Thermodynamic Modelling of Al-Si-Cu Alloys for Semisolid Metal Processsing

Thixoforming is a new technology in producing near net-shape products in semisolid state. This process can reduce macrosegregation, porosity and involve low forming forces. Currently, there are a few grades of aluminum alloys such as A319, A356 and A357 commonly used in semi-solid metal processing. Therefore, there is a demand to widen the range of aluminum alloys specially tailored for semisolid metal processing. This study discusses the thermodynamic modelling to predict changes in the properties of aluminum alloy A319 expecially when the content of alloying elements such as copper, manganese and iron are varied in order to fulfill the criteria of semisolid metal processing. All the calculations in the present work were performed using Java-based Material Properties (JMatPro) commercial software. Thermodynamic calculation based on Scheil’s equation is used to determine solidification temperature range (ΔT), liquid fraction sensitivity (dfL/dT) and processing window temperature (ΔT^30/50). The thermodynamic calculation shows that the solidification temperatures have decreased from 130 to 113°C while the eutectic temperatures have increased from 510 to 515°C when the wt.% of copper, manganese and ferum were increased. The liquid fraction sensitivity is reduced from 0.017 to 0.007°C^-1 and the processing window temperature is reduced from 26 to 24°C. Eutectics binary reactions occurred between 30 and 50% liquid fraction for all alloy groups. Phase diagram is used to identify the formation of intermetallic phase compound such as β-Al5FeSi and Al2Cu in the alloys. The results indicate the suitability of these modified alloys as potential materials for semisolid processing.