The RheoMetal process (previously called the Rapid S- and RSF- process) is a novelmethod to produce cost effective, high quality, semisolid slurries for component casting. TheRheoMetal process uses an Enthalpy Exchange Material (EEM) as cooling agent to absorb heat andproduce a slurry. Critical process parameters to create a slurry by robust melting of the EEM arealloy content, stirring speed, EEM to melt ratio, EEM temperature, EEM microstructuralcharacteristics and melt superheat.In this paper, the melting sequence and melting rate of the EEM was studied experimentally. Theeffect of EEM composition, as well as superheat, on evolution of shape and dimension of the EEMduring stirring was investigated. Initial material freezing onto the EEM was observed, followed by astationary phase with subsequent gradual melting of the EEM. It was shown that the characteristicsof freeze-on layer were strongly correlated to melt superheat, EEM temperature, as well as materialcomposition, hence also has significant influence on the melting sequence.

In the current paper, a low-Si aluminium alloy (1.4-2.4% Si) was used to fabricate acomplex shape telecom component using Semi-Solid High-Pressure Die Cast (SSM-HPDC),process. Microstructure and fracture characteristics were investigated. The cast material exhibitedmicrostructural inhomogeneity, in particular macrosegregation in the form of liquid surfacesegregation bands in addition to sub-surface pore bands and gross centre porosity. Tensilespecimens were taken from the cast components. Elongation and microstructural inhomogeneitywere investigated and correlated. Fracture surfaces of the tensile specimen were examined underscanning electron microscope (SEM). The study showed that both near surface liquid segregationbands and subsurface porosity strongly affected the fracture behaviour. Dominant for loss ofductility was gross centre porosity. The centre porosity was found to be a combination of trappedgas and insufficient, irregular feeding patterns.

The growing demand for increasingly more cost and energy effective electronics components is a challenge for the manufacturing industry. To achieve higher thermal conductivity in telecom components, an aluminum alloy with a composition of Al-2Si-0.8Cu-0.8Fe-0.3Mn was created for rheocasting. Yield strength and thermal conductivity of the material were investigated in the as cast, T5 and T6 heat-treated conditions. The results showed that in the as-cast condition thermal conductivity of 168 W/mK and yield strength of 67 MPa was achieved at room temperature. A T5 treatment at 200°C and 250°C increased thermal conductivity to 174 W/mK and 182 W/mK, respectively, while only a slight increase in yield strength was observed. Moreover, a T6 treatment resulted in similar thermal conductivity as the T5 treatment at 250°C with no significant improvement in yield strength. Therefore, the T5 treatment at 250°C was suggested as an optimum condition for the current alloy composition.

Four Al-Si-Mg-Fe alloys with Si contents varying from 1.6 to 4.5 wt pct were rheocast, using the RheoMetal™ process to prepare slurry and cast in a vertical high-pressure die casting machine. Particle size and Si concentration in the α-Al particles in the slurry and in the as-rheocast component were investigated. A uniform distribution of Si in the globular α ₁-Al particles was achieved in the slurry. In the rheocast samples, measurement of the α ₁-Al particles showed that these particles did not increase significantly in size during pouring and secondary solidification. The two additional α-Al particles types, α ₂-Al particles and α ₃-Al particles, were identified as being a result of two discrete nucleation events taking place after slurry production. The Si concentration in the α ₂-Al and α ₃-Al particles indicated that the larger α ₂-Al particles precipitated before the α ₃-Al particles. In addition, in the as-rheocast condition, the Si distribution inside the α ₁-Al particles showed three distinct zones; an unaffected zone, a transition zone, and in some cases the start of a dendritic/cellular zone. The phenomenon of dendritic growth of globular α ₁-Al particles during secondary solidification occurred concomitantly with the final eutectic reaction and increased with increasing amount of the Al-Si eutectic phase.

The thermal conductivity of a rheocast telecom component produced using Al-6Si-2Cu-Zn alloy (Stenal Rheo 1) was investigated in the as-cast, T5 and T6 conditions. Conventionally liquid cast samples were produced in a permanent mold and used as a reference material. In the rheocast component in as-cast condition, a thermal conductivity of 153 W/mK at room temperature were measured. A T5 treatment at 250 or 300°C increased thermal conductivity to 174 W/mK. A T6 treatment resulted in further increase in thermal conductivity to 182 W/mK. The liquid cast alloy exhibited a lower thermal conductivity and a higher hardness for all conditions compared to the as-rheocast component.The microstructure of rheocast component showed material consisted of relatively large α1-Al particles formed during the slurry fabrication process and fine α2-Al particles formed in the die cavity. The macrosegregation in the form of the different ration of the primary α1-Al particles to secondary α2-Al particles in different positions of the rheocast component was observed. The relation between microstructural characteristics and thermal diffusivity was investigated by determining the local thermal conductivity in the rheocast component and ration of α1-Al particles to α2-Al particles. The results revealed that samples from the regions of the component with a high amount of α1-Al particles had a higher thermal conductivity. WDS measurement results pointed to that Si and Cu concentration in the α1-Al particles contained lower concentrations value compare to the α2-Al particles and therefore α1-Al particles has higher value for thermal conductivity.Silicon precipitation was confirmed using calorimetry and dilatometry to take place between 200 and 250°C. A linear relation between the fraction of Si precipitates formed and the increase in thermal diffusivity was obtained. Silicon in solid solution is shown to have a strong influence (negative) on thermal conductivity. When the silicon is precipitated by heat treatment the thermal conductivity increases. For an optimal combination of thermal and mechanical properties it is therefore important to use an ageing temperature above the temperature for Si precipitation.