Constitutional liquation occurred at the friction interface of Al/Mg joints produced by continuous drive friction welding. This paper investigated the relationship between constitutional liquation and microstructure morphology of Al/Mg joints. The intermetallic compound γ-Al12Mg17 underwent morphological transitions from submicron-size particles to island-like lamellae, then to network structure as the Al content increased. The submicron-size γ-Al12Mg17 particles precipitated along the grain boundaries of α-Mg solid solution. The Mg–Al12Mg17 divorced eutectic structure was formed. The formation mechanism of eutectic structure was studied with Al–Mg binary phase diagram and Al–Mg–Zn ternary phase diagram. The network structure was derived from dendritic structure γ-Al12Mg17. Friction pressure could improve the liquid–solid hybrid microstructure morphology at the welding interface.
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