Elevated temperature mechanical properties and microstructures of high pressure die cast magnesium AZ91 alloy cast with different section thicknesses

This paper investigates the influence of variations in the microstructure of high pressure die cast AZ91 on the elevated temperature mechanical properties of the alloy. Thinner-walled high pressure die castings show an improvement in elevated temperature strength, ductility and creep resistance. Further improvements to the creep resistance were achieved by ageing the alloy prior to creep testing. It appears that an increased proportion of fine grained ‘skin’ region in the thinner castings contributed to the improved properties. Also, it appeared that the presence of supersaturated solute Al in the eutectic α-Mg contributes to the poor creep properties, probably due to the microstructural instability. Final failure is associated with the growth of voids either from porosity in the alloy or nucleated from discontinuous precipitates.