Study On Semi-Continuous Casting Mg-Zn-Ca Alloy And Its Deformation Behavior Of Hot Extrusion

Mg-4.50wt.%Zn-1.13wt.%Ca alloy was produced through semi-continuous casting. Solidification simulation of as-cast alloy was calculated with Pandat 8. The alloy was extruded under different conditions in order to investigate the effect of extrusion conditions on the microstructure and mechanical properties of Mg-Zn-Ca alloy. XRD analysis was used to study the texture of as-extruded alloy. Through tensile tests in different orientations, anisotropy of mechanical properties of the as-extruded alloy was investigated.Solidification simulation indicates that as-cast alloy is mainly composed ofα-Mg and Ca2Mg6Zn3. Ca2Mg6Zn3 precipitates through eutectic reaction, i.e. Lα-Mg+Ca2Mg6Zn3 at 388oC. Experimental results are almost consistent with the calculation, indicating that Pandat 8 is a powerful tool for designing Mg alloy. Due to the coarse grain and the Ca2Mg6Zn3 distributing in grain boundaries, as-cast alloy shows poor mechanical properties with the ultimate tensile strength and elongation of 110MPa and 1.6%, respectively.Homogenization has detrimental effect on extrudability and prompts dynamic recrystallization. After subjected to extrusion, the as- homogenized alloy exhibited obvious different mechanical properties with the as-cast alloy. The as-cast alloy is extruded with different temperatures and ratios in order to investigate the effect of extrusion parameters on the microstructure and mechanical properties. The grain of as-extruded alloy is refined greatly due to dynamic recrystallization. Basal texture weakens with increasing the extrusion temperature. The alloy extruded at 350oC shows poor tensile strength and higher elongation compared with that extruded at 300oC. The intensities of basal texture have no large differences under difference extrusion ratios. But the strength with ratio 16 is higher than that of 8, indicating that basal texture is not the most important factor to influence the strength. And the phenomenon is related to grain refinement and precipitates.The mechanical anisotropy of the as-extruded alloy was investigated by tensile tests in different orientations. The Mg-Zn-Ca alloy shows obvious anisotropy due to the intensive basal texture. This is related to different deformation mechanisms during tensile tests. When tilt angle is 0o and 22.5o, the yield is controlled by prismatic slip. And when the angle is 45o, the yield is caused by basal slip. When the angle is 67.5o and 90o, twinning is the dominant deformation mechanism. Twins could interact with dislocation, resulting in stress concentration. As a result, the elongation become poorer with increasing the tilt angle.