Defect susceptibility of sensile strength to microporosity variation in as-cast magnesium alloys with different grain sizes

Abstract

The variability in the tensile strength of as-cast AM60 and AZ91 alloys was investigated in terms of the defect susceptibility to the variation in grain size and microporosity. The microporosity was measured from the quantitative fractography analysis through scanning electron microscopy (SEM) observation on fractured surface after tensile test. The ultimate tensile strength (UTS) of both alloys can be characterized as a power law relationship to microporosity variation in terms of the defect susceptibility and maximum strength achievable in the defect-free condition. The defect susceptibility of tensile strength to microporosity variation is decreased remarkably with grain refinement. The defect susceptibility of AZ91 alloy to microporosity variation exhibits more sensitive dependence on the variation in grain size than AM60 alloy. Also, the dependence of UTS on the variation in grain size is described as a power law relationship for various levels of microporosity. The variation on effective void area fraction by the damage evolution of Mg17Al12 phase may introduce a practically significant decrease of load bearing capacity, less than by microporosity variation. The Hall-Petch relation of both alloys in the defect-free condition could be suggested as maximum values of friction stress and locking parameter.