异种铝合金零倾角搅拌摩擦焊接头组织性能研究

Study on microstructure and properties of zero⁃inclination friction stir welding joints of dissimilar aluminum alloy

采用零倾角搅拌摩擦焊工艺对6061T6和2024T4铝合金进行焊接,研究了不同焊接速度焊接接头的组织和力学性能。结果表明:零倾角搅拌摩擦焊接接头截面中部为焊核区,两侧为热机械影响区、热影响区和母材,焊核区可见明显的“S”线。接头的母材组织为长条状α铝晶粒,焊核区为细小的等轴晶,热机械影响区呈弯曲变形的晶粒,热影响区组织与母材组织类似。接头截面硬度分布呈“W”形,最低硬度位于热机械影响区和热影响区结合处。随着焊接速度的增大,焊核区硬度值呈增大趋势,同时接头软化区范围逐渐缩小。接头的抗拉强度随着焊接速度的增大呈先增后减的趋势,而伸长率却呈现逐渐降低的趋势。焊接速度为900 mm/min时的强度最高,为263.62 MPa,接头断口为典型的韧窝状断口。

In this paper,the zero⁃inclination stir friction welding process was used to weld 6061T6 and 2024T4 aluminum alloys,and the microstructure and mechanical properties of the welding joints at different welding speeds were studied.The results show that the center of the zero⁃inclination stir friction welding joint is stir zone(SZ),on both sides of SZ are thermo⁃mechanical affected zone(TMAZ),heat affected zone(HAZ)and base material(BM),a clear“S”line presented in the SZ.The microstructure of BM of the joint is elon⁃gatedαaluminum grains,the SZ is composed of fine isometric grains,the TMAZ is bending deformation grains,and the metallographic of the HAZ microstructure is similar to that of the BM.The hardness distribution of the joint cross⁃section is in a“W”shape,the lowest hard⁃ness is located at the junction of TMAZ and HAZ.With the increase of welding speed,the hardness of the SZ shows an increasing trend,while the range of the joint softening zone is gradually reduced.The tensile strength of the joint first increases and then decreases with the increase of welding speed,while the elongation gradually decreases.The highest strength is 263.62 MPa at the welding speed of 900 mm/min.The fracture morphology of the joint is the typical tough nest fracture.