Er对Mg-5Zn-x Er镁合金热裂敏感性的影响

Effects of Er on Hot Cracking Susceptibility of Mg-5Zn-x Er Magnesium Alloys

采用优化的RDG (Rappaz-Drezet-Gremaud)热裂模型预测了Mg-5Zn-x Er (x=0.83、1.25、2.5、5,质量分数,%)三元多相合金的铸造热裂敏感性,并利用"约束杆"钢模铸造(CRC)实验评价了该合金的热裂敏感性。结果表明,优化的RDG热裂模型可准确地预测Mg-5Zn-x Er镁合金的热裂敏感性:随着Er含量的增加,合金的热裂敏感性呈先增加后降低的趋势,当Er含量为2.5%时合金的热裂敏感性最高,当Er含量为5.0%时合金的热裂敏感性最低,与实验结果相一致。对铸件凝固曲线、相组成、微观组织等进一步分析表明,当Er含量提高至2.5%时,合金凝固过程发生包晶反应生成I相的同时消耗了液相,并且扩大了合金的凝固温度区间,使合金的热裂敏感性上升;Er含量继续提高至5.0%时,合金在凝固过程中发生L→α-Mg+W的共晶反应,凝固温度区间减小,有利于凝固后期枝晶间裂纹的补缩,显著降低了合金的热裂敏感性。

Mg-Zn-Er casting magnesium alloys have good properties,such as high specific strength,high specific stiffness and remarkable temperature creep properties.Current researches mainly focused on the phases and mechanical properties at room and high temperatures.However,the effect of Er on hot cracking susceptibility of Mg-5 Zn-x Er magnesium alloys was barely studied.In this work,a modified RDG(Rappaz-Drezet-Gremaud)model for predicting the hot cracking susceptibility of Mg-5 Zn-x Er(x=0.83,1.25,2.5,5,mass fraction,%)ternary alloys was proposed,which considered the effects of phase and solidification temperature range on the hot cracking susceptibility of the multiphase alloys.And,the hot cracking susceptibility was evaluated by the experiment of constrained rod casting(CRC).The results indicated that the modified RDG model could accurately predict the hot cracking susceptibility of Mg-5 Znx Er magnesium alloys.The hot cracking susceptibility increased with the addition of Er up to 2.5%,and Mg-5 Zn-2.5 Er alloy showed the maximal hot cracking susceptibility;when the addition of Er increased to5.0%,Mg-5 Zn-5 Er alloy exhibited the minimal hot cracking susceptibility.The calculated results were consistent with the experimental ones.Further analysis on the casting solidification curves,phases and microstructures showed that I-phase precipitated by peritectic reaction during solidification of Mg-5 Zn-2.5 Er alloy depleted liquid phases and extended the solidification temperature range of the alloy,leading to the hot cracking susceptibility increasing.The Mg-5 Zn-5 Er alloy underwent eutectic reaction of L→α-Mg+W during solidification,which reduced the solidification temperature range.Meanwhile,this process was beneficial to feeding the interdendritic hot cracking in the terminal period of solidification,which significantly decreased the hot cracking susceptibility of Mg-5 Zn-5 Er alloy.