Influence of welding parameters and tool pin profile on microstructure and mechanical properties along the thickness in a friction stir welded aluminum alloy

Microstructure, second-phase particles and mechanical properties of the joint along the thickness of plate during friction stir welded 2219 aluminum alloy thick plate using different shapes pin were investigated in this paper. The top presented larger equiaxed recrystallized grain structure and finer second-phase particles compared to the middle and bottom. Thermo-mechanically affected zone and boundary were more optically distinct on the advancing side in comparison with the retreating side. Grain size and particles were much finer and dispersed using the first tool with three spiral flute or at the lower rotational speed of 300 rpm. The strength and ductility in top slices was slightly higher than that in middle and bottom, increased with increasing traverse speed from 60 to 100 mm/min or the decrease of rotational speed from 500 to 300 rpm using the first tool. The mechanical properties using the second tool was lower than that of first tool, which was consistent with the hardness curves.

► Different grain size and particles through the thickness presented.
► Thermal–mechanical affect zone and boundary were different on AS and RS.
► Strength and ductility of slices were different using different shapes pin.