Comparison of high cycle fatigue behaviors of Mg-3Nd-0.2Zn-Zr alloy prepared by different casting processes

The influences of casting defects on the fatigue behaviors of Mg-3Nd-0.2Zn-Zr magnesium alloys were studied using porosity-free low pressure sand mold casting bars (LPS) and gravity permanent mold casting ingots (GPM) containing a few porosities. The results show that porosities have detrimental effect on the fatigue strength and life. The samples failed from the porosities show much lower fatigue strength and life in comparison with those failed from slip bands and twin bands. The fatigue strength increases with the yield strength increasing. Fatigue strength of the porosity-free T6-treated specimens made by LPS is determined by the threshold stress for basal slip, which is related to the interactions among slip bands, precipitates and grain boundaries. Both grain boundary constraints and cyclic deformation irreversibly caused by twinning are the crucial factors influencing the fatigue strengths of the porosity-free T4-treated specimens made by LPS.