Mg对6061再生铝合金凝固特性和热裂行为的影响

Effect of Mg Addition on Solidification Characteristics and Hot Tearing Behavior of 6061 Recycled Aluminum Alloy

利用约束杆模具测试不同Mg含量(0.9%,1.0%,1.2%,1.4%和1.7%)对6061再生铝合金热裂敏感性(HTS)的影响,采用双电偶热分析法研究6061再生铝合金凝固行为、凝固过程特征温度等。试验结果表明,合金热裂敏感性随着Mg的加入先减小后增大;在Mg含量为1.2%时,合金有最小的热裂敏感性。Mg的加入促使初生α-Al、Al13Fe4和α-AlFeSi的析出温度降低,Mg2Si析出温度升高,合金凝固温度区间ΔT和易脆温度区间ΔTV均降低。6061再生铝合金热裂是合金在易脆温度区间ΔTV收缩和共晶反应收缩共同作用的结果。合金Mg含量低时,ΔTV比较大,凝固收缩应力大导致热裂敏感性大;随着Mg含量增加,ΔTV减小,凝固末期Mg2Si相增多,共晶转变收缩量大引起热裂。

The effect of Mg content(0.9%, 1.0%, 1.2%, 1.4%, 1.7%) on hot tearing sensitivity(HTS) of 6061 recycled aluminum alloy was systematically investigated by using the constrained rod casting mold. The solidification behavior and characteristic temperatures during the solidification of 6061 recycled aluminum alloy were studied by the double thermocouples thermal analysis. The experimental results show that the hot tearing sensitivity first decreases and then increases with increasing Mg content. The alloy has minimal hot tearing sensitivity when the Mg content is 1.2%. The addition of Mg can decrease the precipitation temperature of primary α-Al, Al13Fe4 and α-AlFeSi phase and increase the precipitation temperature of Mg2Si phase, thereby shortening the solidification temperature interval ΔT and the vulnerable region temperature interval ΔTV. The hot tearing sensitivity of 6061 recycled aluminum alloy is the result of the combination of shrinkage in the vulnerable region temperature range ΔTV and shrinkage in the eutectic reaction. When the Mg content is low, ΔTV is relatively large, and the sensitivity to hot tearing is large due to the large solidification shrinkage stress. As the Mg content increases, ΔTV decreases and the amount of Mg2Si phase increases at the end of solidification. Therefore, a large amount of eutectic transformation causes hot tearing.