Recent research progress on magnesium alloys in Korea:A review

This review highlights the recent advancements in Mg research in South Korea with a prime focus on high-speed-extrudable Mg–Bi-based alloys for high productivity and strength, innovative techniques utilizing {10–12} twinning for improved mechanical properties, and alloying and processing methods for enhanced corrosion resistance. High-alloyed Mg–Bi-based alloys possess thermally stable α-Mg matrix and secondary phase, which ensures high-speed extrusion of these alloys at elevated temperatures without hot cracking. Consequently, they exhibit outstanding extrudability with a maximum extrusion speed of up to 70 m/min. Furthermore, their high alloying contents offer excellent strength even after high-speed extrusion through strong solid solution hardening and particle hardening effects, making them suitable for high-performance extruded Mg products. The pre-twinning process utilizing {10–12} twinning and the combined process of pre-twinning and subsequent annealing have shown promise in controlling microstructure and texture of wrought Mg alloys and thus enhancing their mechanical properties. The pre-twinning process enhances tensile strength, fatigue properties, and age-hardening rate of Mg alloys. Furthermore, the combined processes of pre-twinning and subsequent annealing considerably improve their ductility, stretch formability, bending formability,and damping capacity. Efforts have been made to improve the corrosion resistance of Mg alloys through alloying additions, process treatments,and surface coatings. Alloying elements like Ca, Sc, and Sm alter the microstructural features(such as secondary phases and grain size)that affect the corrosion phenomenon. Process treatments such as multidirectional forging, screw rolling, and pulse electron beam can also improve the corrosion resistance by refining the microstructure. Furthermore, advanced surface coating technologies can create durable and corrosion-resistant layers for effectively protecting the Mg alloys. All these research activities conducted in South Korea have considerably contributed to the widespread utilization of Mg alloys in diverse applications by overcoming the inherent limitations of Mg alloys such as low extrudability, formability, and corrosion resistance.

Enhanced oxidation and overheating resistance of the extruded Mg–Zn–Al–Mn magnesium alloy by Calcium addition

The effects of Ca addition on the microstructure and oxidation properties of a new Mg alloy were studied.The oxidation behavior of the alloys was analyzed by thermal analysis and material characterization of the alloys exposed in flame environment;and both electrical and induction furnaces.Moreover,the surface layers were characterized using field emission scanning electron microscopy,and X-ray diffraction technique.It was found that increasing the Ca addition reduces the grain size and increases the fraction of the secondary phases,and enhances the mechanical properties.Moreover,increasing the Ca contents resulted in the formation of a dense CaO/MgO layer on the surface prohibited the oxygen diffusion and assisted in protection of the substrate against further oxidation.Therefore,ignition temperature was increased from 680℃ to 890℃ after addition of the Ca element.The mechanical properties and ignition behavior of the current materials was compared with the literature which it showed an excellent combination of the properties in the developed alloys.

Effects of temperature on critical resolved shear stresses of slip and twining in Mg single crystal via experimental and crystal plasticity modeling

Magnesium(Mg)single crystal specimens with three different orientations were prepared and tested from room temperature to 733 K in order to systematically evaluate effects of temperature on the critical resolved shear stress(CRSS)of slips and twinning in Mg single crystals.The duplex non-basal slip took place in the temperature range from 613 to 733 K when the single crystal samples were stretched along the<0110>direction.In contrast,the single basal slip and prismatic slip were mainly activated in the temperature range from RT to 733 K when the tensile directions were inclined at an angle of 45°with the basal and the prismatic plane,respectively.Viscoplastic self-consistent(VPSC)crystal modeling simulations with genetic algorithm code(GA-code)were carried out to obtain the best fitted CRSSs of major deformation modes,such as basal slip,prismatic slip,pyramidalⅡ,{1012}tensile twinning and{1011}compressive twinning when duplex slips accommodated deformation.Additionally,CRSSs of the basal and the prismatic slip were derived using the Schmid factor(SF)criterion when the single slip mainly accommodated deformation.From the CRSSs of major deformation modes obtained by the VPSC simulations and the SF calculations,the CRSSs for basal slip and{1012}tensile twinning were found to show a weak temperature dependence,whereas those for prismatic,slip and{1011}compressive twinning exhibited a strong temperature dependence.From the comparison of previous results,VPSC-GA modeling was proved to be an effective method to obtain the CRSSs of various deformation modes of Mg and its alloys.

Unveiling the planar deformation mechanisms for improved formability in pre-twinned AZ31 Mg alloy sheet at warm temperature

To investigate the role of pre-twins in Mg alloy sheets during warm planar deformation, the stretch forming is conducted at 200 ℃. Results suggest the formability of the pre-twinned AZ31 Mg alloy sheet is enhanced to 11.30 mm. The mechanisms for the improved formability and the deformation behaviors during the planar stretch forming are systematically investigated based on the planar stress states. The Schmid factor for deformation mechanisms are calculated, the results reveal that planar stress states extremely affect the Schmid factor for {10-12}twinning. The detwinning is activated and the prismatic slip is enhanced in the pre-twinned sheet, especially under the planar extension stress state in the outer region. Consequently, the thickness-direction strain is accommodated better. The dynamic recrystallization(DRX) type is continuous DRX(CDRX) regardless of the planar stress state. However, the CDRX degree is greater under the planar extension stress state.Some twin lattices deviate from the perfect {10-12} twinning relation due to the planar compression stress state and the CDRX. The basal texture is weakened when the planar stress state tends to change the texture components.

Nd添加结合热挤压制备Mg-Gd-Zr合金的力学性能

研究添加钕元素对挤压态Mg-9Gd-0.5Zr(质量分数,%)合金显微组织和力学性能的影响。在673 K下对Mg-9Gd-0.5Zr和Mg-9Gd-2Nd-0.5Zr两种合金进行挤压。添加钕后,组织中被拉长的非动态再结晶晶粒消失,获得均匀分布的动态再结晶晶粒,晶粒尺寸为1.68μm。此外,在挤压态Mg-9Gd-2Nd-0.5Zr合金中动态析出大量的纳米Mg5(Gd, Nd)颗粒,通过Orowan强化机制有效地提高合金的强度。细小的纳米颗粒通过阻碍形变能的释放为动态再结晶过程提供形核,进一步促进动态再结晶的进行。而且,动态再结晶晶粒具有弱织构,对塑性的提高起重要作用。因此,添加钕能够同时提高挤压态Mg-9Gd-0.5Zr合金的强度和伸长率。

Corrosion behavior of Mg-Mn-Ca alloy:Influences of Al,Sn and Zn

The effects of different elements including Al,Sn and Zn with ability of solution hardening on corrosion behavior of a Mg alloy have been studied.The microstructure was analyzed and the electrochemical and immersion techniques were used for corrosion studies.Scanning kelvin probe force microscopy(SKPFM)was utilized to analyze the volta-potential distribution on the surface.It was found that all additives reduced the corrosion resistance;however,Zn decreased the corrosion resistance less than Al and Sn.The corrosion rate was quantitatively explained through volta-potential difference and the second phase fraction.

Formulation of corrosion rate of magnesium alloys using microstructural parameters

Up to the date of writing this article,a quantitative analysis between corrosion rate and combined microstructural parameters including composition,grain size,and precipitations has not been reported.Hence,a literature review was carried out on these parameters to understand the quantitative effect of each one on the corrosion rate of Mg and Mg alloys.Moreover,using the available data in the literature and several experimental results,a new model was developed to predict the corrosion rate,through microstructural parameters.This model suggests that by using ultra-fined grains,alloying compounds with low Volta-potential difference relative to the matrix and a low fraction of secondary phase,a very low corrosion rates of materials are achievable.

高压铸造Al-6Si-3Ni及Al-6Si-3Ni-2Cu合金在NaCl水溶液中的抗腐蚀性能（英文）

研究高压铸造Al-6Si-3Ni(SN63)及Al-6Si-3Ni-2Cu(SNC632)合金在3.5%(质量分数)NaCl水溶液中的腐蚀行为。X射线衍射及显微组织分析表明,单相Si及Al3Ni/Al3Ni2二元相分布在合金的晶界处,并且在SNC632合金晶界处析出单相Cu。电化学腐蚀实验结果表明,与SN63合金相比,SNC632合金表现出高的腐蚀电位(φcorr),低的腐蚀电流密度(Jcorr)及高的耐腐蚀性。电化学阻抗谱(EIS)等效电路曲线拟合分析表明,电解质与衬底之间存在两个界面,而SNC632合金的电荷转移电阻(Rct)要比SN63合金的高。浸泡腐蚀试验与电化学腐蚀结果一致,SNC632合金表现出较高的耐腐蚀性。Cu元素的添加导致在SNC632合金并未出现含金属间化合物的次生铜相而出现单相Cu,进而提高其抗腐蚀性。

Microstructural evolution and mechanical properties of binary Mg-xBi(x=2,5,and 8 wt%)alloys

The microstructures and mechanical properties of Mg-x Bi(x=2,5,and 8 wt%)were investigated compared with pure Mg.The ascast Mg-Bi billets consist of dendriticα-Mg grain matrix,divorced eutectic Mg_(3)Bi_(2) phase and secondary precipitated Mg_(3)Bi_(2) phase.After homogenization,secondary precipitated Mg_(3)Bi_(2) particles were all dissolved into the matrix,while most of the divorced eutectic Mg_(3)Bi_(2) intermetallic compounds retained.All the as-extruded samples exhibit fully dynamic recrystallization(DRX)and the average grain size decreases and the amount of nano-scale Mg_(3)Bi_(2) precipitates increases with increasing Bi content.Additionally,Bi alloying has little influence on the texture of the as-extruded pure Mg,with all the samples showing typical basal texture.As the results of grain refinement and precipitation hardening,the strengths of the as-extruded samples increase under both tensile and compressive tests.Besides,the yield asymmetry significantly decreases with Bi content.Moreover,all the as-extruded samples represent similar ductility under compression,while the tensile elongation first increases and then decreases with more Bi added.The as-extruded Mg-5Bi alloy demonstrates good combination of strength and ductility.However,Mg-8Bi alloy displays lower tensile ductility than that of Mg-5Bi alloy due to the presence of abundant undissolved coarse Mg_(3)Bi_(2) particles,which act as cracking sources during tensile test.Furthermore,the strain hardening rate,strain hardening exponent n,and hardening capacity Hc are greatly reduced by Bi addition,mainly owing to the enhanced synergy effects of grain refinement and numerous Mg_(3)Bi_(2) precipitates.

Efect of Pre‑stretch Strain at High Temperatures on the Formability of AZ31 Magnesium Alloy Sheets

High-temperature pre-stretching experiments were carried out on the AZ31 Mg alloy at 723 K with strain levels of 2.54%,6.48%,10.92%,and 19.2%to alter the microstructure and texture for improving room-temperature formability.The results showed that the strain-hardening coefcient increased,while the Lankford value decreased.In addition,the Erichsen values of all pre-stretch sheets were enhanced compared with that of the as-received sheet.The maximum Erichsen value increased from 2.38 mm for the as-received sample to 4.03 mm for the 10.92%-stretched sample,corresponding to an improvement of 69.32%.This improvement was mainly attributed to the gradual increase in grain size,and the(0001)basal texture was weakened due to the activated non-basal slip as the high-temperature pre-stretching strain levels increased.The visco-plastic self-consistent analysis was performed on the as-received and high-temperature pre-stretched samples.Results confrmed the higher activity of the prismatic slip in 10.92%-stretched sample,leading to divergence and weakening of basal texture components.This results in an augmentation of the Schmid factor under diferent slip systems.Therefore,it can be concluded that high-temperature pre-stretching technology provided an efective method to enhance the formability of Mg alloy sheets.

Recent Progress and Development in Extrusion of Rare Earth Free Mg Alloys: A Review

Mg and its alloys are the lightest structural metals available and are extremely attractive for applications as lightweight components, particularly in the automobile, electronic, and aerospace industries. The global market for wrought Mg alloys has steadily expanded over the past decade. And numerous studies have been carried out to meet this increasing demand of high-performance Mg alloys. However, Mg extrusion alloys have had a very limited usage so far. To overcome existing industrial challenges, one desirable approach is the development of low-cost rare earth(RE) free Mg extrusion alloys with superior mechanical properties. This review will introduce the recent research highlights in the extrusion of Mg alloys, specifi cally focusing on low-cost RE-free Mg alloy. The results from both the literature and our previous study are summarized and critically reviewed. Several aspects of RE-free Mg extrusion alloys are described in detail:(1) novel alloying designs including Mg–Al-, Mg–Zn-, Mg–Ca-, Mg–Sn-, and Mg–Bi-based alloys,(2) advanced extrusion techniques, and(3) extrusion-related severe plastic deformation(SPD) processing. Accordingly, considering the large gap in mechanical properties between the current RE-free Mg alloys and high-performance aluminum alloys, new alloy design, processing route control, and recommendations for future research on RE-free Mg extrusion alloys are also proposed. We hope this review will not only off er insightful information regarding the extrusion of RE-free Mg alloys but also inspire the development of new Mg extrusion technologies.