Effects Of Ce On Microstructures And Properties Of ZM21 Magnesium Alloy

Wrought magnesium alloy, which has a higher strength, better ductility than the cast magnesium alloy, applies to the structural parts with requirements for different conditions. Therefore, the development of high plasticity of magnesium alloys meets the requirements of the long-term trends. It has pratical significance to improve the mechanical properties and processing performance of wrought magnesium alloys by alloying, grain refinement and other means, and to develope the new inexpensive plastic wrought magnesium alloys.ZM21 magnesium alloy with different mass fraction of rare earth Ce is prepared by adding MgCe master alloy to the ZM21 alloy. The influence of the Ce on microstructures and properties of ZM21 was investigated, and amount of the Ce added into ZM21 alloy which has been optimized. The main conclusions of this paper are as follows:By adding Ce, both the tensile strength and the elongation of ZM21 as cast alloy fall down followed by arising step. When the content of Ce is 0.39%,the tensile strength is higher than ZM21; when the content of Ce is 0.57%, the elongation is barely reach to the level of magnesium alloy ZM21. With an increase of the content of Ce element,hot compression deformation resistance of the alloy increases.Besides a small amount of Ce and Zn dissolve in the matrix,most of them gather in dendritic gap in form of second phase. With the increase of Ce, the content of Zn and Ce dissolved into the matrix decreases. Meanwhile, the second phase increases gradually and finally forms a network structure, which becomes thicker due to serious segregation.After homogenizing at 420℃for 10h,the dendrite segregation in alloy dissolves into the matrix effectively. The Mn-phase precipitates from the matrix after homogenizing. In addition to Mg and Mn phase, there are also Mg17Ce2 and CeMg12 phase that are the high temperature and stable phase in alloy that contains Ce. Effect of homogenization temperature on grain of the extrusion product is not significant, that is, homogenization temperature has little effect on grain size of extrusion products.After extrusion, tensile strength and yield strength have been greatly improved, especially the yield strength from less than 80Mpa up to more than 160Mpa. 2 # ~5 # deformed alloys can reach 180Mpa, and 5 # alloy can be close to 200Mpa. Plasticity of alloys with Ce additiona is higher than 1 # alloy, especially for 4 # alloy which can reach 24%.After extrusion, with the increase of Ce content, grains of ZM21 magnesium alloy become finer. When the Ce content reaches 0.39%, the refining effect is stable.Most of the rare earth elements Ce in ZM21 magnesium alloy forms Mg17Ce2 and CeMg12 phase or exists in grain boundaries, strengthening the grain boundary. They are broken and dispersed in the matrix alloy during the process of plastic deformation. Ce stabilizes the fine grain structure and impedes grain boundary sliding during plastic deformation to impact plasticity. When the Ce content reaches 0.39%, the two aspects of Ce on plasticity balances, and the plasticity will not improve.