多道次MIG焊铝合金的焊接界面行为研究

Interface Behavior of Aluminum Alloy by Multipass MIG Welding

采用自制填充焊丝多道次MIG焊接8 mm厚铝镁合金板材,运用金相、扫描、X射线衍射以及电子背散射衍射(EBSD)等观测分析手段对焊接接头进行了微观组织分析。结果表明,焊缝区为典型的铸态组织,不存在明显的择优取向问题。但由于多道次焊接过程中焊接热循环的综合叠加效应,以及交界面两侧组织结构的相似性,相比较而言,靠近焊道交界处再加热粗晶热影响区的晶粒更倾向于外延生长,织构比细晶层和焊缝区更强烈一些,且晶粒长大明显,显微硬度更低,残余应力仅次于焊缝底端,成为焊接接头的一个薄弱环节。

Al-Mg alloy plates with 8 mm thickness were welded by multipass MIG welding with the self-made wires as filler material, and microstructure of the welded joint were examined by metallographic, scanning electron microscope（SEM）, X-ray diffraction and electron backscatter diffraction（EBSD）. The results show that the weld zone is typical casting microstructure with no obvious preferred orientation. Comparatively, grains are more inclined to epitaxial growth, and the texture in reheating coarse grain heat-affected zone is more obvious than fine grain layer and weld zone because of the comprehensive additive effect of welding thermal cycle and the structural similarity on the interface during multipass welding. Besides, the grain growth is more apparent, microhardness is lower, and the residual stress value is only second to weld bottom, which is the weakest link.