7N01-T5铝合金搅拌摩擦焊接头微区软化行为及控制  

Micro-softening behavior and its control of 7N01-T5 Al alloy friction stir welded joint

作　　者：刘建 陈辉刚[2] 韦景勋 李建 张哲睿 李颖 何长树 LIU Jian;CHEN Hui-gang;WEI Jing-xun;LI Jian;ZHANG Zhe-rui;LI Ying;HE Chang-shu(CRRC Qingdao Sifang Locomotive Vehicle Co.Ltd,Qingdao 266111,China;Jihan Railway Qingdao Locomotive Project Supervision Unit,Qingdao 266111,China;School of Materials Science and Engineering,Northeastern University,Shenyang 110819,China;Key Laboratory for Anisotropy and Texture of Materials,Northeastern University,Shenyang 110819,China)

机构地区：[1]中车青岛四方机车车辆股份有限公司,山东青岛266111 [2]济南铁路局青岛机车车辆监造项目部,山东青岛266111 [3]东北大学材料科学与工程学院,辽宁沈阳110819 [4]东北大学材料各向异性与织构教育部重点实验室,辽宁沈阳110819

出　　处：《轻合金加工技术》2021年第11期58-67,共10页Light Alloy Fabrication Technology

基　　金：兴辽英才计划项目(XLYC1808038)。

摘　　要：可时效强化型铝合金搅拌摩擦焊(FSW)接头焊核区(NZ)及热影响区(HAZ)由于受到焊接热循环作用,析出相粒子组态特征发生转变,成为接头的薄弱区。本试验采用不同焊接参数对10 mm厚7N01-T5铝合金进行双面搅拌摩擦焊接,分析了接头微区软化形成机制,并探究了焊接热输入、焊后自然时效以及焊接过程中施加局部冷却对接头微区软化行为的影响。结果表明:不同焊接速度条件下,接头显微硬度分布均为"W"型,NZ及HAZ的硬度值低于母材的,出现微区软化现象,高热输入条件下,接头微区软化现象更为明显。NZ软化的形成是由于在热-机械作用下母材中η′析出强化相粒子发生溶解所致。NZ可以通过焊后自然时效,GP区的再次脱溶析出提高硬度。自然时效30 d后,NZ的显微硬度可恢复至母材的硬度值。HAZ软化的形成是由于该区域在焊接热循环作用下析出了粗大的η相,导致该区域的时效强化能力减弱,自然时效后该区域仍是接头性能最薄弱区。在焊接过程中对HAZ施加局部冷却,能有效改善HAZ微区软化。施加局部冷却后,接头焊态显微硬度最低值(76.4 HV)比空冷焊接条件下接头显微硬度最低值(67.7 HV)提高了8.7 HV;自然时效30 d后,施加局部冷却的接头平均屈服强度、抗拉强度和伸长率分别为231 N/mm^(2)、336 N/mm^(2)和9.25%,屈服强度和抗拉强度分别提高了4.2%和8.6%。The precipitates in the nugget zone(NZ) and heat-affected zone(HAZ) of the age-strengthening aluminum alloy friction stir welding(FSW) joint are transformed by the thermal cycling, inducing the NZ and HAZ to become weak areas of the joint. In this test, the 10 mm thick 7 N01-T5 Al alloy was subjected to double-sided friction stir welding under different welding parameters. The micro-softening mechanism of the joints was investigated;and the influences of heat input, post-natural aging, and local cooling on the micro-softening behavior of the joints during the welding process were explored. The results show that the microhardness distribution curves of the joints under different welding speed conditions were W-shaped. The microhardness values of NZ and HAZ were lower than that of the base metal. Local softening behavior occurred in the NZ and HAZ of the joints, which was more obvious under the condition of high heat input. The softening phenomenon occurred in the NZ was due to the dissolution of the strengthening particles with the thermo-mechanical effects, which can be solved by post-natural aging through the reprecipitation of the GP zones to increase hardness. After 30 days of natural aging, the microhardness of NZ can be restored to the value of the base metal. Alternatively, the softening phenomenon in the HAZ was because of the precipitation of the large size of η phase owing to the thermal cycling, thus decreasing the age-strengthening ability of this region. Therefore, even after natural aging, this region was still the weakest region of the joint. Local cooling applied to the HAZ during the welding process could effectively suppress the local softening problem in the HAZ. The lowest microhardness value(76.4 HV) of the joint welded under the local-cooled condition was 8.7 HV higher than that of the joint welded under the air-cooled condition(67.7 HV). After 30 days of natural aging, the average yield strength, tensile strength and elongation of the joint with local cooling were 231 N/mm^(2), 336 N/mm^(2)

关 键 词：7N01-T5铝合金 搅拌摩擦焊 显微组织 力学性能 自然时效 局部冷却 

分 类 号：TG453.9[金属学及工艺—焊接] TG146.21[一般工业技术—材料科学与工程]