Abstract: In order to investigate the influence mechanism of the solution treatment on microstructure and impact behaviour of Mg-Gd-Y-Zr alloy, the microstructure of the alloy under different single-stage and two-stage solid solution processes was studied by means of optical microscope(OM), SEM and EDS, and the dynamic impact mechanics of the alloy under optimum single-stage and two-stage solution treatment were tested by using a split Hopkinson press bar(SHPB). The results show that the optimum single-stage solution treatment of the alloy is at 520 ℃ for 6 h, and the optimum two-stage solution treatment is at 350 ℃ for 6 h then at 520 ℃ for 1 h. Compared with single-stage solution treatment, the grain size of the alloy after double-stage solution treatment is significantly reduced, the RE-rich square particle phase composition changes, the Y content increases significantly and the Gd and Y contents are close to each other. The maximum compressive strength of the alloy after the optimum single-stage solution treatment is 503 MPa at a strain rate of 3649 s^-1, and the coordinated action of the dynamic precipitated particles and square-shaped RE-rich particles is an important factor in maintaining its excellent impact resistance. The maximum compressive strength of the alloy after the optimum two-stage solution treatment is up to 534 MPa at a strain rate of 4056 s^-1, which is significantly higher than that after the single-stage solution treatment mainly due to the reduced grain size and the synergistic effect of the RE-rich particles and dynamic precipitation particles.

Key words: solution process, Mg-7.5Gd-3Y-0.5Zr alloy, grain size, enriched rare-earth particles, dynamic mechanical properties