A study on the hardness and elastic modulus of friction stir welded aluminum alloy thick plate joints using micro-indentation

Micro-indentation technique was employed to study the hardness and elastic modulus for different positions along the thickness of weld nugget zone (WNZ) in friction stir welded aluminum alloy thick plate joints and base material (BM). Experimental results showed that maximum hardness and elastic modulus 2.11 and 81.6 GPa were obtained in the top of WNZ, minimum values 0.79 and 74.9 GPa present in the BM, respectively. For different positions, both of them were as follows: BM < bottom < middle < top. Meanwhile, the hardness decreased with the increase in grain size or the load. The rod-like shape precipitates presented in the BM and the round particles of top was smaller than that of middle and bottom, and the top of WNZ presents the higher dislocation density.