Fabrication of Mg/Mg composite with sleeve-core structure and its effect on room-temperature yield asymmetry via bimetal casting-co-extrusion

A remarkable yield asymmetry at room temperature (RT), all the time, severely influenced the wide industrial applications of Mg alloys. Here, we report a novel approach entitled as bimetal casting-co-extrusion to reduce the yield asymmetry of Mg-3Al-1Zn (wt.%) alloy. The results show that when casting temperature is set as 760 degrees C, Mg-3Al-1Zn/Mg-1Y (AZ31/W1, wt.%) alloy with the sleeve-core structure can achieve a well metallurgical bonding. While casting temperature is below 760 degrees C, the contact surface of AZ31 and W1 billets takes place massive cracks, and even two alloys are unable to well connect. After co-extrusion, the interface zone of AZ31/W1 rod never has any cracks and holes. By TEM observation, the interface zone of similar to 1 mu m is composed of only alpha-Mg. With increasing the proportion of W1 core, the tensile and compressive elongation-to-failure values of AZ31/W1 rod apparently enhance, and the decrease in tensile strength and the consistence in compressive strength give rise to the improved yield asymmetry from 0.57 to 0.84 at RT. This is mainly attributed to the more activity of slip deformation in tension and the restriction of {10 (1) over bar2} extension twinning in compression. Therefore, this work offers an insightful opinion to improve the mechanical properties of Mg alloys, especially the yield asymmetry, by bimetal casting-co-extrusion method.