Achieving ultra-high strength in Mg–Gd–Ag–Zr wrought alloy via bimodal-grained structure and enhanced precipitation

Yu Zhang^1,2，Wei Rong²，Yujuan Wu²，Liming Peng²

1. College of Materials Science and Engineering, Chongqing University2. National Engineering Research Centre of Light Alloy Net Forming and State Key Laboratory of Metal Matrix Composite, School of Materials Science and Engineering, Shanghai Jiao Tong University

摘 要：Mg–13.1 Gd–1.6 Ag–0.4 Zr（wt%） alloy was either iso-thermally extruded at 350?C or differentialthermally extruded with respectively pre-heated billet at 500?C and die at 350?C. The iso-thermal extrusion leads to a near fully recrystallized structure and a [0001]//ED（extrusion direction） texture.In contrast, the differential-thermally extruded alloy develops a bimodal-grained structure composed of fine equiaxed recrystallized grains and coarse elongated unrecrystallized grains with a0110//ED texture. The differential-thermally extruded alloy has a higher number density of precipitates after postextrusion ageing than that of the iso-thermally extruded counterpart. Moreover, precipitation in the differential-thermally extruded alloy is further enhanced with cold rolling before ageing. Finally, the alloy obtains room temperature tensile yield strength of 421 MPa and ultimate tensile strength of 515 MPa via differential-thermal extrusion, cold rolling and ageing, mainly ascribed to the coupled strengthening from the bimodal-grained structure and enhanced precipitation. Strength of the alloy is noticeably higher than those of Mg–Gd（–Y）–Ag extruded alloys with similar compositions reported previously and is comparable to those of other high-strength Mg wrought alloys. The findings suggest that differentialthermal extrusion plus strain ageing is a suitable approach for achieving high strength in age-hardenable Mg alloys.

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