Li对Al-Zn-Mg-Cu合金微观组织的影响

Effects of Li on Microstructure of Al-Zn-Mg-Cu Based Alloys

分别熔炼了含Li和不含Li的2种7XXX系合金,合金经过双级时效(120℃+160℃)后,利用TEM研究了第二级时效峰值状态时的微观组织。结果表明,2种合金的沉淀强化相均是η′(MgZn_2)。与不含Li合金相比,含Li合金具有更细小的析出强化相和更窄的沉淀无析出带(PFZs)。

Two kinds of Al-Zn-Mg-Cu based alloys with and without Li addition were prepared by ingot metallurgy. The specimens were undertaken by a two-steps aging after solid solution quenching, namely at 120degreesC for 3 h followed by 160degreesC for different hours. The microstructures of peak-aged specimen during the second step aging were examined by transmission electron microscopy (TEM). The results showed that the precipitates with hardness peak for both alloys were normally eta' phase(MgZn2). However, by contrast with the Li-free alloy, the precipitation phases were much fine in dimension, and the precipitation free zones (PFZs) were much narrow for the Li-adding alloy. The reason could be probably attributed to the role of Li:trapping vacancies, as a consequence, the diffusion of Zn and Mg atoms was restrained, then, the growth of eta' phase was slowed down. The results were discussed with a theory of aging kinetics.