Improving the Mechanical Properties of Mg–Gd–Y–Ag–Zr Alloy via Pre‑Strain and Two‑Stage Ageing

In this study,we investigated the effects of single-stage ageing(SSA),two-stage ageing(TSA),2%pre-strain+single-stage ageing(P2%SSA)and 2%pre-strain-I-two-stage ageing(P2%TSA)on the mechanical properties of as-extruded Mg-8Gd-3Y-0.5Ag-0.5Zr alloy(E alloy).Compared with the SSA treatment,the TSA treatment increased the number density of/β'phase.The P2%SSA and P2%TSA treatments generated theγ'phase and chain-like precipitates in addition to the/β'phase.The contributions of these ageing treatments to the alloy strengthening can be ranked as P2%TSA>P2%SSA>TSA>SSA,because the increments in the tensile yield strength were estimated to be 199 MPa>148 MPa>144 MPa>110 MPa.Dif­ferent from the traditional strengthening of/β'phase in the E+SSA and E+TSA alloys,the composite precipitates compris­ing the/β'phase,γ'phase and chain-like precipitates in the E+P2%SSA and E+P2%TSA alloys provided better combined strengthening effect.The/β'phase was still dominated in the strengthening effect of the composite precipitates.Owing to the higher number density of/β'phase in the composite precipitates,the E+P2%TSA alloy exhibited the better mechanical performance as compared with the E+P2%SSA alloy.Finally,the E+P2%TSA alloy had the ultimate tensile strength of 452 MPa,the tensile yield strength of 401 MPa and elongation to failure of 3.3%.