Abstract
Repetitive upsetting extrusion (RUE) was applied to the as-homogenized Mg-12.0Gd-4.5Y-2Zn-0.4Zr (wt %) alloy at 773 K. The microstructure evolution of the alloy during RUE was investigated. The results indicated that almost all Mg5(Gd,Y,Zn) phases and fine-lamellar long-period stacking-ordered (LPSO) phases were dissolved into the matrix after homogenization treatment at 793 K for 16 h. After one RUE pass, dynamic recrystallization (DRX) occurred. During subsequent RUE passes (from one to three passes), average volume fractions of DRXed grains increased from 43.9% to 65.8%, and that of fine-lamellar and block-shaped LPSO phases gradually decreased. All samples exhibited a typical bimodal microstructure consisting of some initial grains containing fine-lamellar LPSO phases, but consisting mostly of fine-DRXed grains with a mean grain size of 6 μm. Because of an increase in the accumulated strains, the coarse grains were substituted with fine-DRXed grains, the grains were gradually refined, and the microstructure distribution became more homogeneous.
Highlights
Mg and its alloys have attracted extensive attention in recent years as the most promising lightweight component materials
The distributed along grain boundaries, with a mean grain size of about μm
Three different phases distributed along grain boundaries, with a mean grain size of about 70 μm
Summary
Mg and its alloys have attracted extensive attention in recent years as the most promising lightweight component materials This is due to their superior mechanical properties, low density, good creep resistance, and excellent damping capacity. Its superior mechanical properties were attributed to ultrafine hcp-Mg grains ranging in size from 100 to 200 nm and to the fine-lamellar LPSO phase. This indicates that improving microstructures can result in an alloy with excellent performance. Increasing strains during severe plastic deformation (SPD) can lead to the original grains being completely substituted with grains that have undergone dynamic recrystallization (DRX) [11]. SPD, and the evolution of isothermal RUE on the microstructure of Mg-12.0Gd-4.5Y-2.0Zn-0.4Zr alloy was investigated.
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