Three significant changes are driving the use of materials in the automotive industry today. First, the direct environmental load of materials drives the issue of climate change through the associated carbon footprint of the car from manufacturing to use and end-of-life phases. The new consumer attitudes and legislation force new requirements on the automotive industry. These requirements constitute the second driver, pushing the electrification of the drive line and the use of batteries. The electrification significantly simplifies the car's architecture and allows for a more significant functional integration of the automotive components. This leads to functional integration in component design, considerably changing the conditions to the third driver, consisting of reduced raw material use, material efficiency and recycling and how to achieve cost-effectiveness and resource efficiency. Closing the circle to the climate impact and the carbon footprint changes dramatically. The current paper reviews and analyses the consequences of electrification and the use of Giga casting on aluminium alloys, especially alloying element streams, for recycling in the automotive industry, targeting a near-closed-loop approach. This analysis is made to identify potential resource quality and availability issues for the aluminium alloys and the alloying elements used. It was concluded that there would be a significant need for primary or non-automotive aluminium scrap to be introduced into the flow. All electrified drivelines will allow for a closed-loop scenario where Mg, Si and Mn are the first to reach surplus and Fe, Zn, and Cu are the last. Critical is that the additions of Si made in the recycling process can, in theory, be eliminated. Si is responsible for more than half the carbon footprint of aluminium alloy recycling.

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.

A hot isostatically pressed specimen of the A357 alloy in T6 condition has been tested for fatigue performance in situ. During testing, multiple small cracks were observed during the first cycle, both in proximity to and far from the stress concentration. These cracks have competed to form a propagating crack, forming multiple crack paths initially. Once the propagating crack has been established, it has chosen paths from multiple cracks that have opened around the tip to grow further. All small cracks observed to open have been attributed to bifilms, i.e., liquid metal damage. It is imperative to develop processes that minimize liquid metal damage to enhance the fatigue performance of aluminum alloy castings.

Tensile tests have been conducted on die-cast coupons of an Al-Si-Cu alloy, which have been found to contain no pores via X-ray inspection. Due to the digital image correlation used during tensile testing, either single or multiple strain concentrations have been detected and subsequently characterized. In all cases, oxide films have been found on fracture surfaces at the site of the strain concentrations. The analysis of a crack away from the fracture surface has also shown it to be an oxide bifilm. These results pour doubt on the effectiveness of quality assurance practices employed in industry.

The competition between pores and hidden entrainment defects during tensile testing of specimens from Al-Si-Cu alloy high-pressure die castings has been characterized. In all tests, multiple strain concentrations have been identified by using the digital image correlation technique and the final fracture has been preceded by a competition between pores and hidden damage, later identified as oxide bifilms. The results have confirmed previous findings that overall damage to the metal during its liquid state is much more extensive than what can be assessed via X-ray inspection, which looks only for pores. It is concluded that current quality assurance techniques need to be updated.

An approach to evaluate and quantify process variability in the mechanical performance of castings is explored. The process variability describes the effect of hidden damage given to the metal before solidification on the material performance measured by elongation to failure. The approach is demonstrated on a casting produced by high-pressure die casting (HPDC) with different filling conditions in serial production. Statistical analyses have been conducted on data obtained from several positions throughout the casting to determine whether a position is performing differently from other positions. The results show that elongation in most positions follows the same Weibull distribution. However, the local evaluation shows that one position stands out and follows a separate distribution. Casting simulations, Digital Image Correlation (DIC), and Scanning Electron Microscopy (SEM) reveal that this position displays an increased amount of hidden damage that causes the local reduction in elongation. The investigated changes in prefill amount do not significantly affect the material quality, which is more controlled by the quality of the melt and the nature of mold filling.

This study investigates the effect of hot isostatic pressing (HIPping) on the static and fatigue properties of sand-casting A356 aluminium alloys. HIPping is a method to improve the fatigue properties in aluminium cast material by reducing or eliminating the inner porosities. Investigation of the complex interaction between the microstructural features on mechanical properties before and after the HIPping process was examined using computed tomography and scanning electron microscopy (SEM). Castings generally contain pores and defects that have a detrimental impact on the fatigue properties. The HIPping process closes the porosities in all investigated samples with an increase in density. Without significant defects, the mechanical performance improved in the finer microstructure. However, a considerable variation in the results was found between the different conditions, whereas the coarser microstructure with larger porosities before HIPping showed remarkably reduced results. The high-cycle fatigue-tested samples showed reduced fatigue propagation zone in the coarser microstructure. Moreover, large cleavage areas containing bifilms in the fracture surfaces indicate that the healing process of porosities is inefficient. These porosities are closed but not healed, resulting in a detrimental effect on the static and dynamic properties.

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.