Microstructural evolution and failure mechanism of an extrusion welded aluminum alloy tube during hydroforming processing

During hydroforming of Al alloys, cracking often limits the production of specific frames for next-generation transportation vehicles. In this study, microstructural evolution and cracking behavior of an extrusion welded aluminum alloy blank tube were characterized to uncover the failure mechanisms during hydroforming process. Electron back-scattered diffraction, transmission electron microscope, and scanning electron microscope were employed to characterize the grains, textures, and local micro-crack sites. Experimental results demonstrated that grains in the welds region were significantly larger than those in the neighboring regions. Along the weld region, large grains typically with high-misorientation with respect to neighboring grains were identified as the preferred crack nucleation sites. Plastic incompatibility due to preferential yielding in the larger (softer) grains as compared to the surrounding finer (harder) grains is postulated as the origin for local strain localization that leads to cracking in the weld regions during hydroforming.