Cold butt welding of dissimilar aluminum alloys: Characterization and interface bonding conditions

Cold Butt Welding (CBW) exploits plastic deformation to enable room temperature fabrication of joints with comparable strength to their base metals. Challenges arise when CBW involves alloys with very different mechanical properties, where the necessary conditions to reach their plastic regime differ significantly. The present study unravels the conditions at the interface under which dissimilar AA1070 and AA6082 aluminum wires achieve bonding. Statistical studies were performed to establish a minimum deformation threshold required for successful bonding. The joints were characterized through optical light microscopy, scanning electron microscopy, and micro and nano hardness examinations. In-situ tensile testing was conducted to evaluate the bond strength and failure mechanism. It was found that during the CBW process, at increasing force, the constraints generated by the clamping apparatus on the wires are such that the soft alloy can exceed its ultimate strength and eventually reach the yielding stress of the hard alloy at the interface, allowing both materials to plastically deform and bonding to occur. Moreover, the deflection in the flow of both materials leads to grain refinement and crystalline reorientation inside a region centred around the bonded interface. The severely deformed area was proven by hardness and tensile testing to be the strongest part of the weld, typically identified as the mechanically affected zone.