基于焊接速度的6082铝合金FSW接头组织与力学性能调控研究

Research on the Microstructure and Mechanical Properties of 6082 Aluminum Alloy FSW Joints based on Welding Speed

为研究焊接速度对6082铝合金搅拌摩擦焊(FSW)接头微观组织和力学性能的影响,并建立基于焊接速度的FSW接头组织与性能调控规律。通过金相观察、电子背散射衍射(EBSD)分析、硬度测试、室温拉伸和弯曲试验等手段,对四种不同焊接速度(500 mm/min、750 mm/min、1000 mm/min、1250 mm/min)下FSW接头的微观组织和力学性能进行表征。结果表明,随着焊接速度的增大,FSW接头的微观组织发生显著变化。焊核区(NZ)发生连续动态再结晶,形成细小的再结晶晶粒组织,其平均晶粒尺寸从3.8μm减小至2.3μm,再结晶分数从83%减小至57.3%;热机影响区(TMAZ)发生部分动态回复和部分动态再结晶,晶界处出现少量细小等轴晶粒,晶内形成大量亚晶组织。亚结构比例和小角度晶界比例显著增加,分别为69.2%和60.1%;受焊接热影响,热影响区(HAZ)相比母材区(BM)的晶粒尺寸略有增大,再结晶程度和晶界角度分布与母材相似。力学性能方面,随着焊接速度增大,FSW接头硬度最低值从72.3 HV增大至81.2 HV,焊接系数从74.7%提升至89.0%,热影响软化区明显缩小,但在1250 mm/min焊速下FSW接头背弯试样产生裂纹。基于焊接速度的调控模式,1000 mm/min焊接速度下FSW接头具有最优的力学性能。

The purpose of this study is to investigate the effects of welding speed on the microstructure and mechanical properties of 6082 aluminum alloy friction stir welding(FSW)joints,and to establish the regulation rules of FSW joint microstructure and properties based on welding speed.Metallographic observation,electron backscatter diffraction(EBSD)analysis,hardness testing,room temperature tensile and bending tests were used to characterize the microstructure and mechanical properties of FSW joints at four different welding speeds(500 mm/min,750 mm/min,1000 mm/min,1250 mm/min).The results show that with the increase of welding speed,the microstructure of FSW joints changes significantly.In the weld nugget zone(NZ),continuous dynamic recrystallization occurs,forming fine recrystallized grain structures,with the average grain size decreasing from 3.8μm to 2.3μm and the recrystallization fraction decreasing from 83% to 57.3%;In the thermomechanically affected zone(TMAZ),partial dynamic recovery and partial dynamic recrystallization occur,with a few fine equiaxed grains appearing at the grain boundaries and a large number of subgrain structures forming inside the grains.The proportion of substructure and the proportion of small-angle grain boundaries increase significantly,reaching 69.2% and 60.1% respectively;Due to the welding heat effect,the grain size in the heat-affected zone(HAZ)increases slightly compared to the base metal zone(BM),and the degree of recrystallization and grain boundary angle distribution are similar to those of the base metal.In terms of mechanical properties,with the increase of welding speed,the minimum hardness of FSW joints increases from 72.3 HV to 81.2 HV,the welding coefficient increases from 74.7% to 89%,and the heat-affected softening zone is significantly reduced.However,cracks occur in the back-bend specimen of FSW joints at a welding speed of 1250 mm/min.Based on the welding speed control mode,the FSW joint has the best mechanical properties at a welding speed of 1000 mm/min.