Behavior of Oxide at Diffusion-Bonded Interface of Al-Mg-Si Series 6063 Alloy

Diffusion-Bonding Mechanism of Aluminum Alloys by Transmission Electron Microscopy (Report 1)

Abstract

The behavior of the superficial oxide film during the diffusion bonding of Al-Mg-Si series 6063 alloy and its influence on the bond strength have been investigated mainly by TEM observations in order to explain the effect of alloying elements on the bondability of aluminum alloys. When faying surfaces were finished by electropolishing, crystalline oxide particles less than a few 10^-1μm in size were found to be dispersed on the joint interface of 6063 alloy, whereas rather continuous film of amorphous oxide remained at the joint interface of commercially pure aluminum. When faying surfaces were finished by wire brushing, an interfacial zone of a few μm thickness involving a number of fine oxide particles were found in the joint of 6063 alloy. A similar interfacial zone was also observed in the joint of pure aluminum, but its thickness and density of oxide particles were much greater than those in the joint of 6063 alloy. The crystalline oxide particle at the joint interface of 6063 alloy was identified as Al₂MgO₄ by SAD patterns. The formation of Al₂MgO₄ can be thermodynamically explained as a result of the following reaction between the superficial oxide film (Al₂O₃) and Mg : Mg+4/3 Al₂O₃→ Al₂MgO₄+2/3 Al. The tensile strength of the 6063 alloy joint was much higher than that of the pure aluminum, suggesting that the above difference in the behavior of the oxide film at the joint interface improved the bondability of 6063 alloy.