稀土元素钇对ZM5合金组织的影响

Effect of Rare Earth on Microstructure of Mg-8.5AL-0.5%Zn Alloy

在ZM5合金熔体中分别加入不同量的稀土元素钇,经过不同处理,利用光学显微镜和扫描电镜以及能谱分析,研究了稀土元素钇对ZM5合金组织的影响规律。实验结果表明,向ZM5合金中添加稀土元素Y的质量分数达2%时,合金的显微组织明显改善。X衍射和金相照片显示ZM5合金铸态组织为αMg固溶体和沿晶界分布的网状βMg17AL12组成,固溶处理后Mg17AL12弥散在基体中,而加入稀土元素Y的ZM5合金由α(基体)、Mg17AL12和颗粒状MgY等相组成。经固溶处理后网状Mg17AL12相完全溶解,只留下热稳定性较高的MgY以及析出相Al2Y等。扫描电镜显示ZM5合金拉伸试样断口是解理断裂的断口形态,而加入稀土元素Y的ZM5合金拉伸试样断口是沿晶断裂+准解理断裂的混合断口形态。究其原因为加入稀土元素Y后,熔体中生成了与镁基体共格的强化相MgY和弥散的析出相改变了断口形貌。

Effect of Yttrium on cast Mg-8.5%Al-0.5% Zn alloy (ZM5 alloy) is studied using X-ray diffraction, SEM, microscope and energy spectrum. The results show that with addition of 2% Yttrium the microstructure of the alloy is significantly improved. X-ray diffraction and microscope study reveals that for ZM5 alloy the microstructure consists of α-Mg solid solution with network and/or Mg17Al12 phase dispersed along grain boundary; after solution treatment, Mg17Al12 phase is almost dissolved in Mg matrix. For the alloy containing yttrium the microstructures consists α-Mg solid solution, network β-Mg17Al12 and MgY; after solution treatment, the Mg17Al12 is totally dissolved in α-Mg matrix, there still exist the rare earth compounds MgY and newly precipitated Al2Y phases. SEM reveals that the fracture morphology of ZM5 alloy is cleavage fracture; while the yttrium treated ZM5 ally is mixed morphology of cleavage and Intergranular fracture. It is suggested that with yttrium addition strengthening MgY phase coherent with magnesium matrix and newly precipitated Al2Y in the melt, which changes the fracture morphology.