钕添加及铸锭均匀化退火对ZK20镁合金组织与性能的影响

Effects of Nd addition and homogenizing annealing of ingot on microstructure and properties of ZK20 Mg alloy

利用金相显微镜(OM)、扫描电镜(SEM)和万能材料试验机,对ZK20和ZK20+0.5Nd镁合金不同温度均匀化退火后的组织以及挤压态合金的力学性能进行研究。退火温度分别为603、633、663、693K,保温时间均为10h。结果表明:均匀化退火使铸锭中的Mg-Zn和Mg-Nd-Zn合金相不断固溶到基体中,同时枝晶偏析大幅度降低;与未均匀化相比,ZK20+0.5Nd合金均匀化退火后挤压,挤压态塑性有较大幅度提高,而强度并没有降低;稀土Nd细化ZK20合金晶粒,使均匀化退火提高挤压态合金塑性的作用更加明显,增强均匀化退火效果。对于ZK20合金,663K,10h是最优的均匀化退火工艺;对于ZK20+0.5Nd合金,693K,10h是较合适的退火工艺。

The effects of homogenizing annealing of ingot on as-annealed microstructure and as-extruded mechanical properties of ZK20 and ZK20＋0.5Nd magnesium alloy were investigated by room tensile test,optical microscopy and scanning electron microscopy.The annealing temperatures were 603,633,663,693 K,separately,and the holding time was 10 h.The results show Mg-Zn and Mg-Nd-Zn compounds observed in the cast ingot disappear gradually with increasing annealing temperature,and the dendritic segeration decreases dramatically.The elongation of as-extruded ZK20＋0.5Nd alloy after homogenizing annealing is higher than that of the alloy without annealing while its strengh remains unchanged.The Nd addition can refine the grain and improve the ductility of as-extruded alloy,and the effect of homogenizing annealing on the elongation of ZK20 alloy is enhanced as a result.It can be concluded that the better homogenizing annealing process are 663,10 h for ZK20 and 693,10 h for ZK20＋0.5Nd.