焊接工艺对6082-T6铝合金FSW接头微观组织与力学性能的影响

Effect of welding parameters on microstructure and mechanical properties of 6082-T6 aluminum alloy FSW joint

利用光学显微镜(OM)、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)、硬度和室温拉伸等方法,研究焊接工艺对厚度为5 mm的6082-T6铝合金搅拌摩擦焊接头微观组织与力学性能的影响。研究结果表明:在相同焊接速度下,随着搅拌针旋转速度的增加,焊核区(NZ)晶粒长大,再结晶程度提高,第二相数量增多且分布更均匀,焊核区的硬度增加;而热影响区(HAZ)晶粒长大、第二相粗化,硬度严重下降。低旋转速度时,硬度最低值位于焊核区和热机影响区(TMAZ)之间,接头硬度分布曲线呈"U"形,高旋转速度时,焊核区硬度较高,热影响区严重软化,其硬度低于焊核区,接头硬度分布曲线呈"W"形。随着旋转速度的增加,低旋转速度组FSW接头抗拉强度逐步增高,高旋转速度组FSW接头抗拉强度先增高,后降低。当旋转速度为1 400 r/min时,FSW接头抗拉强度最好,为271.63 MPa,焊接系数达到82.12%。

The effect of welding parameters on microstructure and mechanical properties of friction stir welded joints of 6082-T6 aluminum sheet of 5 mm in thickness was investigated by optical microscope,transmission electron microscope,electron backscatter diffraction,tensile test and hardness test.The results show that with the increase of the rotational speed at constant travel speed,the grains in nugget zone(NZ)grow up,the degree of recrystallization becomes higher,the number of the second phase increases and its distribution becomes more homogeneous,which results in the increase of the hardness of NZ.But the hardness of heat affected zone(HAZ)decreases because of the grains growth and serious coarsening of the second phase.When the rotational speed is low,the lowest hardness is between NZ and thermomechanically affected zone(TMAZ),and the hardness distribution profile of FSW joints is just like“U”.When the rotational speed is high,the hardness of NZ is higher than that of HAZ,and the hardness distribution profile of FSW joints is just like“W”.With the increment of the rotational speed,the tensile strength of the FSW joint of the low rotational speed group increases gradually,but the tensile strength of the FSW joint in the high rotational speed group increases first and then decreases.When the high rotational speed is 1 400 r/min,the best tensile strength of the joint is 271.63 MPa and the welding coefficient reaches up to 82.12%.