Effect of Ca Content on Hot Tearing Susceptibility of Mg-4Zn-xCa-0.3Zr (x=0.5, 1, 1.5, 2) Alloys

Mg-Zn-Ca alloy has a good development prospect in biomedical alloy. However, its development is restricted by large hot tearing susceptibility. Herein, the influence of Ca addition on the hot tearing susceptibility (HTS) of Mg-4Zn-xCa-0.3Zr (0.5, 1, 1.5, and 2 wt%) alloys has been studied by using thermal analysis and numerical simulation software, Procast. The "Clyne-Davies" hot tearing prediction model was improved, and Cracking Susceptibility Coefficient (CSC) was recalculated to highlight the physical significance of the model. The hot tearing zone was observed via optical microscopy and scanning electron microscopy, and the phase composition was analyzed with X-ray diffraction. The results of numerical simulations suggest that the Hot Tearing Indicator (HTI) tended to decrease with increase in Ca addition. However, the experimental results reveal that with the increase in Ca addition, the hot tearing susceptibility of the alloys first decreased with Ca addition up to 1.5 wt% and then displayed a slight increase with the addition up to 2.0 wt%. The SEM images and experimental results reveal that the thickness and ability to resist solidification shrinkage stress of the liquid membrane, quantity of the second phases, and feeding ability were all enhanced with the increase in Ca addition, thereby reducing the HTS of Mg-4Zn-XCa-0.3Zr alloys. When the Ca addition reached 2.0 wt%, the brittle calcium-containing phase forms at the grain boundary, which reduces the high-temperature strength of the matrix and the ability to resist the solidification shrinkage stress of the alloy, resulting in an increase in HTS. Therefore, when the Ca addition was 2.0 wt%, the simulation results were different from the experimental results.