1420铝锂合金搅拌摩擦焊接头的组织演变及力学性能

Microstructural characteristics and mechanical properties of friction stir welding joint of 1420 aluminum-lithium alloy

铝锂合金采用搅拌摩擦焊技术进行焊接可有效提高焊接接头的各项力学性能指标。采用SEM、TEM、EBSD等试验方法,对10mm厚1420铝锂合金搅拌摩擦焊焊接接头的显微组织形貌、织构类型、析出相以及接头硬度分布情况进行分析,讨论了组织结构对接头力学性能的影响。研究结果表明:焊接接头的焊核区、热机影响区以及热影响区呈现不同组织形貌;焊核区由均匀细小的再结晶组织构成,热机影响区板条组织发生弯曲变形,热影响区在焊接热循环作用下晶粒发生粗化,其组织形貌与母材基本保持一致;焊核区主要织构类型为变形织构S{123}<634>和再结晶织构R{124}<211>,含量分别为18.9%和18.1%,热机影响区和热影响区的主要织构类型与焊核区相同,含量稍有变化,母材中变形织构Copper{112}<111>为主要织构类型,体积分数为16.9%;合金的析出相为δ′相,即Al3Li,相的含量沿母材、热影响区、热机影响区方向递减,直至在焊核区内消失;焊缝的硬度值整体高于母材,并按照焊核区—热机影响区—热影响区—母材方向逐渐减少,焊接前进侧硬度始终小于后退侧硬度;试验中析出相对合金力学性能的影响较小,晶粒度是影响合金硬度的主要因素。

The mechanical properties of weld joint in Al-Li alloy could be enhanced by using the friction stir welding （FSW）. Microstructure, textures, precipitate phase, hardness distribution of 10 mm thick weld joint in 1420 Al-Li alloy after FSW were studied by using the SEM, TEM, EBSD methods, etc. Furthermore, interactions between microstructures and mechanical properties were discussed. The results show that the microstructures of three zones in the joint are all different, and they all vary from matrix. The stir zone is composed of recrystallization textures. The lath structures and grains distort in thermo-mechanically affected zone. Because ofthe heat effect arising from FSW, grains in heat affected zone are forced to become bigger than those in matrix, but the shape is similar to that of the matrix. The types of major texture in the stir zone are S{123}〈634〉 , R{124}〈211〉, and the volume fraction of texture is 18.9% and 18.1 % , respectively. The main textures and their contents in thermo-mechanically affected zone and heat affected zone are similar to those in stir zone. But, in base metal （BM）, Copper{ 112} 〈111〉（13.5%） become the initial texture and volume fraction is 16. 9% meanwhile, the contents of other textures, such as S and R, have a sharp decrease in BM. In this study, the δ′ precipitate, known as Al3Li, is the only precipitate of 1420Al-Li alloy. According to matrix, heat affected zone, thermo-mechanically affected zone and stir zone in order. The content ofδ′ precipitate decreases gradually, and finally, vanishes in the stir zone. The hardness of the joint is lower than that in matrix, and gradually decreases along the direction of the stir zone, thermo- mechanically affected zone, heat affected zone, and matrix direction. Also, the hardness of advancing side is always lower than that of retreating side. In this study, δ′precipitate has little influence on microhardness of the weld joint, but the grain size will be the main influence factor.