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为了研究Sn对Mg-Al-Ca系合金热裂敏感性的影响,通过Clyne-Davies模型对MgAl_7Ca_1Sn_x(x=0,0.5,1,2)系合金的热裂敏感性进行预测。采用“T”型热裂模具,对MgAl_7Ca_1Sn_x系合金凝固过程中的温度、收缩应力信号数据进行采集,研究热裂纹萌生和扩展的相关信息。利用X射线衍射(XRD)和扫描电子显微镜(SEM)分别对MgAl_7Ca_1Sn_x系合金显微组织和热裂断口区域形貌进行观察。揭示合金的凝固最后阶段剩余液相分数,脆弱区域的凝固温度变化,第二相种类等因素对Mg Al_7Ca_1Sn_x系合金热裂倾向的影响;合金热裂倾向从大到小顺序为MgAl_7Ca_1Sn_1>MgAl_7Ca_1Sn_2>MgAl_7Ca_1Sn_(0.5)>MgAl_7Ca_1。其中,由于Mg Al7Ca1Sn1合金凝固温度区间最宽,脆弱区域的凝固温度变化最大,凝固最后阶段形成液膜最少,枝晶干涉点后析出的第二相阻碍枝晶间的补缩等多种原因使之热裂倾向最大。
In order to study the influence of Sn on the thermal cracking susceptibility of Mg-Al-Ca alloy, the thermal susceptibility of MgAl_7Ca_1Sn_x (x = 0,0.5,1,2) system alloys was predicted by Clyne-Davies model. The temperature and shrinkage stress data of MgAl_7Ca_1Sn_x alloy during the solidification process were collected by using “T” hot cracking tool, and the relevant information on the initiation and propagation of thermal crack was studied. Morphology of MgAl_7Ca_1Sn_x alloy microstructure and thermal cracking interface were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Revealing the influence of the residual liquid phase fraction in the final stage of solidification, the change of the solidification temperature in the weak region and the second phase species on the hot cracking tendency of Mg Al_7Ca_1Sn_x alloys. The hot tearing tendency of the alloys is MgAl_7Ca_1Sn_1> MgAl_7Ca_1Sn_2> MgAl_7Ca_1Sn_ (0.5)> MgAl_7Ca_1. Among them, MgAl7Ca1Sn1 alloy has the widest solidification temperature range, the largest change in the solidification temperature in the fragile region, the least amount of liquid film formed in the final stage of solidification, the second phase precipitated after the dendrite interference point hinders the interdendritic growth, and the like The hot crack the largest tendency.