This paper investigates the effect of liquation in the partially melted zone (PMZ) on the stress–strain behaviour of the AA7075 arc fusion welds. It is identified that the presence of micro-sized Cu-rich second phases in the initial microstructure of the AA7075 is responsible for constitutional liquation in the PMZ. Although the liquation cracking can be avoided using the proper selection of filler metal, it is demonstrated that the formation of brittle Al2Cu-type intermetallic-containing eutectic structure resulting from non-equilibrium solidification of the liquated grain boundaries can induce a severe loss of ductility in the PMZ. This calls for proper strategies to minimise the grain boundary liquid film thickness to produce a more reliable fusion weld on AA7075 alloy.
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