Mechanical behaviour of cast magnesium alloys

The tensile mechanical properties of pressure die cast magnesium alloys were investigated with a focus on the following areas: Property variations between alloys AZ91D, AM60 and AS21; The effects of section thickness on properties (1 mm - 10 mm); The effects of strain rate (0.01-1 s(-1)) on properties; and Comparison of pressure die cast properties to sand-cast and thixomolded properties. Differences in tensile properties and strain rate sensitivity were observed between alloys. AM60 and AS21 showed similarly shaped flow curves, although AM60 exhibited significantly greater ductility. The flow curves of AZ91D alloys were shifted to higher stresses compared to AM60 and AS21. Strain rate had a noticeable effect on the work hardening of AS21, but no significant effect on AM60, or AZ91D, which suggests a strain rate sensitivity dependence on aluminium content. Section thickness effects were variable, although the tendency was for a shift in the flow curves of thinner samples to higher stress levels. The property variations between AZ91 castings produced by pressure die-casting, sand casting and thixomolding were significant, especially at low strains. Much of the differences could be accounted for on the basis of differences in the fineness of the microstructure.