Flow patterns in friction stir welds of AA5083 and AA6082 alloys

•The pull of materials across the weld centre line is predominantly from the advancing side.•Mixture of materials only occurred in four regions of the weld.•The finest grain sizes were observed at the top side of the retreating side.•Fragmented grains with high dislocation density and density of Mg2Si phases affected the microhardness.

The flow patterns in dissimilar friction stir welds of AA5083-O and AA6082-T6 alloys have been studied. It was observed that material flows (pushes but does not mix) more from the advancing side into the retreating side. Material flow from the retreating side to the advancing side only occurs in the tool shoulder domain, and the pull is greatest at the transition region between the tool shoulder domain and the tool pin domain. It was also observed that materials tend to extrude out only in the thermomechanically affected zone of the retreating side, which was influenced by rotation of both the tool shoulder and the tool pin. The finest grains were present in the regions closest to the tool edge in the retreating side. The volume fraction of recrystallized grains increases down into the deeper part of the nugget from the flow arm region. Microhardness measurements revealed that regions of lowest hardness values were the nugget and the heat affected zone of the AA6082-T6 alloy side. The welding speeds had no influence on the microhardness values per se, but affected the mixing proportions in the flow arm and in the nugget stem.

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