This study investigates the effect of Zn addition (1, 5, and 10 wt.%) to the Mg melt on the microstructure and mechanical properties of Mg–Ti composites fabricated via liquid metal dealloying (LMD). The addition of Zn effectively refines the Ti matrix while preserving the characteristic three-dimensional bicontinuous structure of dealloyed composites. Quantitative analysis shows that increasing Zn content reduces the Ti matrix width and effective grain size by up to 18% and 44%, respectively. Microstructural observations further reveal the formation of lamellar {11–22} contraction twins within the Ti matrix, with twin density increasing proportionally with Zn addition in the absence of external mechanical loading. As a result, the Vickers hardness increases monotonically from 130 HV in the Zn-free composite to 203 HV in the Mg–10Zn composite, corresponding to a 56% improvement. These results demonstrate that Zn alloying of the Mg melt is an effective strategy for enhancing the mechanical performance of bicontinuous Mg–Ti composites produced by LMD.

This study compares the microstructural evolution, dynamic recrystallization (DRX) behavior, tensile properties, and age-hardenability between the newly developed high-speed-extrudable BA56 alloy and those of the widely recognized AZ31 alloy in industry. Unlike the AZ31 alloy, which retains partially unrecrystallized grains, the high-speed-extruded BA56 alloy demonstrates a coarser but entirely recrystallized and more homogeneous microstructure. The fine-grained structure and abundant Mg₃Bi₂ particles in the BA56 extrusion billet significantly enhance its DRX behavior, thus enabling rapid and complete recrystallization during extrusion. The BA56 alloy contains band-like fragmented Mg₃Bi₂ particles and numerous fine Mg₃Bi₂ particles distributed throughout the material, in contrast to the sparse Al₈Mn₅ particles in the AZ31 alloy. These features contribute to superior mechanical properties of the BA56 alloy, which achieves tensile yield and ultimate tensile strengths of 205 and 292 MPa, respectively, compared to 196 and 270 MPa for the AZ31 alloy. The superior strength of the BA56 alloy, even with its coarser grain size, can be explained by its elevated Hall-Petch constant and the strengthening contribution from the fine Mg₃Bi₂ particles. Additionally, the BA56 alloy demonstrates significant age-hardenability, achieving a 22% enhancement in hardness following T5 aging, attributed to the precipitation of nanoscale Mg₃Bi₂ and Mg₁₇Al₁₂ phases. By contrast, the AZ31 alloy shows minimal hardening due to the absence of precipitate formation during aging. These findings suggest that the BA56 alloy is a promising candidate for the production of extruded Mg components requiring a combination of high productivity, superior mechanical performance, and wide-ranging process adaptability.

Metal composites produced through the liquid metal dealloying (LMD) process feature an advanced matrix-matrix composite structure, where two metallic materials form a continuous, three-dimensional interconnected network. This study investigates the effects of TiCu precursor compositions on dealloying behavior and microstructural evolution in liquid Mg, using Ti₅₀Cu₅₀ and Ti₃₀Cu₇₀ precursors. The initial microstructure of the precursor significantly influences dealloying kinetics and phase transitions. The single-phase Ti₅₀Cu₅₀ precursor exhibits a faster initial dealloying rate due to its homogeneous structure, yet complete dealloying requires 90 min. In contrast, the dual-phase Ti₃₀Cu₇₀ precursor achieves complete dealloying in 30 min, demonstrating the impact of a higher Cu concentration on accelerating the process kinetics. Additionally, the study explores the coarsening behavior and hardness variations during the LMD process, along with the microstructural characteristics of Mg-Ti composites fabricated from these two precursors. The findings highlight the critical role of precursor composition in tailoring the microstructure and properties of Mg-Ti composites produced through the LMD process, demonstrating its potential for advanced composite material manufacturing.

This study investigates the effect of the deformation mode on the precipitation behavior of an extruded Mg–8.0Al–0.5Zn–0.2Mn (AZ80) alloy. The alloy samples are compared after the application of 3.5% tension and 3.5% compression along the extrusion direction to induce slip-dominant and twinning-dominant deformation modes, respectively. The pre-compressed (PC) sample, which contained numerous {10–12} tension twins, has a reduced grain size and a higher internal strain than the pre-tensioned (PT) sample, which is attributed to the inherent internal strain that occurs during the formation and growth of the twins. As a result, the precipitation behavior of the PC sample is accelerated, leading to its short peak aging time of 32 h, which is lower than those of the PT and as-extruded samples (48 and 100 h, respectively). Furthermore, fine continuous precipitates (CPs) rapidly form within the {10–12} twins, contributing to the enhanced hardness. Discontinuous precipitates (DPs), which have a hardness comparable to the CP-containing twinned regions, in the PC sample experience less coarsening during aging than those in the PT sample due to growth inhibition by the {10–12} twins. Ultimately, the {10–12} twins generated under the twinning-dominant deformation condition lead to enhanced precipitation behaviors, including the preferential formation and refinement of CPs and the suppressed coarsening of DPs. Consequently, pre-deformation that occurs {10–12} twinning exhibits more pronounced effects on precipitation acceleration and microstructural modification than slip-inducing pre-deformation.

This review article provides overall understanding of stainless, environment-friendly, and nonflammable Mg alloys (SEN alloys) recently developed at the Korea Institute of Materials Science. SEN alloys are produced by adding small amounts of Ca and Y (each < 1 wt%) into commercial Mg–Al based alloys, resulting in exceptional ignition and corrosion resistances and impressive mechanical properties. Their main advantages of SEN alloys are as follows. (1) A dense multi-oxide layer of SEN alloys comprising MgO, CaO, and Y₂O₃ impedes the outward dispersion of Mg vapor and the inward penetration of O₂ during oxidation, thereby enhancing the oxidation and ignition resistances. (2) The presence of Ca- and Y-based second-phase particles in SEN alloys can enhance their corrosion resistance because Ca-containing particles prevent the spread of corrosion, and the replacement of Al-containing particles with less noble ones containing Y (e.g., Al–Mn–Y or Al–Y particles) retards corrosion. (3) The addition of minor amounts of Ca and Y renders excellent mechanical properties due to improved strengthening effects. These enhanced properties are attributed to more pronounced dynamic recrystallization and grain refining behaviors caused by the second-phase particles during extrusion. (4) Despite the presence of various types of second-phase particles, the fatigue properties of SEN9 alloys are similar to those of commercial AZ91 alloys. (5) Simultaneous introduction of Ca and Y suppresses the formation of Mg₁₇Al₁₂ discontinuous precipitates during aging, leading to the enhanced elongation of aged SEN alloys. (6) Adding mischmetal into the SEN9 alloy leads to a six-fold enhancement in extrudability. Consequently, the studies conducted on SEN alloys demonstrate their excellent ignition and corrosion resistances and mechanical properties, which broaden the industrial applications of Mg alloys by addressing their inherent weaknesses.

This study investigates the effect of characteristics and distribution of Mg₁₇Al₁₂ precipitates on the uniaxial tensile and three-point bending properties of extruded Mg alloys containing high Al contents. The extruded Mg–9Al–1Zn–0.3Mn (AZ91) alloy contains lamellar-structured Mg₁₇Al₁₂ discontinuous precipitates along the grain boundaries, which are formed via static precipitation during natural air cooling. The extruded Mg–11Al–1Zn–0.3Mn (AZ111) alloy contains spherical Mg₁₇Al₁₂ precipitates at the grain boundaries and inside the grains, which are formed via dynamic precipitation during extrusion. Due to inhomogeneous distribution of precipitates, the AZ111 alloy consists of two different precipitate regions: precipitate-rich region with numerous precipitates and finer grains and precipitate-scarce region with a few precipitates and coarser grains. The AZ111 alloy exhibits a higher tensile strength than the AZ91 alloy because its smaller grain size and more abundant precipitates result in stronger grain-boundary hardening and precipitation hardening effects, respectively. However, the tensile elongation of the AZ111 alloy is lower than that of the AZ91 alloy because the weak cohesion between the dynamic precipitates and the matrix facilitates the crack initiation and propagation. During bending, a macrocrack initiates on the outer surface of bending specimen in both alloys. The AZ111 alloy exhibits higher bending yield strength and lower failure bending strain than the AZ91 alloy. The bending specimens of the AZ91 alloy have similar bending formability, whereas those of the AZ111 alloy exhibit considerable differences in bending formability and crack propagation behavior, depending on the distribution and number density of precipitates in the specimen. In bending specimens of the AZ111 alloy, it is found that the failure bending strain (ε_{f, bending}) is inversely proportional to the area fraction of precipitates in the outer zone of bending specimen (A_ppt), with a relationship of ε_{f, bending} = –0.1A_ppt + 5.86.

This study presents a novel process for the fabrication of metal–intermetallic composites with a 3D bicontinuous structure, achieved through a combination of liquid metal dealloying (LMD) and subsequent alloying. Initially, porous Ti structures are produced using the LMD process, followed by immersion in a molten Mg–3Al (wt%) metal. Due to the higher thermodynamic miscibility of Al with Ti compared to Mg, the concentration of Al in the Ti matrix increases as the immersion time increases. This results in a sequential phase transition within the Ti matrix: α-Ti → Ti₃Al → TiAl. The phase transition considerably affects the hardness and strength of the composite material, with the Mg–Ti₃Al–TiAl composite exhibiting a maximum hardness nearly twice as high as that of the conventional Mg–Ti composite. This innovative process holds potential for the development of various bicontinuous metal–intermetallic composites.

This study investigates the effect of {10–12} deformation twins on the continuous precipitation behavior of an extruded Mg–8.0Al–0.5Zn–0.2Mn (AZ80) alloy during aging. The extruded AZ80 alloy is compressed along the transverse direction to introduce {10–12} twins, followed by an aging treatment at 300 °C. The extruded material exhibits a twin-free microstructure with low internal strain energy, whereas the pre-twinned material possesses abundant {10–12} twins and has high internal strain energy. The aging results reveal that the peak-aging time of the pre-twinned material (1 h) is one-eighth of that of the extruded material (8 h). Although Mg₁₇Al₁₂ continuous precipitates (CPs) are observed in both the peak-aged materials, these CPs are much smaller and more densely distributed in the pre-twinned material despite the significantly shorter aging time. The CPs size in the peak-aged materials increases in the following order: twinned region in the pre-twinned material (0.47 µm) < residual matrix region in the pre-twinned material (1.71 µm) < matrix region in the extruded material (2.55 µm). Moreover, the CPs number density in the twinned region of the pre-twinned material is approximately 11 times higher than that in the matrix region of the extruded material. The peak-aged pre-twinned material exhibits significantly higher tensile strength and ductility than the peak-aged extruded material. These results demonstrate that the formation of {10–12} twins in the extruded AZ80 alloy substantially accelerates the static precipitation of CPs during aging at 300 °C and improves the tensile properties of the peak-aged material.

This study investigates the variations in the microstructural characteristics of a pre-twinned Mg alloy with the temperature of the subsequent annealing treatment. To this end, a rolled AZ31 alloy is compressed to 3% plastic strain along the rolling direction (RD) to activate {10-12} twinning and is subsequently annealed at 200, 250, 300, 350, and 400 ℃. Numerous {10-12} twins are formed throughout the compressed material, leading to the formation of a RD-oriented texture. At an annealing temperature of 200 ℃, no microstructural variations occur during annealing. As the annealing temperature increases from 250 to 400 ℃, the residual strain energy and remaining twin boundaries of the annealed material decrease owing to the promoted static recovery and the increased area fraction of twin-free grown grains. Consequently, an increase in the annealing temperature results in a gradual microstructural transition from a fully twinned grain structure to a completely twin-free grain structure. The microstructural evolution during annealing is predominantly governed by the movement of high-angle grain boundaries via a strain-induced boundary migration mechanism, and a few twin boundaries migrate above 350 ℃ because of their lower boundary energy. The boundary migration behavior and resultant microstructural evolution are discussed in detail based on the variations in boundary mobility and driving force for boundary migration with annealing temperature.

This study investigates the effects of extrusion temperature on the dynamic recrystallization (DRX) behavior of a Mg–3Al–1Zn–0.3Mn (AZ31, wt%) alloy during hot extrusion and on the microstructural characteristics and mechanical properties of materials extruded at 350 and 450 ℃. An increase in the extrusion temperature causes a decrease in the amount of strain energy accumulated in the material during extrusion, because of promoted activation of pyramidal <c + a> slip and dynamic recovery. This reduced strain energy weakens the DRX behavior during extrusion, which eventually results in a decrease in the area fraction of recrystallized grains of the extruded material. The material extruded at 450 ℃ has coarser grains and a stronger basal fiber texture than that extruded at 350 ℃. As the extrusion temperature increases from 350 to 450 ℃, the tensile yield strength (TYS) of the extruded material increases from 191.8 to 201.5 MPa, whereas its compressive yield strength (CYS) decreases from 122.5 to 111.0 MPa; consequently, its tension–compression yield stress ratio (CYS/TYS) decreases from 0.64 to 0.55. The increase in the TYS is attributed mainly to the stronger texture hardening and strain hardening effects of the extruded material, and the decrease in the CYS is attributed to the reduced twinning stress resulting from grain coarsening and texture intensification. The microstructural and textural evolutions of the materials during extrusion and the deformation and hardening mechanisms of the extruded materials are discussed in detail.