微量Ge对7056铝合金组织和淬火敏感性的影响

Effect of trace germanium on microstructure and quenching sensitivity of 7056 aluminum alloy

通过力学拉伸、末端喷淋淬火实验,结合金相观察、硬度测试、电导率测试、扫描电镜(SEM)和透射电镜(TEM)等测试分析方法,研究微量Ge元素对7056铝合金组织和淬火敏感性的影响。结果表明:添加微量Ge细化了合金晶粒,晶粒尺寸由137μm减小到114μm;添加微量Ge在晶界上形成了粗大的Mg_2Ge相,并抑制了T相的形成;与无Ge合金相比,添加Ge后无沉淀析出带(PFZ)宽度变窄,从190nm减小到90nm,同时晶界析出相尺寸减小;添加微量Ge显著降低了合金的淬火敏感性,合金淬透深度提高了约25%,这与慢速淬火时析出的η平衡相的数量和尺寸有关;Ge降低了合金中的空位浓度,η平衡相在缺陷处的非均匀形核及长大被抑制,时效后η′沉淀强化相数量增多,慢速冷却时合金强度下降程度减小,合金淬透性提高。

The effect of trace Ge on the microstructure and quenching sensitivity of 7056 aluminum alloy was studied by mechanical tensile and end quenching experiments, combined with some analysis methods such as metallographic observation, hardness test, conductivity test, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The results show that the trace element can refine the alloy grain sizes,the grain size is reduced from 137μm to 114μm;the addition of trace Ge formes coarse Mg 2Ge phase on the grain boundary and inhibits the formation of the T phase.In addition, compared with the Ge-free alloy, the width of the precipitation free zone of the Ge-bearing alloy becomes narrow, and is decreased from 190nm to 90nm, and the size of the precipitated phase at the grain boundary is reduced.The trace addition of Ge could reduce the quench sensitivity of alloy, increased the quenching depth of the alloy about 25%,which may be caused by the addition of Ge which changes the number and size of η equilibrium phase during slow cooling;the addition of Ge reduces the free vacancy concentration in the alloy, non-uniform nucleation and growth of the η equilibrium phase at the defect are suppressed, which increases the number of strengthening η′ precipitates after aging.Thus the drop in the strength is decreased during slow quenching,which increases the hardenability of the alloy.