Dynamic nano precipitation behavior of as-cast Mg-4Li-4Zn-Y alloy during high temperature deformation

Dynamic nano precipitation behavior of as-cast Mg-4Li-4Zn-Y alloy during high temperature compression at 450 ℃ was investigated in this paper. The grains were coarse, interdendritic W-Mg3Y2Zn3 mainly existed at grain boundaries and MgZn2 mainly existed in grains in the as-cast alloy. After hot deformation at 400 ℃/0.1 s−1 and 450 ℃/0.1 s−1, complete dynamic recrystallization occurred, MgZn2 was dissolved and Mg24Y5 appeared. Compared with 400 ℃, the number of second phases was more and grains were finer at 450 ℃. Bulk W-Mg3Y2Zn3 particles were broken and partly dissolved during hot deformation, and Zn and Y atoms diffused from grain boundaries into inner grains. Diffused atoms were aggregated at defects caused by deformation, then nano precipitates with a size of tens of nanometers formed at these places without growth. High-density ultrafine nano precipitates with a size of several nanometers were also found. Grains were refined due to PSN progress promoted by relatively large particles and growth restraint by nano precipitates at grain boundaries. The combined strengthening effect of particle dispersion and grain refinement can significantly improve the mechanical properties. Texture in the alloy was randomized during high temperature deformation as well, which was beneficial to reduce mechanical property anisotropy.