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

Okayasu M., Wu S., Tanimoto T., Takeuchi S.

Archives of Foundry Engineering

2016

Vol. 16, iss. 4

208--216

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.