Study On The Microstructure And Creep Behavior Of ECAPed Mg-Zn-Si Alloys

Mg and its alloys are lightest metal structural materials, meanwhile, their advantages also include high specific strength and specific rigidity, good damping property, electromagnetic interference resistance and diecastibility. Mg recently has become the fn'st choice light materials for automotive and electronic industry. The strength and creep property of the present commercial Mg alloys however sharp drop after the service temperature is above 125℃, which restrict the field of application of Mg alloys.Researchers have developed RE magnesium alloys to solve the problem. As a scarce resource, RE is expensive, which limits its general application. So scholars have put eyes on Si which has a excellent high temperature performance and relative lower price. In the as-cast alloys, course Chinese character-shaped and long-strip Mg2Si phase can cut crack matrix easily, reduce the mechanical properties, so its application is limited. By producing severe plastic deformation, equal channel angular pressing (ECAP) can refine the matrix and the second phase effectively and achieve the purpose of improving mechanical properties of materials. Accordingly, the subject of ZK31 magnesium alloy and ZK60 magnesium alloy and the Si with different content and different ECAP passes would be taken. Afterwards, the microstructures and the creep behavior of the magnesium alloys were investigated in order to seek the way to improve performance of high temperature creep greatly by ECAP technology.The experimental results show that the coarse Chinese script-like Mg2Si precipitates are refined to fine polygonal shape particles and redistributed dispersedly after ECAP. The creep resistance was greatly enhanced after ECAP. The results show thatα-Mg has been significantly refined after 8-pass ECAP and coarse Chinese script-like Mg2Si precipitates are refined to fine polygonal shape particles and redistributed dispersedly. The grain-size of samples of 8-pass ECAPed is uniformer than 4 times evenly, and Mg2Si is redistributed dispersedly. As a strengthening phase, Mg2Si improve the mechanical properties and the high temperature creep properties.Large lumps Mg2Si and poor performance of alloys would be hade if ZK31 magnesium alloy by adding 5% Si.It can be offset that the separate of Si by a certain amount of Si was added to ZK magnesium alloys and after appropriate passes. The mismatch of Mg2Si and matrix is at a lesser degree, and Mg2Si has a high melting point. Therefore, the high temperature creep performance of alloy was improved significantly. The creep resistance was greatly enhanced by Si. The Creep time of the ZK60+4%Si specimen is better than it of ZK31+4%Si specimen. It may be due to the improvement of the alloy Zn.In addition, we have studyed the creep mechanism of ZK31+4%Si magnesium alloy and magnesium alloy ZK60+4%Si magnesium alloy and their ECAPed samples. The results show that the creep mechanism was dislocation creep.