cast alloys are promising candidates to fulfill these goals with a high weight-to-strength ratio, good corrosion properties, excellent castability, and recyclable material. However, the variations within these components need to be understood to produce high-performance components for critical applications. The main reason for the rejection in these applications is defects and microstructural features that reduce the mechanical properties. The addition of copper (Cu) is one way of increasing the mechanical properties in Al-Si alloys and is commonly used in the automotive industry. Casting defects harm the mechanical properties, and these defects can be reduced by improving the melt quality, the correct design of the component, and the gating system.

The study aims to investigate the static mechanical properties and the crack initiation and propagation under cyclic loading in an Al-7Si-Mg cast alloy with state-of-the-art experiments. The main focuses were on the effect of the HIP process and the role of Cu addition. In-situ cyclic testing using a scanning electron microscope coupled with electron back-scattered diffraction, digital image correlation, focused ion beam (FIB) slicing, and computed tomography scanning was used to evaluate the complex interaction between the crack path and the microstructural features.

The amount of Cu retained in the α-Al matrix in as-cast and heat-treated conditions significantly influenced the static mechanical properties by increasing yield strength and ultimate tensile strength with a decrease in elongation. The three-nearest-neighbor distance of eutectic Si and Cu-rich particles and crack tortuosity were new tools to describe the crack propagation in the alloys, showing that a reduced distance between the Cu-rich phases is detrimental for the mechanical properties. Three dimensional tomography using a FIB revealed that the alloy with 3.2 wt.% Cu had a significantly increased quantity of cracked Si particles and intermetallic phases ahead of the crack tip than the Cu-free alloy. The effect of Cu and HIP process in this work shows the complex interaction between the microstructural features and the mechanical properties, and this needs to be considered to produce high-performance components.

Increasing environmental demands are forcing the automotive industry to reduce vehicle emissions by producing more light-weight and fuel efficient vehicles. Al–Si alloys are commonly used in automotive applications because of excellent castability, high thermal conductivity, good wear properties and high strength-to-weight ratio. However, most of the aluminium alloys on the market exhibit significantly reduced strength at temperatures above 200 °C. This paper presents results of a study of the effects of Co and Ni in a hypoeutectic Al–Si alloy on microstructure and mechanical properties at room and elevated temperature. Tensile test specimens with microstructures comparable to those obtained in high-pressure die casting, i.e. SDAS ~ 10 µm, were produced by directional solidification in a Bridgman furnace. The results show an improvement in tensile properties up to 230 °C.

In the last decades, the automotive industry has increased the usage of cast aluminum. To enhance the quality of their products, foundries must focus on minimizing casting entrainment defects during the production process. Defects can be divided into visible and hidden damage to the structural component. The visible defects, such as pores and bubbles, have been the primary focus of quality assurance in foundries. Yet, recent evidence shows that most of the damage given to liquid metals remain hidden, only to reduce tensile properties and fatigue performance in service.This work presents ways to identify the hidden damage in cast aluminium using in-situ cyclic testing in a scanning electron microscope equipped with a Focused Ion Beam. Moreover, applying Digital Image Correlation to cyclic tests and tensile tests showed the hidden damage in an early stage.The combined results show that the hidden damage impacts the mechanical properties significantly.

Al-Si alloys are the most popular casting alloys due to their excellent castability combined with high strengthto-weight ratio. This paper investigates the role of Si content in the range of 6.5 wt. % to 14.4 wt. % on the microstructure and mechanical properties of Al-Si-Mg casting alloys. All alloys were modified with 90-150 ppm Sr. No grain refiner was added. The samples were produced by directional solidification providing a microstructure that corresponds to microstructures found in die castings. From the phase diagram and coupled zone, increasing the Si level up to 14.4 wt. % is expected to start a competition between formation of α- dendrites and a fully eutectic microstructure. However, it is known that Sr-modification shifts the eutectic to higher Si contents. For the lower Si contents, the microstructure of the samples consisted of α-dendrites and a modified Al-Si eutectic. At 12.4 wt. % Si and above, a cellular eutectic microstructure was observed. No primary Si was observed even at 14.4 wt. % Si. The mechanical properties in terms of yield and tensile strength did not vary remarkably as a function of the Si level unlike the elongation to failure that dropped from 12 % at 6.5 wt. % Si to nearly 6 % at 14.4 wt. % Si; but still the material is exhibiting an elongation to failure that is far higher than normally expected.

A new simple approach was developed to assess the Complete Melt Quality of aluminium cast alloys throughout the production line. The approach relies on the concurrent use of reduced pressure tests (RPT) and tensile tests at each station in the production line when the melt is transferred and/or processed. These tests can be used to determine the source of melt-related problems in the production line. Two case studies from the procedure of both an aluminium die-casting and a rheo-casting plant showed that melts were significantly damaged in the tower furnace and got progressively more damaged through the production line proven by the RPT, tensile test, and fracture surface analysis results.

Al–Si–Cu alloys were cast with the unique gradient solidification technique to producealloys with two cooling rates corresponding to secondary dendrite arm spacing (SDAS) of ∼9 and ∼27 μm covering the microstructural fineness of common die cast components.The microstructure was studied with optical microscopy and scanning electronmicroscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and electronbackscattered diffraction (EBSD). The alloy with higher cooling rate, lower SDAS, hasa more homogeneous microstructure with well distributed network of eutectic and intermetallicphases. The results indicate the presence of Al–Fe–Si phases, Al–Cu phases andeutectic Si particles but their type, distribution and amount varies in the two alloys withdifferent SDAS. EBSD analysis was also performed to study the crystallographic orientationrelationships in the microstructure. One of the major highlights of this study is theunderstanding of the eutectic formation mechanism achieved by studying the orientationrelationships of the aluminum in the eutectic to the surrounding primary aluminumdendrites.

The mechanical properties of Al-Si alloys are affected by several microstructural features such as secondary dendrite arm spacing (SDAS), size and shape of eutectic Si-particles, presence of intermetallics as well as by porosity. In the current study, Al-Si-Cu alloy A380 was prepared by a unique directional solidification method to produce samples with two different SDAS of 9 μm and 27 μm. The lower solidification rate resulted in larger SDAS, larger grain size, larger eutectic Si and larger intermetallics including Fe-rich β phase. The microstructure with higher solidification rate was found to be finer and more homogeneous with smaller eutectic Si and intermetallics. The specimen with larger SDAS exhibited stronger texture than the one with smaller SDAS. The specimen with smaller SDAS showed improved mechanical properties including YS, UTS and ductility. 

In this work the influence of the ingate system design on the as-cast mechanical properties of an Al-10Si-0.38Mg alloy have been clarified. The Weibull distribution has been seen to describe the spread in mechanical properties very well. The Weibull modulus has therefore been used as a measure of the soundness of an ingate system. Different ingate systems were investigated, including: expanding systems, pressurised systems, systems with and without filter, systems with different designs of the connection between the downsprue and the runner, and systems with and without an additional pocket at the end of the runner. The modification index of the microstructure was also measured in order to investigate if the spread in data is more dependent on the modification index than on the ingate system design. The results showed that a high Weibull modulus is more dependent on the ingate system design than on the modification index of the microstructure. The ultimate tensile strength was not significantly affected by the ingate system design, while the fracture elongation seemed to be more dependent on the melt quality than on the ingate system design. The Weibull modulus indicates that expanding systems are better than pressurised systems, and that the use of a filter in the runner is very beneficial. An additional pocket at the end of the runner has no beneficial effect when using a filter. The connection between the downsprue and the runner should have a rounded bend and the change in cross-section between the downsprue and the runner should be chamfered and not sharp.

Aggregate molding, or sand casting, is the gravity pouring of liquid metal into a mold that is made of a mixture molded against a permanent pattern. This article summarizes the most important materials in the process of sand casting of cast iron, including different types of molding aggregates, clays, water, and additives in green sand, chemically bonded organic resins, and inorganic binders in self-setting, thermosetting, and gas-triggered systems. It discusses three main types of reclamation systems: wet, dry, and thermal. The article concludes with a description of both nonpermanent and permanent mold processes.

During air-slip direct chill casting of aluminum billets, one of the major defects occurring includes traces along the billet called vertical drags (VDs). If the VDs are too deep or too many, then they cause scraping of the billets. As in the subsequent extrusion process, the surface quality is known to impair both the productivity and quality of the profiles. In cast-house practice, many theories circulate about the causes of VD defects and how to avoid them, but in the literature, no thorough treatments have been made to explain this phenomenon. In the current study, the outer appearance, structure around, and compositions at the defects are analyzed. A theory for the formation of the defects, their cause, and how their appearance is coupled to different alloy types is presented. The segregation in the vicinity of the defects is discussed based on deformation of semisolid materials and coupled to Reynolds dilatancy ingranular materials. The theory can explain differences between 6063 and 6005 alloys.

Al-Si-Mg alloys are widely used in the automotive industry for the production of engine components. Due to the new stringent emissions standards, these components undergo highertemperatures than in the past; as a result, alloys with higher thermal stability, such as the Al-Si-Cu-Mg, are currently under investigation.The present paper aims at widening the knowledge on the relationship between room temperature (RT) and high temperature fatigue behaviour of A354 and C355 alloys and their microstructural features, in particular, secondary dendrite arm spacing (SDAS) and intermetallic compounds. Samples for fatigue characterization were hot isostatic pressed, aiming to avoid the effect of solidification defects.The results of microstructural analyses and rotating bending fatigue tests highlighted that (i) SDAS influences room temperature fatigue behaviour of the peak-aged A354 and C355 alloys, while its effect on the overaged alloys at high temperature is negligible; (ii) fatigue cracks nucleated mostly from large intermetallic compounds; (iii) at room temperature, C355 alloy is characterized by higher fatigue strength (151 and 135. MPa for fine and coarse SDAS, respectively) in comparison to A354 alloy (133 and 113. MPa); after overaging and testing at high temperature, the behaviour of the two alloys is comparable. A good correlation between ultimate tensile strength and fatigue resistance was found, independent of microstructure and aging condition.

The book looks into the recent advances in the ex-situ production routes and properties of aluminum and magnesium based metal matrix nanocomposites (MMNCs), produced either by liquid or semi-solid state methods. It comprehensively summarizes work done in the last 10 years including the mechanical properties of different matrix/nanoreinforcement systems. The book also addresses future research direction, steps taken and missing developments to achieve the full industrial exploitation of such composites. The content of the book appeals to researchers and industrial practitioners in the area of materials development for metal matrix nanocomposites and its applications.

The high temperature tensile behaviour of the A354 casting aluminum alloy was investigated also evaluating the influence of secondary dendrite arm spacing (SDAS). Cast specimens were produced through a gradient solidification equipment, obtaining two different classes of SDAS, namely 20-25 µm (fine microstructure) and 40-50 µm (coarse microstructure). After hot isostatic pressing and T6 heat treatment, the samples underwent mechanical characterization both at room and high temperature (200 °C). Results of tensile tests and hardness measurements were related to the microstructural features and fractographic characterization, in order to investigate the effect of microstructure and high temperature exposure on the mechanical behaviour of the alloy.

The aims of the present work are to evaluate the overaging behaviour of the investigated Cu-enriched alloy and to assess its mechanical behaviour, in terms of the tensile and fatigue strength, at room temperature and at 200 °C, and to correlate the mechanical performance with its microstructure, in particular with the secondary dendrite arm spacing (SDAS). The mechanical tests carried out on the overaged alloy at 200 °C indicate that the addition of about 1.3 wt.% Cu to the A357 alloy enables to maintain ultimate tensile strength and yield strength values close to 210 and 200 MPa, respectively, and fatigue strength at about 100 MPa. Compared to the quaternary (Al−Si−Cu−Mg) alloy C355, the A357−Cu alloy has greater mechanical properties at room temperature and comparable mechanical behaviour in the overaged condition at 200 °C. The microstructural analyses highlight that SDAS affects the mechanical behaviour of the peak-aged A357−Cu alloy at room temperature, while its influence is negligible on the tensile and fatigue properties of the overaged alloy at 200 °C. 

Al-Si-Cu alloys are the most widely used materials for high-pressure die casting processes. In such alloys, Fe content is generally high to avoid die soldering issues, but it is considered an impurity since it generates acicular intermetallics (β-Fe) which are detrimental to the mechanical behavior of the alloys. Mn and Cr may act as modifiers, leading to the formation of other Fe-bearing particles which are characterized by less harmful morphologies, and which tend to settle on the bottom of furnaces and crucibles (usually referred to as sludge). This work is aimed at evaluating the influence of sludge intermetallics on the fatigue behavior of A380 Al-Si-Cu alloy. Four alloys were produced by adding different Fe, Mn and Cr contents to A380 alloy; samples were remelted by directional solidification equipment to obtain a fixed secondary dendrite arm spacing (SDAS) value (~10 µm), then subjected to hot isostatic pressing (HIP). Rotating bending fatigue tests showed that, at room temperature, sludge particles play a detrimental role on fatigue behavior of T6 alloys, diminishing fatigue strength. At elevated temperatures (200◦C) and after overaging, the influence of sludge is less relevant, probably due to a softening of the α-Al matrix and a reduction of stress concentration related to Fe-bearing intermetallics.

Al-Si-Cu alloys with high Fe content are widely employed in high pressure die casting (HPDC). Even if Feis usually considered an impurity in secondary aluminum alloys, leading to the formation of harmfulintermetallic compounds, it helps in mitigating or eliminating the problem of die soldering. As a result,secondary Al alloys with Fe content of about 1 wt% are commonly employed for the production of HPDCcastings. Aiming to change the morphology of harmful Fe-bearing phases towards less detrimentalmorphologies, proper alloying elements may be added to the alloys. Mn and Cr (both present in thealuminum scrap), as instance, are reported to prevent from the formation of the acicular β-Al5FeSi phase,leading to the formation of more compact and polygonal intermetallics. Such phases are usually referredto as “sludge” particles. The influence of sludge particles on mechanical properties of Al -Si-Cu castings isstill under investigation. The present work aims at evaluating the effect of impurities (Fe, Mn and Cr)typically present in secondary Al alloys on the microstructure and mechanical properties of the A380 (Al -Si-Cu) alloy. Samples with different Fe, Mn and Cr content were produced and processed through adirectional solidification equipment to obtain specimens with controlled SDAS (~10 μm). Hardness androtating bending fatigue tests were carried out at room temperature. Mechanical properties of the alloyswere then related to the microstructure, analyzed by optical and scanning electron microscopy.

Al-Si-Mg alloys are commonly employed for the production of automotive castings. In view of the recent stringent emissions standards and consequent engine downsizing, these components must withstand higher temperatures and stresses than in the past. In this regard, the heat treatable quaternary Al-Si-Cu-Mg alloys gained particular interest in recent years, due to their superior mechanical properties and higher thermal stability. The present research activity was addressed to evaluate the influence of cooling rate on microstructure and consequently on room temperature tensile and fatigue behaviour of the A354 and C355 alloys. Samples for mechanical tests were produced under controlled cooling rates, in order to induce different secondary dendrite arm spacing (SDAS) values, classified as fine (20-25μm) and coarse (50-70μm). The experimental results showed that the cooling rate strongly influences the type, size and morphology of intermetallic particles. The presence of coarse intermetallic phases, mostly Fe-based, observed in coarse SDAS specimens, was reported to strongly affect ultimate tensile strength (UTS), elongation to failure and fatigue strength of both the investigated alloys. A correlation between UTS and fatigue resistance was found, independent of microstructural coarseness.