Phase Transformation under the Influence of the Plastic Deformation in Al-22 at.% Zn Alloy in the Presence of Cu-additions

The plastic deformation effect on the phase transformation (grain boundary diffusion) for Al-22at.%Zn polycrystals in the presence of copper additions have been investigated in the range of aging temperature 303-513K under the solvus line of the alloy (557K). The copper additions are 1, 1.5 and 2 at.% of the alloy. Also, the degrees of plastic deformation involved by rolling are 5, 10,15 and 20%, respectively. The occurrence of the discontinuous precipitation reaction has been effective by the degree of plastic deformation and the addition of copper. The phase constituents involve the FCC Al-rich, HCP Zn-rich, and CuZn4 phases. The cell growth rate of discontinuous precipitation reaction of Al-Zn-Cu alloy is affected by the copper addition. The growth rates are higher by one order of magnitude than the value at the lowest aging temperature (303K). This is compared to the growth rate at zero plastic deformation. The experimental measurements of nucleation and the growth of the discontinuous precipitation with cold rolling occur. The grain boundary diffusivities determined are in good agreement with the radiotracer measurement data in the Al-Zn systems. While the values of the activation energy, Qo, of the discontinuous precipitation reactions are -35.94, -39.71 and -45.36KJ/mol. The values of the pre-exponential factors, (SDb)o, are 2.962*10-12, 3.21*10-12 and 6.53*10-12 m3/sec with cold rolling of 5,10, 15 and 20 percent, respectively.