7075–O铝合金搅拌摩擦焊接头微观组织与力学性能

Microstructure and Mechanical Performance of 7075-O Aluminum Alloy Friction Stir Welded Joints

时效硬化态7075铝合金搅拌摩擦焊接头塑性较低,给进一步变形加工带来困难。本文采用3 mm厚的7075–O铝合金板进行搅拌摩擦对接焊,研究焊接速度对接头组织和强塑性的影响,为获得高塑性的搅拌摩擦接头提供解决方案。结果表明,7075–O铝合金接头焊核区为细小的等轴晶粒,随焊接速度的增加,焊核区平均晶粒尺寸呈先减小后缓慢增加的趋势,当焊接速度为40 mm/min时,焊核区晶粒尺寸最小,约为1.96μm。不同焊接速度下接头横截面显微硬度呈“凸”形分布,接头区域发生明显硬化,其中焊核区硬度最高,约为145HV。7075–O铝合金搅拌摩擦焊工艺窗口较宽,焊接速度在20~80 mm/min范围内接头强度均高于母材强度,焊接件伸长率达母材的82%,采用7075–O铝合金不仅能够克服时效硬化态7075铝合金搅拌摩擦焊接头的软化问题,而且能够获得更高的伸长率。接头弯曲试验结果表明,7075–O铝合金搅拌摩擦焊接头能够承受更大的弯曲角度,极限弯曲角达105°,具备更加出色的塑性变形能力。

The age-hardened AA7075 in the friction stir welding(FSW)joints exhibits lower plasticity,posing challenges for further deformation processing.In this study,this paper employed a 3 mm thick AA7075–O plate for stir friction butt welding,investigating the impact of welding speed on the joint microstructure and strength-ductility,aiming to provide solutions for achieving highly ductile FSWed joints.The results reveal that the weld nugget zone(NZ)in the AA7075–O joint consists of fine equiaxed grains.With an increase in welding speed,the average grain size(AGS)in the weld NZ initially decreases and then gradually increases.At a welding speed of 40 mm/min,the smallest AGS in the weld NZ is approximately 1.96μm.The microhardness distribution across the transverse section of the joint shows a convex shape at different welding speeds,indicating significant hardening in the joint region.The weld NZ exhibits the highest hardness,reaching approximately 145HV.The process window for FSW of AA7075–O is broad,with joint strength exceeding the base material(BM)strength at welding speeds within the range of 20–80 mm/min.The elongation of the welded specimen reaches 82%of the BM.The use of AA7075–O not only overcomes the softening issue in the age-hardened AA7075 FSWed joints but also yields a higher elongation.Bending test results demonstrate that the FSWed joints of AA7075–O can withstand larger bending angles,with a maximum bending angle reaching 105°,indicating superior plastic deformation capabilities.