TWI

The fine scale precipitation in the nugget zone and in the HAZ of a weld in aluminium alloy AA-6082 (Al, 0.7%Mg, 0.5%Mn, 0.9%Si) of thickness 5-10 mm made by friction stir welding (FSW) was examined using transmission electron microscopy. The dissolution and persistence of different Mg-Si precipitates in the alloy were investigated in the two zones with a view to understanding the softening observed in friction stir welds. From literature data the peak temperature of the HAZ was estimated. By combining the information about the temperature distribution in the various zones with the observations of the precipitation, a better understanding of the microstructure, the hardness variation and, consequently, the location of fracture in transverse tensile test specimens, was obtained. The results are compared with published data from friction stir welded AA-7075 alloy.

1st International Symposium, 14-16 Jun 1999, Session 05: Microstructure & Corrosion 1, Paper 03