采用硬度测试、拉伸实验、XRD分析和TEM观察等方法, 研究了一种新型形变热处理(预时效+冷轧变形+再时效)对时效硬化型铝合金微观组织和力学性能的影响. 结果表明, 这种形变热处理不仅能够大幅度提高6061铝合金强度, 还能使其保持良好塑性. 经过优化处理(180 ℃, 2 h欠时效+75%压下量冷轧变形+100 ℃, 48 h再时效), 6061铝合金的抗拉强度和屈服强度分别为560和542 MPa, 延伸率为8.5%. 微观组织观察表明, 合金强度的提高来源于析出强化、位错强化、位错胞强化和高Taylor因子的综合作用; 相对于冷轧状态, 延伸率的改善则与再时效过程中强化相的再析出和位错的轻微回复有关.

In order to improve mechanical properties of age-hardenable Al alloys markedly based on the conventional processing conditions, a novel thermo-mechanical treatment, which was consisted of pre-ageing, cold-rolling and re-ageing, was proposed in the present work. The effects of the thermo-mechanical treatment on microstructure evolution and mechanical properties of the 6061 Al alloy were investigated further by hardness measurement, tensile testing, XRD, TEM and HRTEM. It was shown that both the increased strength and elongation of the 6061 Al alloy were achieved simultaneously by the thermo-mechanical treatment. Especially, after the combination of under-ageing at 180 ℃ for 2 h, cold-rolling with the thickness reduction of 75% and re-ageing at 100 ℃ for 48 h, the ultimate tensile strength and yield strength of the alloy were 560 and 542 MPa, respectively, and the elongation was about 8.5%. The strength increment of the thermo-mechanically treated 6061 Al alloy was attributed mainly to the additional introduction of dislocation strengthening, dislocation cell strengthening and high Taylor factor value except for precipitation strengthening as compared to the conventional peak-aged alloy. Furthermore, the improved elongation of the thermo-mechanically treated 6061 Al alloy was mainly due to both the re-precipitation of strengthening precipitates and slight recovery of dislocations during re-ageing, which increased the accumulation ability of dislocations during the tensile deformation.