Dependence of Room Temperature Tensile Properties on Volume Fraction of Discontinuous Precipitates in Cast AZ91 Magnesium Alloy

The objective of this study was to investigate the dependence of the room temperature tensile properties on the volume fraction of discontinuous precipitates (DPs) in a cast AZ91 magnesium alloy. In order to obtain various volume fractions of DPs, the solution-treated alloy was aged at 428 K for up to 48 h. The volume fraction of DPs increased from 0% to 72% with an increase in the aging time up to 24 h; for aging times longer than 24 h, discontinuous precipitation was substantially inhibited owing to the occurrence of significant continuous precipitation within the α-(Mg) grains. YS and UTS of the alloy increased with the volume fraction of DPs, whereas the elongation showed a reverse trend. A relatively rapid change in the tensile properties with increasing volume fraction of DPs up to ~40% was noted, which would be due to the reduction of the effective α grain size in response to the formation of DPs along the grain boundaries.