焊后热处理对7055-0.1Sc铝合金搅拌摩擦焊接头的组织与力学性能的影响

Effect of Post-Weld Heat Treatment on Microstructures and Mechanical Properties of Friction Stir Welded 7055-0.1Sc Aluminum Alloy

对11 mm厚的7055-0.1Sc-T4铝合金板材进行搅拌摩擦焊接,研究了焊后热处理对接头的组织和力学性能的影响。结果表明,热处理前接头的硬度分布呈“W”形,接头前进侧和后退侧都有一个最低硬度区,强度系数为63.0%~73.8%,拉伸断口位于后退侧最低硬度区。焊后人工时效(120℃×24 h)热处理使焊核的硬度提高,但是不改变接头最低硬度区的硬度,对拉伸性能和断裂行为的影响甚微。焊后的固溶(470℃×1.5 h+水淬)+人工时效(120℃×24 h)(T6)热处理不改变低焊速接头的晶粒组织,但是使高焊速接头焊核区底部的晶粒异常长大;T6热处理使接头各区域原有的沉淀相溶解,重新生成细小均匀的η’和η(MgZn_(2))沉淀相,使其硬度显著提高;T6热处理使接头沿“S”线附近出现微小的孔洞、在拉伸过程中沿“S”线开裂、其抗拉强度比焊接态大幅度提高,达到母材强度的87%,但是其塑性严重降低。

7055-0.1Sc-T4 aluminum Al-alloy plates of 11 mm in thickness were firstly subjected to friction stir welding(FSW)and then the effect of post-weld heat treatment on the microstructure and mechanical properties of the FSW joints was investigated.The results show that for the as welded FSW joints,the hardness profiles distribution exhibited“W”shaped pattern with the low hardness zone(LHZ)on both the retreating(RS)and the advancing sides(AS),respectively.And the joints fractured at the LHZ on RS with the strength coefficient are 63.0%-73.8%.After the post-weld artificial aging at 120℃for 12 h(AA),the hardness of the nugget zone(NZ)increased but the hardness of the LHZ,tensile properties and fracture location were unchanged.Solution treatment at 535℃for 1.5 h+water quenching+artificial aging at 120℃for 12 h(T6)did not change the grain structure of the joint under low welding speed of mm/min,but caused the abnormal grain growth at the bottom of the NZ under high welding speed of 250 mm/min.Moreover,T6 heat treatment resulted in the dissolution of the original precipitates and the re-precipitation of fine and uniformη′andη(MgZn_(2))phases,and therefore significantly improved the hardness of the joints.The T6 joint cracked along the“S”line during tension with a seriously reduced plasticity and joint efficiency of 87%.