Characterisation of microstructure and texture in friction stir welded joints of 5754 and 5182 aluminium alloy sheets

The microstructure and texture of friction stir welded joints of hot mill stock 5754 and 5182 aluminium alloy sheets were examined after a commercial joining process. The as received sheet was cut into two pieces, one piece was cold rolled with 20% reduction in thickness, whereas the other was subsequently aged at 230 degreesC for 100 h after the 20% prestrain. These two pieces with different thermal pretreatments were joined by friction stir welding (FSW). On FSW, a uniform fine grained microstructure in the through thickness of the sheet having a width corresponding to the diameter of tool shoulder was observed in both the 5754 and 5182 joints. Moreover, the microhardness profile did not reveal a softened heat affected zone between the weld and the base metal. An X-ray pole figure study showed that the 5754 and 5182 weld zones were not highly textured and both comprised of similar texture components. The calculated average sheet formability of the weld zones predicts a more isotropic behaviour than that for the start materials. Orientation image mapping of the weld zone in 5182 and semi-automatic electron backscatter pattern linescan analysis of the 5754 weld zone showed that most of the grain boundaries were high angle ones. This determination affirms that the weld zones in AA 5754 and AA 5182 joints undergo homogeneous dynamic recrystallisation throughout the thickness resulting in uniform mechanical properties.