-180℃深冷处理对7A99铝合金峰值时效强韧性能与析出行为的影响

Effect of Deep Cryogenic Treatment of -180℃ on Strength and Toughness Properties and Precipitation Behavior of 7A99 Aluminium Alloy

摘要:

对7A99超高强铝合金反向挤压板材采用T6峰值时效处理与-180℃冷热循环时效热处理(简称T6-DCT),通过XRD、TEM、HRTEM与3DAP研究-180℃深冷处理对7A99铝合金反向挤压板材强韧性能以及析出行为的影响。结果表明,-180℃冷热循环时效处理使得铝基体的晶格常数由由0.40551 nm 增至0.40626 nm,起到了一定的固溶强化作用；-180℃冷热循环时效处理后晶粒内部生成大量与基体非共格的η相,晶界处η相呈现断续分布并形成晶界无析出带,降低材料的拉伸强度；-180℃冷热循环时效处理促进基体中Zn和Mg元素原子的微观偏聚,导致了Zn和Mg元素的非均匀析出；-180℃深冷处理可以减小时效终态析出相的平均等效半径与析出密度,将等效半径由1.2 nm减小至1.14 nm,将析出密度由4.53×10₂₄/m₃降低至3.87×10₂₄ /m₃,削弱析出强化效果； -180℃冷热循环时效处理后合金的强韧匹配性能得到显著改善,强度略有降低,韧性显著提高。

Abstract:

Indirect extrusion of 7A99 ultrahigh-strength aluminium alloy was heat treated by T6 peak aging treatment and peak cold-heat cycle aging treatment of -180℃ (T6-DCT). XRD, TEM, HRTEM and 3DAP were applied to study the influences of T6-DCT treatment on the strength and toughness properties, precipitation behavior. The result shows that The lattice constant of Al matrix increases from 0.40551 nm to 0.40626 nm after T6-DCT, which plays a solid solution strengthening role. A large number of η phase generate in the grains, and the η phases at the grain boundaries are discontinuous, meanwhile the precipitation free zone is formed at the grain boundaries, which reduces the tensile strength. After T6-DCT treatment, the segreation degree of Zn and Mg increases, the precipitation ratio and distribution uniformity of precipitated phases decrease. The avearge equivalent radius of the precipitated phases changes from 1.2 nm to 1.14 nm after T6-DCT treatment, the density of the precipitated phases decrease from 4.53×10₂₄/m₃ to 3.87×10₂₄/m₃, which weaken the precipitation-strengthening. The strength and toughness improve significantly after T6-DCT treatment, which shows that the strength is slightly reduced and the toughness is improved remarkably.