Microstructure and Hardness of Laser Shocked Ultra-fine-grained Aluminum

Ultra-fine-grained commercial purity aluminum was produced by severe cold rolling, annealing and then straining at ultra-high rate by a single pass laser shock. Resulted microstructure was investigated by transmission electron microscopy. Microhardness of annealed 0.6 pm ultra-fine grained aluminum increased by 67% from 24 to 40 HV. Many 0.3 pm sub-grains appeared at the shock wave center after a single pass laser shock, while high density dislocation networks were observed in some grains at the shock wave edges. Accordingly, microhardness at the impact center increased by 37.5% from 40 to 55 HV. From the impact center to the edge, microhardness decreased by 22% from 55 to 45 HV.