Behaviour of oxide at diffusion‐bonded interfaces in Al‐Mg‐Si series 6063 alloy: Study of diffusion‐bonding mechanism of aluminium alloys by transmission electron microscopy (1st Report)

Summary

The behaviour of the surface 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 aluminium alloys. When faying surfaces were finished by electro‐polishing, crystalline oxide particles smaller than a few 10^‐1 μm in size were found to be dispersed on the joint interface of 6063 alloy, whereas a rather continuous film of amorphous oxide remained at the joint interface of commercially pure aluminium. When faying surfaces were finished by wire‐brushing, an interfacial zone of a few μ m thickness involving a number of fine oxide particles was found in the joint in 6063 alloy. A similar interfacial zone was also observed in a joint in pure aluminium, but its thickness and the density of oxide particles were much greater than those in the joint in 6063 alloy. The crystalline oxide particles at the joint interface of 6063 alloy were 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 (A1₂O₃) and Mg: Mg + 4/3 Al₂O₃?Al₂MgO₄ + 2/3 Al. The tensile strength of the 6036 alloy joint was much higher than that of the pure aluminium, suggesting that the above difference in the behaviour of the oxide film at the joint interface improved the bondability of 6063 alloy.