Influence of diffusion mechanisms in aluminium solid-state welding processes

The film theory of solid-state bonding states that welding requires close contact to be established between aluminium substrates, and that this is achieved by applying a strain parallel to the interface-cracking the oxide layers-and a normal contact stress, micro-extruding the substrates through the cracks. Once contact between the substrates has occurred, the inter-atomic forces of attraction cause a weld to form. Existing research, however, suggests that diffusion mechanisms contribute to the bond strength as well. In order to understand the importance of diffusion mechanisms, in this study AA1050 solid-state welds are created under varying temperatures and process times. In the experiments, two adjacent aluminium strips are stretched in a tensile testing machine and simultaneously squeezed in a perpendicular direction by two heated flat tools, pushed together by hydraulic pancake rams. Shear tests determine the strength of the resulting welds. The results are used to explain the importance of diffusion mechanisms in creating strong bonds