Nanoindentation applied to an optimized FSW-AZ31 butt joint

Friction stir welding (FSW) technique was used to weld AZ31B-H24 alloy plates. The effect of the welding parameters, probe traverse velocity and probe revolution rate, on the butt joint quality was investigated. A sound FSW AZ31 butt joint was produced with a revolution rate to probe traverse ratio ?/? of 100 rev mm?1. Equiaxed grains were observed at the weld nugget zone and in the base metal. Larger grains were detected in the nugget compared to the base metal. Hardness measurements were performed using nanoindentation techniques. Nanohardness was compared to the more conventional microhardness measurements both performed along the mid-thickness of the cross section and along upper and lower surfaces. Nanohardness at the weld nugget zone was quite similar to that of the base metal, while a significant peak was detected at the TMAZ/HAZ interface. This peak was higher at the advancing side of the FSW joint than the one observed at the retreating side.