Microstructural and mechanical characterization of a friction stir welded Al-alloy

The microstructure and mechanical properties of a friction stir welded 6013 aluminum alloy have been investigated. A combination of optical and transmission electron microscopy was used to characterize the microstructure of the weld, the heat affected zone and the base material. Friction stir welding causes dynamic recrystallization in the weld resulting in smaller and equiaxed grains as compared to the larger elongated grains of the base material. The grain size of the heat-affected zone is retained. The strengthening precipitates in the weld are dissolved while those in the heat affected zone coarsened considerably. Mechanical properties were characterized using microhardness measurements and tensile tests. Microhardness profiles show that the heat-affected zone is the softest region. Tensile tests transverse to the weld revealed that the strength of the weld is reduced and that fracture takes place in the heat affected zone.