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In this work, the Mg97Y2Zn (at%) alloys have been processed by the rotary-die (RD) ECAP technique under different temperature or pass conditions to tailor the microstructure and mechanical properties. The results reveal that the DRX ratio (VDRX) increases with the increase of ECAP pass or temperature, weakening the texture intensity. The refinement of DRXed grains saturates after 9 passes of ECAP at 350 °C, while the size of DRXed grains (dDRX) monotonically decreases with the reduction of temperature from 400 °C to 300 °C in the case of the same pass number (9P). The combination of fine dDRX, large VDRX, and directionally arranged LPSO phases along the extrusion direction endows the 350 °C–9P alloy with the optimum strength and ductility synergy, exhibiting the tensile yield strength (TYS) of 267 MPa, ultimate tensile strength (UTS) of 318 MPa, and elongation of 10.3%. However, the larger VDRX, weaker texture, less low-angle grain boundaries combine to improve the elongation (14.7%) of the 400 °C–9P alloy at the expense of the TYS (231 MPa) and UTS (303 MPa). This paper provides useful information to optimize the RD-ECAP parameters for the fabrication of high-performance Mg97Y2Zn alloys.

The hot deformation behavior of AZ42 alloy was observed using thermal compression tests at a temperature scope of 250–400 °C and strain rate scope of 0.001–1 s−1. True stress-strain curves exhibited a combination of work hardening and dynamic softening features. A Northern Goshawk algorithm (NGO)-optimized artificial neural network (ANN) model was proposed. The established NGO-ANN model demonstrated impressive prediction accuracy, achieving a high determination coefficient of 0.991, a mean absolute percentage error of 3.51 %, and a root mean square error of 2.73. Subsequently, three-dimensional (3D) hot processing map based on the dynamic material model (DMM) theory was created. There were three different regions within the processing maps: the flow instability region (region A: 250–260 °C, 0.02–1 s−1, and region B: 300–400 °C, 0.01–0.1 s−1), high-power dissipation coefficient region (region C: 350–400 °C, 0.001–0.02 s−1, and region D: 300–350 °C, 0.5–1 s−1), and low power dissipation efficiency safety region (region E: the rest ones). Microstructural analysis revealed significant local plastic flow features in the flow instability region and a combination of coarse initial deformation grains and fine dynamic recrystallization (DRX) grains in the low power dissipation efficiency safety region. Fine and uniform grains were observed in the high-power dissipation efficiency region with DRX degree VDRX as high as 85.6 %, resulting in the best mechanical properties. Based on the established 3D hot processing map, the optimal process domains were determined.

In this work, Mg98.5Zn0.5RE1 (RE = Gd and/or Y) and Mg97Zn1Y2 (at%) alloys were subjected to homogenization and equal channel angular pressing (ECAP) to systematically compare the microstructure evolution and mechanical properties. The results indicate that, instead of the lamellar LPSO phases in the as-cast Mg-Zn-Y series alloys, the β-Mg5(Gd, Zn) phases appear in the as-cast Mg98.5Zn0.5Gd1 alloy which tend to be dissolved during homogenization. The furnace cooling after homogenization promotes the precipitation of numerous lamellar LPSO phases in all the studied alloys which inhibit the DRX behavior but facilitate the operation of kinking deformation during ECAP for the Mg98.5Zn0.5RE1 alloys, especially the Mg98.5Zn0.5Gd1 one. After the 5p-ECAP process at 350 °C, the larger density of kink bands, more LAGBs (low-angle grain boundaries) and lower SFB (Schmid factor for basal slip) combine to endow the Mg98.5Zn0.5Gd1 alloy with the higher strength-ductility synergy, exhibiting the tensile yield strength (TYS) of 214 MPa and elongation of 9.6%. The Mg97Zn1Y2 alloy with the larger volume fraction of interdendritic LPSO phases and dynamically recrystallized (DRXed) regions exhibits the superior ultimate tensile strength (UTS) of 277 MPa and moderate elongation of 7.2%.

Quantifying damage to improve the constitutive models that better account for damage prediction is of great importance in metal forming process. In this study, high-resolution micro-focus X-ray Computed tomography (CT) system, together with loading-unloading tensile test, were employed to quantify the 3D interactions of micro-voids evolution in the biocompatible alloy stainless steel 316L (SS316L). The specimen material was tensile deformed and interrupted at several strain intervals prior to failure, X-ray CT was then performed to quantify the damage evolution via the detected changing in size, number, distribution, and volume fraction of micro-voids (VFMV) after each specified strain increment. Thereby the nature of ductile damage, which involved the dynamic evolution mechanism of the nucleation, growth and coalescence of micro-voids, was revealed. Furthermore, an improved micromechanics-based damage (micro-damage) model considering large deformation condition was implemented into finite element (FE) package ABAQUS for the damage prediction. The damage of the specimen under tensile deformation with a wide range of stress states was predicted and a good agreement with experimental data was achieved in terms of damage distribution and evolution. It is concluded that the findings of this study not only reveal the dynamic evolution mechanism of the micro-voids in the damage process intuitively from the experimental point of view, but also provide more accurate material parameters for the theoretical damage modelling, so as to obtain more convincible damage prediction results in the metal forming process.

Abstracts: This study aims to explore the effect of Zn content on mechanical properties and degradation behaviour of biodegradable Mg–Y–Zn (WZ) alloys via mechanical and in-vitro testing. Microstructure characterization showed that the morphology and composition of the secondary phases changed significantly with the increase of Zn content. The continuous precipitation of long-period stacking ordered (LPSO) phase led to an increase in the strength of the WZ alloys. However, the corrosion resistance of the WZ alloys increased initially and then decreased as Zn content increased. In the Mg-9.1Y-1.8Zn (WZ92) alloy, the continuous rod-like LPSO phases formed an effective degradation barrier to prevent the corrosion penetration, thus leading to a uniform and slow degradation process. Discontinuous and dispersed (i.e., lamellar-like) LPSO phase existed in the Mg-9.2Y-3.1Zn (WZ93) alloy cannot act as the degradation barrier, and the intragranular fine lamellar structure would aggravate corrosion and promote corrosion penetration into the α-Mg matrix. In addition, the WZ93 alloy with high content of LPSO phase formed more micro-galvanic couples, which exacerbated the micro-galvanic corrosion. EIS results revealed that the WZ92 alloy exhibited better corrosion resistance due to the formation of a more stable and thicker surface film. This study demonstrates that the Mg–Y–Zn alloy with tunable mechanical and degradation properties can be fabricated efficiently and economically by regulating the Zn content, and is expected to be a promising candidate in the field of degradable medical implant.