Mechanical Properties of Magnesium Alloys Produced by the Heated Mold Continuous Casting Process

Investigation of the tensile and fatigue properties of cast magnesium alloys, created by the heated mold continuous casting process (HMC), was conducted. The mechanical properties of the Mg-HMC alloys were overall higher than those for the Mg alloys, made by the conventional gravity casting process (GC), and especially excellent mechanical properties were obtained for the Mg₉₇Y₂Zn₁-HMC alloy. This was because of the fine-grained structure composed of the α-Mg phases with the interdendritic LPSO phase. Such mechanical properties were similar levels to those for conventional cast aluminum alloy (Al_84.7Si_10.5Cu_2.5Fe_1.3Zn₁ alloys: ADC12), made by the GC process. Moreover, the tensile properties (σ and ε_f) and fatigue properties of the Mg₉₇Y₂Zn₁-HMC alloy were about 1.5 times higher than that for the commercial Mg₉₀Al₉Zn₁-GC alloy (AZ91). The high correlation rate between tensile properties and fatigue strength (endurance limit: σ_l) was obtained. With newly proposed etching technique, the residual stress in the Mg₉₇Y₂Zn₁ alloy could be revealed, and it appeared that the high internal stress was severely accumulated in and around the long-period stacking-order phases (LPSO). This was made during the solidification process due to the different shrinkage rate between α-Mg and LPSO. In this etching technique, micro-cracks were observed on the sample surface, and amount of micro-cracks (density) could be a parameter to determine the severity of the internal stress, i.e., a large amount to micro-cracks is caused by the high internal stress.