EFFECT OF HEAT TREATMENT ON NANOSTRUCTURING IN HIGH-STRENGTH ALUMINUM ALLOY BY SEVERE PLASTIC DEFORMATION

Effect of prior heat treatment on nanostructuring of high-strength 7475 Al alloy, sub- jected to high-pressure torsion (HPT) at ambient temperature up to strain of ~7, was investi- gated. The alloy was (i) solution treated and water quenched, and then (ii) artificially aged before HPT. In distinction with the state (i), the state (ii) was characterized by the presence of nanoprecipitates of strengthening n - phase in Al matrix. It was shown that the initial alloy state significantly affected the morphology and parameters of nanocrystalline structures evolved. Mixed (sub)grain/cellular structure composed by both equiaxed and elongated crystallites, predomi- nantly separated by dislocation boundaries, was developed in the aged state, whereas more equiaxed and coarse crystalline structure with more equilibrium boundaries formed in the as- quenched material. It was concluded that high density precipitates in the alloy can delay the formation of nanograins in the deformation structures due to inhibition of dynamic recovery and homogenization of the dislocation slip.