6005A-T6铝合金高速脉冲MIG焊焊补接头的组织和性能

Microstructure and properties of high-speed pulsed MIG repair welding joint of 6005A-T6 aluminum alloy

采用快速热启动工艺方法 RTS,研究轨道车辆用6 mm厚6005A-T6铝合金对接接头焊修后的组织和性能。结果表明,原始焊缝中的组织为树枝晶和等轴树枝晶,晶粒细小,焊缝组织由α-Al基体和Mg2Si、Al0.7Fe3Si0.3第二相组成;原始焊缝受焊补时的焊接热循环影响,α-Al基体晶粒开始粗化,三次补焊后,原始焊缝的微观组织恶化、晶粒粗化现象更为严重,有较多平衡相析出;在焊补焊缝与原始焊缝交界区域,随着焊补次数的增加,晶粒粗化现象愈加明显,界面区组织趋向恶化;焊前经80℃的RTS一次焊补,可较明显地减少常规补焊所产生的气孔缺陷,且焊补焊缝与原始焊缝交界区域的晶粒粗化现象不太明显,其微观组织优于常规一次焊补的;焊态、焊补态接头出现较明显的软化区,硬度值最低点出现在原始接头的热影响区;焊补接头的拉伸试样均呈45°切断,断口有明显的韧窝,为典型的韧性断裂,原始态及RTS一次焊补接头的强度系数达到0.6,且除三次焊补接头外,焊接(焊补)接头弯曲试验的弯曲角度为180°时,弯曲试样均无裂纹,接头塑性良好。

The microstructure and properties of the butt joint of repair welding of 6 mm 6005 A-T6 aluminum alloy plate for railway vehicle are studied by using the rapid thermal start-up technology(RTS). The results show that the microstructure of the original welds are dendritic crystal and equiaxial dendritic crystal,the grains are fine,and the microstructure of the weld is composed of α-Al matrix and Mg2 Si,Al0.7 Fe3 Si0.3 second phase;the original weld is affected by the weld thermal cycle of repair welding,the α-Al matrix grains begin to coarsening,and the microstructure deterioration and grain coarsening of the original weld are more serious after three times of repair welding,and more equilibrium phase precipitates out. At the common boundary of the repair welding weld and original weld,as the times of repair welding increases,the grain coarsening is more obvious and the microstructure of interface tends to deteriorate;Using once RTS(80 ℃) repair welding technology before welding,it can be more obvious to reduce the pores caused by the normal repair welding,and at the common boundary of repair welding weld and original weld,the grain coarsening is not obvious,its microstructure is superior to that of once normal repair welding. There are obvious softening zones in as-welded joint and repair welded joint,the minimum HV0.1 hardness value appears in the heat-affected zone of the original welded joint. The tensile specimens of repair welding joints break at 45°,and the fracture has obvious dimple,which is a typical ductile fracture. The strength coefficient of the original joint and the once repair welding joint by RTS is 0.6,and except the welded joint after three times repair welding,when the bending angle of welded joint is 180°,bending specimens have no cracks,and the plasticity of welded joint is good.