Effects of silicon on microstructure, fluidity mechanical properties, and fracture behaviour of Mg-6Alalloy

To investigate the effects of silicon, additions of 0.3, 1, and 1.5% were m ade to an Mg-6A1 master alloy. Two types of Mg2Si particle morphology were observed, namely, square-like and 'Chinese script'. Silicon improved the fl uidity, hardness, and microhardness, but decreased the impact toughness of Mg-6A1 alloy. High cooling rate led to fine morphology and high hardness. T est bars were fabricated by casting the alloys into a permanent mould and a s cast tensile tests were carried out at ambient temperature and 150 degree sC. Silicon was detrimental to the ambient temperature tensile properties. However, additions of 0.3 and 1%Si improved the tensile properties at 150 d egreesC. The fracture behaviour of the alloys, which predominantly assumed brittle cleavage and/or qnasicleavage failure, was examined by SEM and opti cal microscopy. The fragile interfaces between the magnesium matrix and int ermetallic particles often provided the crack propagation sites.