7xxx系AlZnMgCu铝合金早中期时效强化析出相的研究

Study of the early & mid-stage hardening precipitates in a 7xxx AlZnMgCu aluminium alloy

用高分辨透射电镜(HRTEM)和显微维氏硬度计细致地研究分析了7xxx系AlZnMgCu铝合金的单级时效硬化和强化相析出行为,从不同的晶体学方向跟踪观察了硬化析出相形貌和晶体学演变规律。结果表明:在120℃保温时效该合金具有很明显的时效硬化特性,时效4 h硬度即为210 HV,时效20 h达到峰值227 HV;继续时效,存在一个较长时间的时效平台。GPII区在时效最初10 min后即迅速形成,与基体完全共格;η′相由GPII区发展而来,在时效8 h左右形成,也与基体完全共格;合金峰值时效是GPII区与η′相联合起主要强化作用。时效202 h,观察到初期的η相。没有观察到所谓{100}面上的GPI区。

The hardness and the early stage precipitates of an extruded Al-Zn-Mg-Cu alloy were investigated in detail by micro Vicker’ s hardness measurements and high-resolution transmission electron microscopy,following the morphology and crystallography evolution of the precipitates.It was found that the alloy has a strong age hardening behavior when annealled at 120 ℃.Aging for 4 h the hardness reaches 210 HV,and the alloy reaches its peak hardness of 227 HV after 20 h of aging.After peak aging,there is approximately a platform of hardness for a long time.GPII zones can form in 10 minutes of aging,completely coherent with the Al matrix.The η′ phase particles,transformed from GPII zones,were observed in the samples aged for 8 h.GPII zones and η′ phase are the main strengthening precipitates for peak aging.Aging for 202 h the η phase prime particles were observed.GPI zones were not observed.