Effects of Impurity on Microstructure and Hardness in Pure Al Subjected to Dynamic Plastic Deformation at Cryogenic Temperature

Microstructure and hardness were investigated in pure AI samples with different purities (5N: 99.999%, 4N: 99.993%, and 2N: 99.7% in weight) subjected to dynamic plastic deformation at cryogenic temperatures. The saturated sizes of refined grains/subgrains in these samples induced by plastic deformation are about 240 nm without an obvious impurity effect, but the dislocation density in 2N AI is evidently higher than that in other samples. Boundary misorientations for 5N and 4N AI are below 10° with average values of 2–3°, while the average misorientation for 2N AI is obviously larger, being about 14°. Microhardness of LNT-DPD 2N AI is higher than that of 5N and 4N AI, owing to the enhanced dislocation density as their grain/subgrain sizes are almost identical.