Effects of yttrium on microstructure and mechanical properties of Mg-Zn-Cu-Zr alloys

The effects of yttrium addition on microstructure and mechanical properties of as-cast Mg-6Zn-3Cu-0.6Zr-xY(x=0,0.5, 1.0,1.5 and 2.0,mass fraction,%)(ZCK630+xY for short in this study)alloys were investigated by means of OM,XRD and SEM. The results show that the average grain size of Mg-Zn-Cu-Zr magnesium alloy is effectively reduced(from 57μm to 39μm)by Y addition.The analysis of XRD indicates the existence of I-phase(Mg3Zn6Y)and W-phase(Mg3Zn3Y2)in ZCK630 alloys with Y addition.The ultimate tensile strength of ZCK630 alloys is significantly deteriorated with increasing Y addition,which is possibly related to the continuous networks of intergranular phases and the increase of W-phase.     

Cu元素对挤压剪切ZK60合金组织性能及织构演变的影响

采用金属型铸造方法制备ZK60及ZK60+1.0Cu(质量分数,%)合金,并对两种合金进行均匀化热处理与两步复合挤压剪切成形。利用OM、SEM、EDS、XRD、EBSD、TEM及室温拉伸-压缩实验研究了挤压剪切合金的显微组织、相组成及力学性能。结果表明：向ZK60合金中加入1.0Cu后,合金α-Mg基体中出现三元MgZnCu相。ZK60+1.0Cu合金成形区平均晶粒尺寸为1.56 μm,其远小于ZK60合金(4.68 μm),且MgZnCu相附近存在着尺寸为300±45 nm的亚晶粒。相比于ZK60合金,ZK60+1.0Cu合金成形区拥有着较弱的{0001}基面织构,且织构基极和挤压方向(ED)夹角发生转变,造成ZK60+1.0Cu合金成形区中存在着更多易于{0001}<11\bar{\mathrm{2}}0>基面滑移启动的动态再结晶(DRX)晶粒。ZK60+1.0Cu合金成形区的拉伸及压缩强度明显高于ZK60合金,其主要归因于晶界强化,而拉伸伸长率的降低和硬质MgZnCu相带来的微孔聚集有关。     

铸造Mg-Zn-Cu-Zr合金的生长孪晶行为(英文)

在铸造Mg-Zn-Cu-Zr合金100°C时效过程中观察到生长孪晶,采用光学显微镜和透射电子显微镜表征生长孪晶的形貌和位向。结果表明:在铸态和固溶态的Mg-Zn-Cu-Zr合金中未发现生长孪晶,仅在时效态合金中出现{10ī2}型生长孪晶。Zn含量和热处理工艺显著影响其孪生行为。最后,从空位角度讨论此类生长孪晶可能的生长机制。