Effect of Gd Content on the Microstructure and Mechanical Properties of Hot Extruded Mg-xGd-4Y-1Sm-0.5Zr Alloys

TL;DR

This study examines how varying Gd content affects the microstructure and mechanical properties of magnesium alloys, finding that higher Gd improves strength but reduces elongation.

Contribution

The novel contribution is the systematic investigation of Gd content's effect on microstructure evolution and mechanical behavior in hot-extruded Mg-Gd-Y-Sm-Zr alloys.

Findings

Increasing Gd content reduces non-dynamic recrystallized grain fraction from 46.3% to 9.3%.

Higher Gd increases β′ phase density and improves yield and tensile strength but lowers elongation.

Crack deflection and plasticity are observed in peak-aged alloys with no microcracks up to 6.6% strain.

Abstract

In this paper, the microstructure, mechanical properties, and strengthening mechanisms of hot-extruded Mg-xGd-4Y-1Sm-0.5Zr (x = 4, 7, 10, wt.%) alloys were studied. The results show that the hot extruded alloys exhibit bimodal grain structures, and with Gd content increasing, the fraction of non-dynamic recrystallized grains gradually decreases, with 46.3%, 38.6%, and 9.3%. After aging for 200 °C × 96 h, all three hot-extruded alloys reach peak-aged hardness, and as Gd content increases, the area number density of the β′ phase increases with Gd increasing, being 7.1 × 1015/m2, 9.9 × 1015/m2, and 16.5 × 1015/m2, respectively. And the yield strength (YS) increases from 287 MPa to 345 MPa, the ultimate tensile strength (UTS) increases from 365 MPa to 418 MPa, and elongation (EL) decreases from 8.5% to 4.2%. The tensile failure mechanism is quasi-cleavage fracture. With Gd content increasing, the dimples and tear ridges on fracture surfaces gradually decrease while cleavage facets increase. The peak-aged GWS741 alloy demonstrates optimal comprehensive mechanical properties, with YS, UTS, and EL reaching 332 MPa, 409 MPa, and 7.8%, respectively. During in situ tensile testing, coarse un-DRXed grains undergo prismatic ({101-0}〈112-0〉) slip, while DRXed grains experience basal (0001〈112-0〉) slip and twinning deformation. Even at 6.6% strain, no microcracks are observed, indicating excellent plasticity. During the tensile failure process, the main crack propagates along tortuous paths, showing crack deflection characteristics, where it either penetrates through elongated deformed grains or bypasses un-DRXed grains.

Figures