焊后时效对7046铝合金搅拌摩擦焊接头力学性能的影响

Effect of Post Aging on Mechanical Properties of Friction Stir Welded 7046 Aluminum Alloy

对厚度为3.5 mm的7046铝合金挤压板材进行搅拌摩擦焊接并对焊接接头进行人工时效,研究了焊后时效对接头力学性能的影响。结果表明,焊接接头时效前的硬度分布大致呈"W"形,抗拉强度为406.5 MPa,焊接系数为0.8,拉伸时在后退侧热影响区与热机影响区的过渡位置出现断裂,此处的硬度值最低,断裂面上有大量的韧窝;进行120℃×24 h时效后,接头的热影响区、热机影响区和焊核区的硬度都显著提高,母材区的硬度变化不大,硬度分布大致呈"一"形,抗拉强度大幅度提高到490 MPa,焊接系数达到0.96,拉伸时在焊核区中心断裂,断裂面有大量的沿晶裂纹。时效后接头区域的晶内GPI区转变成具有更好强化效果的η′亚稳相,使接头的硬度和强度提高;与其它区域相比,焊核区中晶界η相的分布更连续,晶界处无沉淀析出带的体积分数更大,因此容易成为拉伸时的断裂位置。

Extruded sheets of 7046 aluminum alloy of 3.5 mm in thickness were subjected to friction stir welding(FSW)and then post aging treatment.The hardness profile of the FSW joint exhibits a"W"shape and the ultimate tensile strength is 406.5 MPa with a welding coefficient of 0.8.During tensile test fracture appears at the minimum hardness zone,which is the transition area between the heat affected zone(HAZ)and the thermal-mechanically affected zone(TMAZ)on the retreating side.There are a lot of dimples on the fracture surface.After aging at 120℃for 24 h there is little change in the hardness of the base metal(BM)but the hardness of the HAZ,TMAZ and nugget zone(NZ)increase apparently,which is more or less the same as that of the BM.The ultimate tensile strength increases significantly up to about 490MPa with the welding coefficient increasing to about 0.96.Fracture appears at the NZ and there are a lot of intergranular cracks on the fracture surface.After aging,the GPI zones within grains of the FSW joint transform intoη'metastable phase with better strengthening effect,leading to higher hardness and strength.ηphase tends to be more continuous at grain boundaries and there is a higher volume fraction of precipitates free zones near grain boundaries in the NZ than other regions,therefore,fracture tends to occur in the NZ during tensile test.