组织不均匀性对铝合金焊接区裂纹的影响

摘要

本文利用扫描电子显微镜电子背散射衍射（ EBSD）技术研究了一种Al⁃Zn⁃Mg合金焊接区微观组织结构不均匀性对裂纹萌生和扩展的影响。实验显示裂纹在粗晶区和细晶区的界面处萌生，沿着晶界扩展。小角度晶界对沿晶裂纹的扩展有阻碍作用，产生“闭合效应”。穿晶裂纹在遇到大角度晶界时，扩展路径会发生偏转。在部分再结晶区域，裂纹更倾向避开变形晶粒，沿着再结晶晶粒之间的晶界扩展。如果在外力作用下，迫使裂纹穿过形变晶粒，将导致解理断裂的断口形貌。%In the present work, electron back scattering diffraction was employed to investigate the effects of microstructural heterogeneity on the initiation and propagation of a crack in typical welding zones of aluminum alloy parts. The results show that when the welding zones consist of heterogeneous microstructure regions of large⁃size grains and small⁃size grains, a crack trends to initiate at and then propagate along the borders between the region with large grains and that with small grains. It is also shown that low⁃angle grain boundaries may impede the propagation of intergranular crack tips by causing crack closure whereas large⁃angle grain boundaries can change the propagation path of a transgranular crack. For partially recrystallized microstructure regions where the microstructure of recrystallized equiaxial grains and that of deformed elongated grains coexist, a crack usually propagates along the borders of these heterogeneous microstructure regions.