Effect of different Mg content on microstructure and mechanical properties of thixoformed Al-Si-Cu-Mg alloys

This study investigated the effect of Mg content on microstructure and mechanical properties of thixoformed Al-Si-Cu-Mg alloys. Two sets of alloys containing 1.0 and 1.5 wt.% Mg with non-dendritic structure were fabricated using the cooling slope casting technique. The samples were then analysed under energy dispersive X-ray spectroscopy, optical microscopy, and scanning electron microscopy. The thixoformed samples underwent mechanical testing, such as tensile and hardness tests. The results have shown that various types of intermetallic phases were formed in the alloys, which contributed to the enhancement of the mechanical properties of the thixoformed alloys. An increment of 1.5 wt.% Mg contributed to an increment towards the tensile strength. The T6 heat treatment on the alloys has also recorded noticeably better mechanical properties. The ultimate tensile strength (UTS), yield strength (YS) and elongation to fracture of the heat-treated sample with 1.0 wt.% Mg reached a 270 MPa, 230 MPa and 2.9%, respectively, whereas for the 1.5 wt.% Mg sample, the tensile strength (UTS), yield strength (YS) and elongation to fracture were increased to 320 MPa, 270 MPa and 2.5% respectively. The alloys exhibited a mix-mode fracture behavior, where cleavage and dimple fractures were seen clearly on the samples.