Effect of tool rotating rate and subsequent artificial aging on microstructure and mechanical properties of 7050-T7451 alloy

Abstract

In this work, the effects of friction stir processing tool rotating rate and subsequent artificial aging on the microstructure and mechanical properties of 7050-T7451 alloy were investigated. The results show that the grain morphology and the evolution of precipitated phases were significantly affected by rotating rate and artificial aging treatment. Ultrafine equiaxed grains formed after FSP and the grain size tended to grow with the increase of rotating rate, however the growth rate decreased gradually. Nano-sized η' phases mainly dissolved back, accompanied by partial phases transformation at low rotating rate condition. With the rotating rate increased, η' phases were more fully dissolved and parts of η phases start to dissolve gradually too. The matrix supersaturation increased as the dissolution of η' & η phases, resulting improvement of the mechanical properties of the alloy via solid solution strengthening. Subsequent artificial aging treatment promoted the decomposition of solid solution, new GP zones and η' phases re-precipitated, and the density of precipitated phases were proportional to the degree of matrix supersaturation. And, the properties of the alloy were further improved by the precipitation strengthening effect of these new reprecipitated phase. • The grow rate of ultrafine equiaxed grains of FSPed 7050-T7451 alloy tend to decline with the increasing of FSP tool rotating rate. • The redissolution of nano-scale precipitates turn to be dominant in high FSP tool rotating rate. • New nano-scale precipitates re-precipitated during artificial aging resulting significant increasement of mechanical properties.