Al­Mg­Si与Al­Zn­Mg合金异质焊接接头力学性能和微观结构的关系

摘要

通过硬度测试、拉伸试验以及疲劳试验对Al­Mg­Si (T5)与Al­Zn­Mg (T4)异质焊接件的力学性能进行了测试，并通过扫描电镜(SEM)，背散射电子衍射技术(EBSD)，能谱仪(EDS)以及透射电镜(TEM)对焊接接头的微观结构进行观察。结果表明：异质焊接件出现了明显的软化区，在焊接热循环作用下，该区经过类似过时效处理，出现了粗大的β′相和U2相，导致其强度远远小于两母材的强度，并且拉伸断裂发生于软化区。疲劳试验结果显示，疲劳断裂发生于Al­Mg­Si母材一侧的熔合线处。这是由于Al­Mg­Si母材一侧的熔合区强度低，并且存在大量脆性尖锐的富硅相，在循环载荷作用下容易萌生疲劳裂纹。%The mechanical properties of an Al­Mg­Si­T5 and Al­Zn­Mg­T4 dissimilar weld joint were tested through hardness test, tensile test and fatigue test, and the microstructure was investigated by scanning electron microcopy (SEM), backscattered­electron diffraction (EBSD), energy dispersive spectrometer (EDS) and transmission electron microscopy (TEM). The results show that a softened zone, which seems to experience an over­aged treatment because of the weld heat, appears in the dissimilar weld joint. And the tensile test specimen fails in the softened zone, where coarseβ′phase and U2 phase exist. It is found that the fatigue testing specimen fractures approximately at the fusion line, which is near the heat affected zone of Al­Mg­Si base metal. The combined effect of the brittle Si­rich particles and the low strength leads to the fatigue crack initiation at this place.