Y含量对MgZn9YxZr0.5合金热裂敏感性的影响

基于Clyne-Davies模型,对MgZn9YxZr0.5(x=1,2,4,6,质量分数/%,下同)合金热裂敏感性(CSC)进行预测;采用X射线衍射(XRD)和扫描电子显微镜(SEM)分别对MgZn9YxZr0.5合金的显微组织与断口区域形貌进行观察,并采用"T"型热裂模具测试系统,采集MgZn9YxZr0.5合金凝固收缩应力随温度(或时间)的变化曲线。结果表明:CSC预测值与裂纹体积实测值具有相同的变化趋势,其热裂敏感性从高到低的顺序是:MgZn9Y1Zr0.5>MgZn9Y6Zr0.5>MgZn9Y2Zr0.5>MgZn9Y4Zr0.5;当w(Y)≤4%时,枝晶干涉点温度与热裂纹萌生温度随Y含量增加而降低,而当w(Y)=6%时,枝晶干涉点温度与热裂纹萌生温度随之升高。随Y含量不同,MgZn9YxZr0.5合金凝固过程中析出相类型、含量以及α-Mg枝晶倾向的改变被认为是影响晶界裂纹萌生、扩展和热裂的主要微观机制。

Effect of Y content on hot tearing susceptibility of MgZn9YxZr0.5 alloys

Based on the Clyne-Davies model,the hot tearing susceptibility(CSC)of MgZn9YxZr0.5 ( x =1,2,4,6,mass fraction/%) was predicted.The microstructure and morphology of hot tearing regions of the alloys were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the curves of solidification shrinkage stress with temperature (or time) of MgZn9YxZr0.5 alloys based on the "T" type hot tearing permanent-mold were collected.The results demonstrate that the predicted values of CSC are consistent with that of measured values of crack volume.The hot tearing susceptibility of the alloys from high to low is:MgZn 9Y 1Zr 0.5 >MgZn 9Y 6Zr 0.5 >MgZn 9Y 2Zr 0.5 >MgZn9Y4Zr0.5;the dendrite coherency temperature and the initial temperature of hot tearing decrease with the Y content increasing when w (Y) is not more than 4%.When w (Y) is 6%,the dendrite coherency temperature and the initial temperature of hot tearing increase.With the increase of Y content,the change of precipitation phase type,content and the dendrite tendency of α-Mg in the solidification process of MgZn9YxZr0.5 alloys is considered as the main micro-mechanism that affects crack initiation,propagation and hot tearing in grain boundary.