本文利用硬度(HV)、光学显微镜和透射电镜(TEM)系统地研究了微量Cu(0.19％)对Al-5.0Zn-1.7Mg合金的沉淀过程、临界形核温度(T_c~′)和显微组织参数的影响。结果表明,Cu能促进合金均匀沉淀,提高T_c~′和HV,但没有细化晶粒和抑制再结晶的作用。但在本实验所采用的时效条件下(120—200℃),含Cu合金的晶界沉淀相(GBP)、基体沉淀相(MPt)和无沉淀带(PFZ)均比无Cu合金小,并且随时效时间的延长和温度的升高呈单调的变化。Cu的这种影响可用空位四面体与溶质原子结合成的复杂集团是GP区晶核的模型来说明。
The effect of a trace of Cu, about 0.19 wt-％, on the precipitation, the critical nucleation temperature, T_c~′, as well as the microstructural parameters of a commercial purity Al-S.0Zn-1.75Mg alloy has been studied by means of hardness test, optical microscopy and TEM. It was resulted that Cu, in contrast to Cr, is an element by which its homogeneous precipitation is promoted, the T_c~′ is raised from 150—160℃ to 170—180℃ and the hardness is increased, but the grain size is not yet refined and the recrystallization is not yet inhibited. Under the experimental condition of 120—200℃ aging, the grain boundary precipitation, the matrix precipitation and the precipitation-free zone of the Cu-contained alloy are minor to that of Cu-free one. All of these alteration may be monotoneous with elongation of aging time and elevation of aging temperature. Thus, it was proposed that the effect of Cu added on the precipitation and the structural parameters may he explained by a nucleation model which a complex cluster of the vacancy-tetrahedron combined with the segregated solute atoms, such as Zn, Mg and Cu, acts as a nucleus of GP zone.
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