Effect of feedstock geometry on the semisolid processing of Al–Si–Cu–Mg alloy

Abstract

Shaping a metal by thixoforming involves feedstock preparation and reheating. Proper procedure and accurate processing criteria for thixoforming are required to provide a quality product. Appropriate parameters are crucial in assessing the capabilities of this thixoforming process. In this study, the effect of different billet geometry of Al–Si–Cu–Mg alloy on microstructure and mechanical properties were investigated. The billet with different geometries of height-to-diameter ratio (h0/d0 = 3.2 and h0/d0 = 0.8) was utilized through the cooling slope casting technique and thixoformed after being heated into compression press. The results indicate that low h0/d0 ratio produced the finest grain size for the α Al solid phase (≈52.8 ± 5.1 μm), best shape factor and complete die filling. By contrast, high h0/d0 ratio produced coarser grain size for the α Al solid phase (≈62.2 ± 6.1 μm), insufficient die filling, cold shut and shrinkage porosity defect. Moreover, the thixoformed billets with the lower h0/d0 ratio exhibited higher tensile stresses. The ultimate tensile strength, yield strength, and elongation to fracture of the thixoformed h0/d0 ratio 3.2 improved at 183 MPa, 163 MPa, and 1.6%, respectively, whereas the values of the thixoformed h0/d0 ratio 1.25 alloy were 206 MPa, 193 MPa, and 2.5%, respectively