Root-mean-square (RMS) stress peak of acoustic emission is formed under mechanical loading (55 MPa) of alloy at temperatures from 100 0C up to 350 0C. Further loading causes the RMS stress peak to be observed only in cycles with loading increased relative to previous cycles (for example, up to 65 MPa) and without strain growth in cycles. Increasing stress leads to increasing of internal energy parameter of acoustic emission J, which indicates increasing of diffusion mobility of magnesium atoms in the alloy. That results in a partial breakdown of supersaturated solid solution with diffusion mechanism occurred under mechanical activation. Plastic deformation proceeds at temperatures above 400 0C and mechanical stress above 50 MPa due to activation of grain-boundary processes with predominant grain boundary sliding. An increasing of RMS stress amplitude demonstrates an increasing of intensity of dislocation generation under grain-boundary processes forming bands of deformation.