热变形参数对Al-Zn-Mg-Cu铝合金淬火敏感性的影响

Effect of hot deformation parameters on quenching sensitivity of Al-Zn-Mg-Cu aluminum alloy

采用热压缩试验、光学显微镜和透射电子显微镜研究热变形参数对Al-Zn-Mg-Cu铝合金淬火敏感性的影响。结果表明:随Z参数值增加,硬度先增加后减小,再结晶程度和淬火敏感性则先减小后增加,在ln Z为28.44～28.62的范围内,室温水淬硬度值最大,为188.8HV,而再结晶分数最小,为3.5%,空气淬火较室温水淬火硬度下降率最小,为2.5%。根据Z参数值范围确定淬火敏感性最小区间对应的热变形加工制度为变形温度387～434℃、变形速率0.23～1.23 s_(-1),变形温度443～450℃、变形速率0.61～1.77 s_(-1)。淬火敏感性是由于微观组织中的Al_3Zr粒子、晶界及亚晶界析出粗大η相导致过饱和固溶体溶度降低所致。不同的热变形制度会导致组织中Al_3Zr粒子相界、晶界及亚晶界含量不同。当三者协同影响最小时,合金具有最小的淬火敏感性。随着Z参数值增加,Al_3Zr粒子尺寸及与基体的错配度与再结晶程度趋势相同,尺寸与错配度越小析出粗大η相尺寸越小,面积分数越低。

The effects of hot deformation parameters on the quenching sensitivity of Al-Zn-Mg-Cu aluminum alloy were studied by hot compression test, OM and TEM. The results show that, when Z-parameter increases, the hardness increases firstly and then decreases, while the degree of recrystallization and quenching sensitivity decrease firstly and then increase. The hardness of RT water quenching is the highest (188.8HV). The recrystallization fraction is the smallest (3.5%), when lnZ ranges from 28.44 to 28.62, at the same time, the decline of minimum hardness after air quenching reaches 2.5% comparing with that of RT water quenching. According to the Z parameter, it can be determined that the corresponding thermal deformation institution to the minimum zone of quenching sensitivity are temperature 387-434 ℃, deformation rate 0.23-1.23s^-1 and temperature 443-450 ℃, deformation rate 0.61-1.77s^-1. The auenching sensitivity is caused by micro particles as Al3Zr, the coarse η phase precipitates on grain boundary and subgrain boundaries, leading to solubility of supersaturated solid solution decreasing. Different thermal deformation institution will result in different Al3Zr phase boundaries, grain boundaries and sub-grain boundaries. The less the synergy effect is, the better the quenching sensitivity is. With the Z-parameter increases, the grain size of Al3Zr particles and the mismatch of that with the matrix show the same tendency with the recrystallization degree, the lower the grain size and mismatch are, the smaller the area fraction of recrystallization is.