7020铝合金MIG焊焊接接头的组织与性能Microstructures and properties of MIG welded joint of 7020 aluminum alloy

采用显微硬度及拉伸力学性能测试、光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)、微区X射线衍射(Micro XRD)研究经ER5356焊丝金属极惰性气体保护焊(Metal inert gas, MIG)的7020铝合金厚板焊接接头的微观组织和力学性能。结果表明：7020铝合金MIG焊焊接接头的抗拉强度为268 MPa，屈服强度为231 MPa，伸长率为4.5%，焊接系数约为0.7；焊接接头的焊缝区为树枝状铸造组织；熔合区靠近焊缝一侧为柱状晶，靠近热影响区一侧为细小的等轴晶组织；热影响区为发生了部分再结晶的纤维组织；基材为明显的纤维组织。焊缝区的铸态组织导致其成为焊接接头最薄弱的位置，η′(MgZn₂)相粗化导致热影响区内离焊缝中心约30 mm的位置形成硬度较低的软化区。

The mechanical properties and microstructures of the welded joint of 7020 aluminum alloy welded using 5356 welding wire by the method of metal inert gas (MIG) welding were investigated by OM, SEM, TEM, micro X-ray diffraction, microhardness test and tensile mechanical properties test. The results show that the tensile strength, yield strength, elongation and welding coefficient of the welded joint are 268 MPa, 231 MPa, 4.5% and 0.7, respectively. The weld zone is characterized by dendritic structure, the columnar grains form in the fusion zone on one side of the welding seam as well as equiaxed crystal on the other side. The fibrous organization is obviously found in the base metal, and in the heat affected zone, the recrystallization occurs. The weld zone is the weakest position in the welded joint due to the dendritic structure. The soften zone in the heat affected zone, approximately 30 mm away from the centre of welding seam, forms as a result of η′(MgZn₂) coarsening.

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