Easy dismantling and separation of friction stir-welded steel and aluminum by foaming

With the growing trend toward using multi-materials to realize lightweight structures, friction stir welding (FSW) has attracted attention as a dissimilar metal joining technology. In dissimilar metal joining, dismantling and separation technologies for joined components at the time of disposal are also required. In this study, we attempted to facilitate the separation of FSW joints between an SS400 plate and an Al-Si-Cu ADC12 die-casting alloy plate by heating and foaming the joints and by reducing the strength of the joints. From the vertical cross sections of the samples in their FSW direction after joining, it was found that the foaming agent powder could be mixed near the joining interface of the ADC12 plates by FSW simultaneously with the joining process. The four-point bending test of the joined samples showed that the joining strength of the as-welded samples with powder added was equivalent to that of the as-welded samples without powder added or that of the ADC12 base material. Heating the ADC12 parts mixed with the foaming agent could foam the area near the joining interface. From the four-point bending test of the obtained samples, it was found that the samples with foamed areas fractured at the foamed area near the joining interface, and SS400 and ADC12 can be easily separated, whereas both as-welded samples fractured at the joining interface or at the ADC12 base material. The samples with foamed areas show markedly reduced maximum load and energy required for separation compared with as-welded samples. Consequently, it was shown that easy separation by foaming the joint can be realized with low load and energy by applying the FSW precursor fabrication method.