With the objective of clarifying the influence of materials plastic behaviour in friction stir weldability, two base materials, a non-heat-treatable (AA 5083-H111) and a heat-treatable aluminium (AA 6082-T6) alloy, characterized by markedly different strengthening mechanisms and microstructural evolution at increasing temperatures, which conduct to markedly different viscoplastic behaviour, were compared. The plastic properties of the base materials, under different testing conditions, which include tensile testing at different temperatures and strain rates, were analysed and compared. The two base materials were also welded under varied welding conditions, using different FSW tools and welding parameters, in order to characterize its weldability in FSW. An important relation between material flow during friction stir welding and the plastic behaviour of the base materials, at different temperatures and strain rates, was found. The obtained results also show that materials plastic properties also influence the contact conditions at the shoulder-base material interface.
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