Microstructure evolution and mechanical properties of Mg-Gd-Y-Ag-Zr alloy fabricated by multidirectional forging and ageing treatment

Mg-8.0Gd-3.7Y-0.3Ag-0.4Zr (wt%) bulk sample with exceptional high strength is successfully fabricated by multidirectional forging (MDF) and subsequent ageing treatment. The microstructure evolution and mechanical properties are investigated in this study. Results show that grain refining process during MDF is closely related to the dynamic recrystallization (DRX) behavior and a microstructure consisting of ultra-fine grains (similar to 0.8 mu m) and dynamic precipitates of Mg-5(GdY) is obtained when forged by 15 passes (Sigma epsilon = 4.5). After peak-ageing treatment, densely distributed beta' phase precipitates out from the matrix. Ag is mainly segregated in the dynamic precipitates. The forging-T5 sample (15 passes) exhibits a room mechanical property of 391 MPa in YS, 448 MPa in UTS and 3.9% in elongation to failure. The strength, retains 339 MPa in YS and 411 MPa in UTS when tested at 200 degrees C. The remarkable mechanical performance can be ascribed to the intensive grain refinement by MDF process, dynamic precipitates as well as precipitate strengthening by beta' phase.