组织不均匀性对铝合金焊接区裂纹的影响

Effects of microstructural heterogeneity on crack behaviors in welding zones of aluminum alloy parts

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.