On the High Formability of AZ31-0.5Ca Magnesium Alloy

Improving the Mechanical Properties of Mg-5Al-2Ca-1Mn-0.5Zn Alloy through Rotary Swaging

To meet the demand for more extensive applications of Mg alloys, a Mg-5Al-2Ca-1Mn-0.5Zn alloy without RE was prepared in this paper, and its mechanical properties were further improved by conventional hot extrusion and subsequent rotary swaging. The results show that the hardness of the alloy decreases along the radial central region after rotary swaging. The strength and hardness of the central area are lower, but the ductility is higher. The yield strength and ultimate tensile strength of the alloy in the peripheral area after rotary swaging reach 352 MPa and 386 MPa, respectively, while the elongation remains at 9.6%, exhibiting better strength-ductility synergy. The grain refinement and dislocation increase caused by rotary swaging promoted strength improvement. The activation of non-basal slips during rotary swaging is an important reason for the alloy to maintain good plasticity while improving strength.

Effect of Rolling Parameters on Room-Temperature Stretch Formability of Mg-2Zn-0.5Ca Alloy

In this work, Mg−2Zn−0.5Ca (wt.%) alloy sheets fabricated according to various rolling parameters were evaluated to investigate the effect of rolling parameters on room-temperature stretch formability. The sheet rolled at 360 °C with a pass rolling reduction of 10~33% exhibited the worst I.E. value of 4.4 mm, while the sheet rolled at 360 °C with a pass rolling reduction of 20~50% exhibited the best index Erichsen (I.E.) value of 5.9 mm. Among the sheets, the (0002) basal texture intensity was the weakest, and the grain basal poles split away from the normal direction toward both the rolling direction and the transverse direction. Microstructural and deformation mechanism measurements of stretch forming to 2 mm for the sheet rolled at 360 °C with a pass rolling reduction of 20~50% by electron backscatter diffraction and in-grain misorientation axes showed that there was a higher activity of {10−12} extension twins and that a prismatic <a> slip was initiated. As a result, the weakening of the texture and the broader distribution of basal poles in the plane contributed to the improved formability of the sheet rolled at 360 °C with a pass rolling reduction of 20~50%.

Effects of Zn Addition on the Microstructure and Mechanical Properties of As-Extruded Mg-2Al-0.5Ca Alloy

The effects of Zn addition on the microstructure and tensile properties of as-extruded Mg-2Al-0.5Ca-xZn (x = 0, 0.3, 0.6, 0.9 wt.%) alloys were investigated in this work. The results showed that the extruded sheets exhibited a completely dynamically recrystallized microstructure, the grain size was refined, and texture weakening was achieved with Zn addition because of the segregation of Zn atoms on grain boundaries, which suppresses the growth of dynamic recrystallized grains. The addition of 0.6 wt.% Zn improved both the tensile strength and ductility of the as-extruded Mg-2Al-0.5Ca alloy. The as-extruded Mg-2Al-0.5Ca-0.6Zn alloy showed a 0.2% proof stress of 145 MPa, an ultimate tensile strength of 317 MPa, and an elongation of 30.0% along the extruded direction. The simultaneous improvement of strength and ductility was mainly due to the fine and homogeneous grain microstructure and the weakened extrude direction (ED)-tilted texture. The as-extruded Mg-2Al-0.5Ca-0.6Zn alloy showed little in-plane anisotropic tensile properties, with a 0.2% proof stress, ultimate tensile strength, and elongation in the 45° direction of 148 MPa, 299 MPa, and 25.0%, and those in the transverse direction of 148 MPa, 269 MPa, and 16.8%, respectively.

Microstructural Study of a Mg-Zn-Zr Alloy Hot Compressed at a High Strain Rate

Understanding the correlation of plasticity with deformation and dynamic recrystallization (DRX) behaviors, in magnesium (Mg) alloys deformed under high-strain-rate conditions, is increasingly important for wrought Mg processing. In the present study, a ZK30 (Mg-2.61%Zn-0.66%Zr by weight percent (wt.%)) alloy in the as-forged state was hot compressed to various strain levels at a temperature of 350 °C and a strain rate of 10 s⁻¹. Heterogeneous deformation and dynamic recrystallization (DRX) behaviors of the complicated microstructures in the deformed samples were analyzed via a grain-partitioning approach based on intra-grain misorientation analysis from electron back-scattered diffraction (EBSD). The ZK30 alloy showed excellent formability, remaining intact at a true strain of −1.11. Continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) via grain boundary corrugation/bulging are the dominant mechanisms for the relaxation of strain energy during hot compression. Initial Zr-rich coarse grains undertook a significant portion of the plastic strain as the compression progressed, reflected by the increased misorientations within their interior and marked change in their aspect ratios. The results indicate that the excellent plasticity of the as-forged ZK30 alloy can be attributed to the operative CDRX mechanisms and the reduced deformation anisotropy of Zr-rich coarse grains containing Zn–Zr nano–precipitates.

Mg-Alloys for Forging Applications-A Review

Interest in magnesium alloys and their applications has risen in recent years. This trend is mainly evident in casting applications, but wrought alloys are also increasingly coming into focus. Among the most common forming processes, forging is a promising candidate for the industrial production of magnesium wrought products. This review is intended to give a general introduction into the forging of magnesium alloys and to help in the practical realization of forged products. The basics of magnesium forging practice are described and possible problems as well as material properties are discussed. Several alloy systems containing aluminum, zinc or rare earth elements as well as biodegradable alloys are evaluated. Overall, the focus of the review is on the process control and processing parameters, from stock material to finished parts. A discussion of the mechanical properties is included. These data have been comprehensively reviewed and are listed for a variety of magnesium forging alloys.

Effects of T5 Treatment on Microstructure and Mechanical Properties at Elevated Temperature of AZ80-Ag Alloy

Effects of T5 treatment on microstructure and mechanical properties at elevated temperature of hot-ring-rolled (HRRed) AZ80-Ag magnesium alloy were systematically investigated. Results show that, after aging at 175 °C for 36 h, discontinuous and continuous precipitates form inside grains, with the former one taking up a volume fraction of ~64.9%. T5 treatment improves the tensile strength at ambient temperature of the alloy but weakens its tensile strength and creep resistance at elevated temperatures (120–175 °C), indicating opposite effects of T5 on mechanical properties at ambient and elevated temperatures. During creep at 120–175 °C and under 70–90 MPa, the dynamic precipitation process in HRRed specimen is accelerated with increasing temperature. At 150–175 °C massive nucleation and growth of dynamic discontinuous precipitates could result in an atypical primary creep stage, consisting of deceleration and acceleration creep stages, which is reported in wrought Mg-Al-based alloy for the first time. Such primary creep stage can be eliminated by T5 treatment. Besides, diffusion-controlled dislocation creep is the dominant creep mechanism for both HRRed and T5 specimens.

Microstructure and Hot Deformation Behavior of Twin Roll Cast Mg-2Zn-1Al-0.3Ca Alloy

In the present work, the microstructure, texture, mechanical properties as well as hot deformation behavior of a Mg-2Zn-1Al-0.3Ca sheet manufactured by twin roll casting were investigated. The twin roll cast state reveals a dendritic microstructure with intermetallic compounds predominantly located in the interdendritic areas. The twin roll cast samples were annealed at 420 °C for 2 h followed by plane strain compression tests in order to study the hardening and softening behavior. Annealing treatment leads to the formation of a grain structure, consisting of equiaxed grains with an average diameter of approximately 19 µm. The twin roll cast state reveals a typical basal texture and the annealed state shows a weakened texture, by spreading basal poles along the transverse direction. The twin roll cast Mg-2Zn-1Al-0.3Ca alloy offers a good ultimate tensile strength of 240 MPa. The course of the flow curves indicate that dynamic recrystallization occurs during hot deformation. For the validity range from 250 °C to 450 °C as well as equivalent logarithmic strain rates from 0.01 s⁻¹ to 10 s⁻¹ calculated model coefficients are shown. The average activation energy for plastic flow of the twin roll cast and annealed Mg-2Zn-1Al-0.3Ca alloy amounts to 180.5 kJ/mol. The processing map reveals one domain with flow instability at temperatures above 370 °C and strain rates ranging from 3 s⁻¹ to 10 s⁻¹. Under these forming conditions, intergranular cracks arose and grew along the grain boundaries.

Bending Properties of Mg Alloy Tailored Arc-Heat-Treated Blanks

Tailored heat-treated blank is a special kind of sheet, and the plastic forming ability can be improved. In this work, the poor room-temperature plasticity of a tailored magnesium alloy blank was address through arc heat treatment. The formability of the material was enhanced through local modification with arc pretreatment. The plasticity of the tailored arc-heat-treated blank was verified through the V-bending test. The microstructure and mechanical properties of the blank were tested, and the mechanisms underlying its improved deformability were analyzed. The bendability of the blank first increased and then decreased as heat input increased. The maximum V-bending ability of the arc-heat-treated blank increased by 88% relative to that of the untreated blank. Although springback decreased under increasing heat input, the local strength and elastic modulus of the alloy blank were equivalent to those of the base metal. This result indicated that the springback resistance of the material did not improve. The back of the blank treated under the optimal parameters comprised heat-affected zones with good plasticity. Recrystallization and grain growth occurred in the heat-affected zones. The blank exhibited reduced hardness and improved malleability. When the heat input was further increased, however, a semi-melting zone formed on the lower surface of the blank. The formation of this zone resulted in the precipitation of intermetallic compounds from the crystal phase and increased the hardness of the blank. It also decreased the plasticity and malleability of the blank.

High Performance Fine-Grained Biodegradable Mg-Zn-Ca Alloys Processed by Severe Plastic Deformation

The tensile strength, fatigue, and corrosion fatigue performance of the magnesium alloy ZX40 benefit strongly from hybrid deformation processing involving warm equal-channel angular pressing (ECAP) at the first step and room temperature rotary swaging at the second. The general corrosion resistance improved as well, though to a lesser extent. The observed strengthening is associated with a combined effect of substantial microstructure refinement down to the nanoscale, reducing deformation twinning activity, dislocation accumulation, and texture transformation. The ultimate tensile strength and the endurance limit in the ultrafine-grained material reached or exceeded 380 and 120 MPa, respectively, which are remarkable values for this nominally low strength alloy.