通过分级淬火方法测定了7050铝合金的TTT曲线, 采用TEM和JMA方程等分析手段研究了固溶、等温淬火和时效过程中微观组织的演变规律及其动力学特性. 结果表明, 合金TTT曲线的鼻尖温度在330 ℃附近, 淬火敏感区间为300~380 ℃, 高温区(400~450 ℃)淬火敏感性低于低温区(210~270 ℃); 等温保温过程中过饱和固溶体主要析出以Al3Zr粒子为形核核心的片层状η平衡相及少量针状S相, 随保温时间延长析出相体积分数快速增加, 同时在晶界排列变得连续而粗化、无沉淀析出带(PFZ)宽化, 在远离鼻尖的温度下保温合金析出速率减慢, 在晶界排布连续化和粗化程度降低; JMA方程中反映析出相形态的常数n在0.50~0.65的范围内, 析出相特征以片层状相为主、针状相为辅.
7050 aluminum alloy is an important structural material widely used in aerospace industry with a high quench sensitivity. In this work, the time-temperature-transformation (TTT) curves of 7050 aluminum alloy were determined by interrupted quench method. The microstructure evolution and phase transformation kinetics during solid solution, isothermal quenching, ageing treatment were studied by TEM and JMA equation．The results show that the nose temperature of TTT curves is about 330 ℃, with the quench sensitivity range of 300~380 ℃. The quenching sensitivity of high temperature range of 400~450 ℃ is lower than that of low temperature range of 210~270 ℃. The laminar equilibrium η phases characterized with nucleus of Al3Zr particles and several needle-shaped S phases are the main precipitations of the supersaturated solid solution decomposes during isothermal holding process. With the increase of holding time, the volume fraction of precipitated phases rises quickly, which coarsen the grain boundary continuously and broaden precipitation free zone (PFZ). While holding far away from the nose temperature, the speed of precipitation slow down and the degree of continuity and coarsening of grain boundary decrease. The values of n in JMA equation vary from 0.50 to 0.65, indicating that the precipitations are mainly laminar precipitated phases and supplementarily needle-shaped phases.
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