Effects of silicon on microstructure, fluidity, mechanical properties, and fracture behaviour of Mg–6Al alloy

Abstract

To investigate the effects of silicon, additions of 0.3, 1, and 1.5% were made to an Mg–6Al master alloy. Two types of Mg₂Si particle morphology were observed, namely, square­like and ‘Chinese script’. Silicon improved the fluidity, hardness, and microhardness, but decreased the impact toughness of Mg–6Al alloy. High cooling rate led to fine morphology and high hardness. Test bars were fabricated by casting the alloys into a permanent mould and as cast tensile tests were carried out at ambient temperature and 150°C. Silicon was detrimental to the ambient temperature tensile properties. However, additions of 0.3 and 1%Si improved the tensile properties at 150°C. The fracture behaviour of the alloys, which predominantly assumed brittle cleavage and/or quasicleavage failure, was examined by SEM and optical microscopy. The fragile interfaces between the magnesium matrix and intermetallic particles often provided the crack propagation sites.