[en] The microstructures and tensile properties of extruded Mg-1Gd-0.5Zn-xCe sheets with various Ce contents (0, 0.3, 0.7 and 1.2 wt%) were investigated at room temperature. Ce addition refined the grain size and resulted in the formation of new Mg₁₂Ce phases. The volume fraction of Mg₁₂Ce phases increased with the increase of Ce additions, which impeded the growth of dynamic recrystallized grains during extrusion and consequently led to the texture weakening of Mg-1Gd-0.5Zn based sheets. Grain refinement and massive Mg₁₂Ce phases provided the highest strength in the Mg-1Gd-0.5Zn sheet with 1.2 wt% Ce addition. Moreover, due to more basal slip, pyramidal slip activity and uniform strain distribution, the ductility of extruded Mg-1Gd-0.5Zn sheet with 0.3 wt% Ce addition along the extrusion direction exhibited the maximum value of 33.6%, which was approximately 17.9% higher than that of the Mg-1Gd-0.5Zn sheet. However, with the further increase of Ce additions (0.7 and 1.2 wt%), the ductility of the sheets deteriorated gradually, which was associated with the increase of coarse Mg₁₂Ce particles.

[en] The bendability of Mg–Gd binary alloy at room temperature is significantly improved through the pre-compression and subsequent annealing (PCA) process. The results show that the formed angle of PCA sample (36°) is more excellent compared with the as-extruded (AE) sample (115°) during three-point bending test, which is mainly attributed to the variation of deformation mechanisms in the tension region. Basal slip dominates the tension strain in the extrados of AE sample, while {10–12} tension twinning and basal slip are activated simultaneously in the same region of PCA sample. The activation of {10–12} twins leads to higher Schmid factor (SF) for basal slip. It provides more prismatic slip activity in the twined areas, which enhance the coordination in thickness strain of PCA sample during the bending test. Therefore, the PCA process gives an insightful information for ameliorating bendability of Mg alloy.

[en] Highlights: • Extrusion dies with different angles (30°, 45°, 60°, and 90°) were adopted to produce AZ31 sheets. • Different effective strain could be introduced during extrusion due to the variation in die angles. • Large difference in effective strain along normal direction formed during sheet forming when using the 45° extrusion die. • The sheet processed by 45° extrusion die showed excellent room mechanical properties. Mg-3Al-1Zn (AZ31) alloy sheets fabricated using extrusion dies with angles of 30°, 45°, 60° and 90° were investigated. Finite element method was used to analyze the effective strain distribution in AZ31 Mg alloy during extrusion. The microstructure, texture and final mechanical properties were determined and compared among various extruded AZ31 sheets. Results demonstrated that the difference of effective strain was introduced during extrusion due to the variation in die angles. In the case of the 45° extrusion die, a large difference in effective strain along normal direction could form during sheet forming, which resulted in a uniform microstructure and weak basal texture of extruded AZ31 sheet. Therefore, the sheet processed using 45° extrusion die showed lower yield strength and r-value, but higher ductility and n-value. This study suggested that optimization of extrusion die angle could be an effective method to improve the mechanical properties of AZ31 Mg alloy sheets.

[en] Effects of Ca content (0.0, 0.5, 1.0, 2.0 wt%) on the microstructure, texture and mechanical properties of Mg-1.0Sn-0.5Zn-based alloys were investigated. The results stated that secondary phase of Mg-Sn-Zn alloy was transformed from Mg₂Sn to CaMgSn and Mg₂Ca with an increase in the Ca content. Ca addition also seriously affected the dynamic recrystallization and texture formation during the extrusion process. As for the as-extruded alloys, as Ca content increased from 0.0 to 2.0 wt%, the grain size was significantly decreased from ∼25 μm to 4–6 μm, whereas the texture type was converted from strong basal texture into weakened extrusion direction (ED)-split texture. Under tension, the elongation to fracture of the as-extruded Mg-Sn-Zn alloy was increased initially with the addition of Ca (0.0–1.0 wt%), and then decreased after 2.0 wt% Ca addition, whereas the counterpart in compression was changeless regardless of Ca content. Both tensile and compressive yield strengths of Mg-Sn-Zn alloy were monotonously increased with increasing Ca content, whereas this increment of yield strength induced by Ca addition was more pronounced in compression than that in tension. Obviously improved tension-compression yield asymmetry of Mg-Sn-Zn alloy via Ca addition was ascribed to grain refinement, texture modification and newly formed CaMgSn and Mg₂Ca phase precipitates.

[en] Highlights: • The grains of Mg-5Nd alloy were refined by addition of Al. • The mechanical properties of Al refined Mg-5Nd alloys were improved. • Crystallographic matching between Al₂Nd and α-Mg was calculated. The microstructures and mechanical properties of as-cast Mg-5Nd-xAl (x = 0, 0.8, 1.6, 2.4 and 3.0 wt%) were investigated by the optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and uniaxial tension test. The addition of 3.0 wt% Al led to the most significant grain refinement of Mg-5Nd alloy with the reduction of average grain size from 448 μm to 68 μm. The grain refinement was attributed to the formation of Al₂Nd particles as the Al₂Nd particles acted as effective grain refiners for the Mg matrix confirmed by XRD analysis, SEM observation, and crystallography calculation. The mechanical properties of as-cast Mg-5Nd alloy increased obviously after the addition of Al. The yield strength, ultimate tensile strength and elongation of the as-cast Mg-5Nd-3.0Al alloy were enhanced by about 45.3%, 72.4% and 264.0%, respectively, compared to as-cast Mg-5Nd alloy. The improvement of mechanical properties was mainly ascribed to the refined grains and secondary phase strengthening.

[en] This paper provided an effective plastic deformation technique, asymmetric porthole die extrusion, for fabricating AZ31 magnesium alloy sheets. Three kinds of asymmetric porthole extrusion dies were designed and entitled as APE-45, APE-60 and APE-90 die in terms of asymmetric porthole die angle, respectively. The effect of different APE processes on the microstructures, texture evolutions and mechanical properties of AZ31 sheets was investigated at room temperature. For comparison, conventional extrusion (CE) and symmetric porthole die extrusion (PE) were also conducted on processing AZ31 sheets. Shear deformation induced by APE declined the grain size and promoted a broad angular distribution of basal planes in the APE sheets compared with the CE and PE sheets. Especially, the APE-90 sheet obtained finest grain size of 5.2 µm and made basal planes tilted towards the extrusion direction by ~ 21° rotation in the sheet plane. With increasing asymmetric porthole die angle, the volume fraction of recrystallized grains gradually increased, resulting in the decrease of basal pole intensity. Due to the increased activity of basal slip, APE sheets exhibited the decrease in yield strength and r-value and increase in elongation to failure, especially for the APE-90 sheet. The improved formability of the APE sheets was attributed mainly to texture weakening. The APE-90 sheet exhibited the highest index Erichsen value and improved by ~ 74% and ~ 94% compared to the CE and PE sheets, respectively. Consequently, microstructure-texture control induced by APE could enhance the room-temperature stretch formability of AZ31 sheets.

[en] Effects of Al addition (0.0, 0.5, 3.0, 7.2 wt%) on microstructure, texture and mechanical properties of Mg-3.5Ca based alloys were investigated. Our results revealed that the addition of Al to the as-cast Mg-3.5Ca alloy resulted in the transformation of precipitated secondary phase from Mg₂Ca to (Mg, Al)₂Ca, Al₂Ca and even Mg₁₇Al₁₂ phase. Moreover, the as-cast microstructure evolution influenced dynamic recrystallization and texture formation in the subsequent extrusion process. As Al content increased from 0.0 to 7.2 wt%, the elongation to fracture (EL) of as-extruded Mg-3.5Ca alloy was monotonously increased from 1.9% to 9.8% in tension, while counterparts were changeless in compression. As-extruded Mg-3.5Ca-3.0Al alloy showed higher yield and ultimate strength increased by about 42.2 MPa and 71.4 MPa than those of extruded Mg-3.5Ca alloy in tension, respectively. Moreover, when Al addition was up to 7.2 wt%, both tensile yield strength and ultimate tensile strength were in steep decline. The effects of Al addition on compressive mechanical properties (compressive yield strength and ultimate compressive strength) were similar to that in tension. Especially, significantly deteriorated tension-compression asymmetry (TCA) of Mg-3.5Ca-7.2Al alloy was ascribed to grain coarsening and secondary phase transformation. Besides, Al addition also had a significant impact on the hardening capacity (Hc) and strain hardening behavior of Mg-3.5Ca alloy. In particular, as 7.2 wt% Al was added, the hardening capacity of the Mg-3.5Ca alloy was significantly increased from 0.09 to 0.56 in tension. As a result, proper Al addition to Mg-3.5Ca alloy could improve the comprehensive mechanical performance, whereas excessive Al addition not only significantly decreased the strength, but also deteriorated the TCA performance.

[en] In order to develop new magnesium alloy sheets with a good balance between ductility and stretch formability at room temperature, here we designed an Mg alloy with dilute Sn and Y and investigated the microstructure, texture, mechanical properties and stretch formability of Mg-0.4Sn-0.7Y in wt% (TW00) alloy compared with AZ31 alloy under extrusion and hot rolling-annealing conditions. We found that, after extrusion, the extruded TW00 (TW00-E) sheet exhibited a more homogeneous complete dynamic recrystallized microstructure and a splitting texture character with ~$\pm$20° tilted to the extrusion direction, compared with the extruded AZ31 (AZ31-E) sheet. After hot rolling-annealing at 400 °C, both the hot rolled annealed TW00 (TW00-RA-400) and AZ31 (AZ31-RA-400) sheets presented similar complete static recrystallized microstructures. However, significant texture weakening occurred in the TW00-RA-400 sheet rather than the AZ31-RA-400 sheet, due to static recrystallization induced by twins and grain boundaries. Tensile tests revealed that the TW00-E and TW00-RA-400 sheets with high Schmid factor (SF) for basal slip exhibited high ductility (~ 33% and ~ 32%). Simultaneously, prismatic slip and texture weakening played a significant role on decreasing r-values for the TW00-E and TW00-RA-400 sheets, respectively, which contributed to the improvement in stretch formability (~ 6.2 mm and ~ 5.4 mm) at room temperature. Therefore, we concluded that the TW00 alloy provided a bright prospect to achieve a good balance between the ductility and stretch formability at room temperature via extrusion or hot rolling-annealing.

[en] In this work, Mg-3Al-1Zn/Mg-0.3Y (AZ31/W0) laminated composite sheet was successfully fabricated by porthole die extrusion. Herein, microstructures, textures and stretch formability at room temperature of the AZ31 sheet, the W0 sheet and AZ31/W0 laminated composite sheet were systematically investigated and compared. The results showed that a tiny diffusion zone of ~ 0.35 µm and crystallographic interface were observed in the AZ31/W0 interface, indicating that the AZ31/W0 laminated composite sheet had a well bonding interface. The stretch formability at room temperature of the AZ31/W0 laminated composite sheet was apparently improved by ~ 71% and ~ 20%, respectively, as compared with the AZ31 sheet and W0 sheet. The activation of more basal slip in the W0 layer of the AZ31/W0 laminated composite sheet and the formation of extensive tensile twins in the AZ31 layer, which could effectively accommodate through-thickness strain during stretch forming, were assumed to be the main contribution to the stretch formability enhancement. Therefore, the bimetal laminated composite sheet provided a new thought to achieve high stretch formability Mg alloys via the porthole die extrusion.

[en] Here, Mg-0.4 wt%Sn based alloys containing different Y contents, Mg-0.4Sn-xY (x = 0, 0.7 and 2.0 wt%) alloys, were extruded into the sheets to systemically investigate the role of Y element on the microstructure, texture and mechanical properties of extruded Mg-0.4Sn alloy. We found that, with the Y addition, the average grain size gradually was reduced and the typical basal texture was transformed into the splitting one tilted to the extrusion direction. Moreover, the evidence of low number density and rough grain boundary cracks after tension indicated the strengthening in grain boundary cohesion with the Y addition. Besides more basal slips, the activation of prismatic slip and high intergranular strain propagation capacity were observed, which efficiently accommodated the sheet strain at room temperature. Those mentioned key factors contributed to the high room-temperature ductility of Mg-0.4Sn-0.7Y sheet. However, the formation and coarsening of Sn₃Y₅ and MgSnY phases were increasingly severe with increasing the Y addition to 2.0%. Those coarse secondary phases served as crack sources during tension deteriorating the ductility of Mg-0.4Sn-2.0Y sheet at room temperature. Therefore, we concluded that Y micro-alloying provided a new insight to achieve a superior room-temperature ductility of Mg-0.4Sn sheet.