Thixoformability and Microstructural Evolution of Al-Si-Cu Alloys

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Abstract Commercial aluminium casting alloys such as those from Al-Si-Cu family are widely used in the automotive industry because of their combinations of good fluidity and mechanical strength. Semisolid metal processing utilizing these alloys thus far has given products with better mechanical properties over those produced via traditional metal forming processes. However, there is still demand to widen the range of suitable alloys for the semisolid processing. One way of achieving this is by modifying the alloy compositions. Hence, modified alloys under this family were formulated and assessed. This paper reports results of the thermodynamics evaluation and microstructural evolution for one of these modified alloys, and comparing them with that of the commercially available A319 alloy. Data from Differential Scanning Calorimetry heating curves along the semi-solid range of the alloys were analysed and used as an approximation in determining their thixoformability. The work had demonstrated that the selected modified alloy is suitable for semisolid processing by having wider working window temperature, lower temperature sensitivity of liquid fraction and adequate solidification range. Both alloys, the modified and the commercial A319 alloys, were also successfully thixoformed and their microstructural features and quantitative measures obtained and compared. They both had given the shape factor and solid globule size within the acceptable values for the semisolid processing, i.e. of around 0.7-0.8 and 50-60 µm, respectively. However, in short, the modified alloy has shown better thixoformability characteristics than the commercial alloy.