Joining aluminum and steel today is still challenging. The large difference of melting points of Al and Fe and the rapid formation of fragile intermetallic compounds (IM) make the welding of Al-based and Fe-based alloys at most very difficult if not impossible. Nonetheless, the need of such joints is growing since one tends to incorporate more and more aluminum parts as replacement of “low stressed” steel parts in order to achieve lightweight structures, especially in transportation industry. Here the idea is to depose a thick (<<mm) layer of aluminum on the steel using a powder additive manufacturing process: the cold spray. Aluminum powder is blown toward the steel using pressured gas at rather low temperature (around 80°C). The aluminum part is then welded to the additive manufactured aluminum layer on the steel using conventional laser welding. In the second part of this presentation copper deposition using cold spray is used on thin PCB conductors to allow laser welding of connectors.
Surface pre-treatment is fundamental in thermal spraying processes to obtain a sufficient bonding strength between substrate and coating. Different pre-treatments can be used, mostly grit-blasting for current industrial applications. This study is focused on Cu-Al2O3 coatings obtained by Low Pressure Cold Spray on AW5083 aluminum alloy substrate. Bonding strength is measured by tensile adhesion test, while deposition efficiency is measured. Substrates are textured by laser, using a pattern of equally spaced grooves with almost constant diameter and variations of depth. Results show that bonding strength is improved up to +81% compared to non-treated substrate, while deposition efficiency remains constant. The study of the samples after rupture reveals a modification of the failure mode, from mixed failure to cohesive failure. A modification of crack propagation is also noticed, the shape of laser textured grooves induces a deviation of cracks inside the coating instead of following the interface between the layers.
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