Recent legislative and environmental pressures on the automotive industry to produce light-weight fuel efficient vehicles with lower emissions have led to a requirement for traditional steel components to be replaced by advanced materials such as aluminum, magnesium and metal matrix composites. This has led to a complete re-analysis of engineering design and manufacturing routes, with the emergence of advanced technologies as a viable process for the production of high volume, low cost, high integrity automotive components. Here we present a general review of the application of magnesium alloys for the automotive components. We will also discuss the research activities and application of magnesium alloys and key technologies including the successful development of magnesium seat frame described and discussed in terms of vehicle performance and casting qualities introduced in vehicles developed by the Hyundai and Kia motors corporation (HKMC).

Superplastic magnesium alloy sheets were closed-die forged into an experimental part with ribs, which are asymmetrical elements to the plane of the forging. A macroscopic surface defect, which was formed by extrusion-type flow, was observed opposite to the rib during forging under improper lubrication conditions. However, the formation of the defect could be successfully suppressed by changing the frictional conditions of the workpiece/dies interface. Analysis of the rib forging using a finite controlled volume method simulation suggested that the suppression of the extrusion-type defect is associated with a change in velocity field distribution of the deforming material.

Die-cast plates of ASTM (American Society for Testing and Materials) AZ91D magnesium alloy were anodized by DC or AC electrolysis in a solution of phosphate and ammonium salt in which the anodized layer is formed by local discharge, followed by rapid solidification. Salt spray tests of the anodized specimens showed that AC electrolysis increases corrosion resistance and the anodized layers become denser compared with that for DC electrolysis. Tensile strength, elongation, and hardness were also improved by anodization, but higher anodizing bias and the resulting heating caused grain coarsening and a decrease in these properties. For the specimens that displayed remarkable improvement in mechanical properties, a decrease in network precipitates of the β phase was observed. Improvement of mechanical properties is considered to be due to the fine precipitation of β inside the grains of the α phase at moderate temperature.

To shorten the press forming and surface treatment process for AZ31 magnesium alloy by eliminating the need for mechanical polishing of the press-formed surface, we determined the necessary value of surface roughness, Ra, for developing a luster on surface with or without acid aqueous solution treatment. The target value for the gloss of AZ31 magnesium alloys was set to be that of the surface after mechanical polishing by using emery paper #2000. To achieve this gloss solely by mechanical polishing without acid aqueous solution treatment, the surface roughness, Ra, had to be less than 0.2 μm. If the acid aqueous solution treatment was applied to the mechanically polished surface, the necessary surface roughness, Ra, before the treatment was 1.5 μm. The increase in gloss as a result of acid aqueous solution treatment results from smoothing of small surface convexo-concave features measuring less than 0.2 μm. Because the surface roughness, Ra, of articles press-formed by using 100,000 times square-cup drawings was 0.3 μm, the mechanical polishing stage could be eliminated from the process for developing a luster, and the acid aqueous solution treatment could be applied directly.

Effects of 2 mass% Li addition on the AZ80 Mg alloy are investigated, including crystal structures, mechanical properties and corrosion resistance. Experimental results show that the density of AZ80 Mg alloy can be reduced to be 1.71 g/cm³ by addition of 2 mass% Li. Both the AZ80 and AZ80-2%Li Mg alloys exhibit the two-phase microstructure with α and β phases. Adding 2 mass% Li to AZ80 Mg alloy can obviously increase the ductility and impact toughness, but reduce the corrosion resistance.

High temperature creep strength at 650 K and microstructures of Mg-Y-Zn-based alloys with fourth elements (nickel and calcium) have been investigated. The microalloying of 0.5 mass% calcium markedly increases the stacking fault density in the Mg-3 mass%Y-0.5 mass%Zn alloy. Furthermore, the addition of calcium can decrease the size of stacking faults. On the other hand, in the nickel-added alloy, many precipitates were formed and the estimated stacking faults density decreased significantly. The creep strength of the Mg-Y-Zn-Ca alloy is higher than that of the base alloy (Mg-3 mass%Y-0.5 mass%Zn, WZ305). Transmission electron microscopic (TEM) observations revealed that many a-dislocations on the basal planes in the magnesium matrix are extended during creep deformation in Mg-Y-Zn-based alloys. There was significant consumption of solute atoms in the matrix and deterioration of creep strength in the Mg-Y-Zn-Ni alloy, because the formation of a large number of precipitates began before creep. On the other hand, both the low mobile dislocation density and the large separation width of extended a-dislocations were observed in the Mg-Y-Zn-Ca alloy, which exhibits excellent creep strength at 650 K under 20 MPa.

Effects of the alloying element on processing of the environmental-friendly anodizing were investigated in various AZ series magnesium alloys. The phosphate solution was used mainly in the current process without the need for the deleterious materials such as heavy metals or fluoride. Also the characteristics of the formed coatings, such as their structure, composition, and corrosion resistance, were investigated. Anodized coatings became dense with increasing aluminum content of the alloy substrate. X-ray diffraction analysis revealed that the anodized coatings changed amorphous structure in the cases of the magnesium substrate containing aluminum concentration from 1 to 9 mass%. The anticorrosion performance of these coatings with an average thickness of 10 μm varied depending on the aluminum content, and it is concluded that the anticorrosion performance improved with increasing aluminum content except for the anodized AZ61 specimen.

The age hardening response and corrosion resistance of Mg-8%Gd-2%Nd-0.3%Zr alloys with various Zn contents up to 2% (in weight) have been investigated. The Zn-free alloy exhibits relatively lower age hardening and slower age response, whereas the addition of Zn enhances the age hardening response remarkably. The weight loss after salt spray test decreases with increasing Zn content in the peak-aged alloys, which is presumably associated with the increased amount of eutectic Mg-Zn-Nd-Gd phase acting as a corrosion barrier along the α grain boundaries. The potentiodynamic polarization curves reveal that with the increase in Zn content, the value of I_corr decreases gradually while the value of E_corr increases.

A study has been made on the effect of Sb and Sr on the microstructure and mechanical properties of Mg-Sn-Al-Si based (TAS) alloy. When Sb is added to TAS alloy, the morphology of second phase particles changes to fine radial shape by the formation of nucleation cores. Refined microstructure of TAS-Sb alloys results in higher yield strength and larger elongation with lower creep resistance than those of TAS alloy. Sr addition induces the formation of large amount of thermally stable second phase particles. Due to the large amount of thermally stable second phase particles, TAS-Sr alloys show superior creep resistance and higher yield strength at both room and high temperatures than those of TAS alloy.

The phase constitutions of Mg-Zn-Gd alloys in the Mg-rich corner were investigated using XRD, SEM and TEM. The effect of Zn/Gd ratio and content of Zn, Gd element on the phase constitutions of Mg-Zn-Gd alloys were studied. Formation range of I-phase in the Mg-Zn-Gd system in the Mg-rich corner has been confirmed using conventional cast process. I-phase could been formed for alloys in the range of Zn/Gd ratio from 1.5 to 40, or with Zn above 3 at.% under the condition of Zn/Gd ratio of 10 and 25.

The as-cast microstructure of Mg-5Al-3Ca-xY alloy consists of dendritic α-Mg matrix, (Mg, Al)₂Ca eutectic phase and Al₂Y intermetallic compounds. These two kind of (Mg, Al)₂Ca compounds were observed: coarse irregular-shape structure at grain boundary and fine needle-shape structure in the α-Mg matrix grain. This (Mg, Al)₂Ca phase of the extruded alloys was elongated to extrusion direction and size of this phase was refined comparing with that of as-cast alloys because of severe deformation during hot extrusion. Maximum yield and ultimate strength value of extruded alloys was 326 and 331 MPa at Mg-5Al-3Ca-3Y alloy, respectively. From these results, it is conclusively demonstrated that Y additions on Mg-5Al-3Ca alloy have more effect to improve mechanical properties.

Effect of rare-earth elements (Y and Dy) on the mechanical properties of Mg solid solution single crystal is investigated. Comparing with the effect of other elements reported by previous studies, the solid solution strengthening by Y and Dy are much higher than that of other additives such as Zn for basal slip operation, while the isotropic strain by Zn atoms is higher than those of Y and Dy. Strain-rate changing tests were conducted for a further understanding of the dislocation motion and it revealed that the activation volumes estimated for Mg alloys with Y and Dy are much smaller than that of Zn-added alloy, while the activation enthalpy is almost the same. It was confirmed that the high strengthening effect by Dy addition is also found by Y addition, while the elastic interaction based on neither isotropic or anisotropic distortion are sufficient to explain the origin of the strengthening effect by Y and Dy addition.

The effect of solution treatment before equal channel angular extrusion (ECAE) on the evolution of microstructures and mechanical properties in as-cast Mg-6.0Zn-0.6Y-0.5Zr alloy after different ECAE passes has been systematically investigated. The micrographs and tensile results showed that the solution treatment significantly influenced the microstructural evolution, as well as tensile strength and elongation. ECAE processing results in producing finer grain structure both in the as-cast and as-solutionized alloys when the passes increased. However, solution treatment before ECAE provides a significant increase in forming rate of fine recrystallized grains during ECAE at high temperature of 623 K. A fully recrystallized microstructure was observed after 8 passes in the as-solutionized alloy, while it was not finished even after 8 passes in the as-cast alloy. The ductility of as-solutionized alloy is always significantly better than those of the as-cast alloy. However, the strengths of the former are better than those of the later only after the passes beyond 6 passes.

Equal channel angular pressing (ECAP) is so far the most viable severe plastic deformation procedure to extrude material by using specially designed channel dies without any substantial changes in geometry and to prepare an ultrafine grained material. Magnesium is the lightest of all structural metallic materials, but a typical hard-to-deform metallic material due to its HCP structure and associated slip systems. ECAP has been applied for a processing method of severe plastic deformation to achieve grain refinement of magnesium and to enhance it’s low ductility. In particular, we investigated the deformation and fracture behavior of pure magnesium workpiece using experimental and numerical methods. The finite element method with different ductile fracture models was employed to simulate plastic deformation and fracture behavior of the workpiece.

In order to obtain high-quality products in powder metallurgy, it is important to control and understand the densification behavior of metallic powders. The effect of the powder characteristics of magnesium powders on the compaction behavior was investigated in this study by experimental and theoretical methods. A modified version of Lee-Kim’s plastic yield criterion, known as the critical relative density model, was applied to simulate the densification behavior of magnesium powders, and a new approach that extracts both the powder and the matrix characteristics was developed. The model was implemented via the finite element method, and powder compaction under upsetting conditions was simulated. The calculated and experimental results are in good agreement.

An AZ91 alloy pretreated by ultrasonic vibration (UV) was subjected to extrusion to refine the microstructure. The results indicated that the UV pretreatment had a strong influence on the microstructure evolution and mechanical properties of the extruded AZ91 alloy. With UV pretreatment, a fine and uniform microstructure with an average grain size of 13.5 μm was obtained, and the fraction of the fiber-like, partially-recrystallized, structure was markedly reduced. In addition to the superior mechanical properties such as a yield strength of 256 MPa, an ultimate tensile strength of 320 MPa and a fracture elongation of 9.7% were achieved in the extruded AZ91 alloy with UV pretreatment.

Strip casting process combines casting and hot rolling into a single step, with advantages of low equipment cost, low running cost, energy saving and space saving. Protective gases, such as SF₆ and Novec^TM612, should be used in order to prevent the ignition of magnesium alloys during strip casting. However, protective gases have disadvantages such as global warming, high production cost and corrosion of steel based equipments. According to the recent study, the addition of CaO is the effective way to improve the ignition and oxidation resistance of magnesium alloy. CaO added AZ31 magnesium alloy strip casting could be manufactured with reduced protective gas during melting and without protective gas during strip casting. The minimum SF₆ gas amount could be reduced under 50 ppm for 0.3 mass%CaO added AZ31 magnesium alloy both under sealed and unsealed conditions. The strips of CaO added AZ31 magnesium alloys were almost uniform in terms of microstructure and hardness.

Mg_97.3Zn_2.3Y_0.4 alloy has been subjected to twin-roll casting (TRC) process. As-cast microstructure consists of α-Mg dendrite and icosahedral interdendritic phase. The icosahedral phase present in TRC alloy is found to be thermally unstable and transforms to H-phase and W-phase during subsequent thermo-mechanical treatment (TMT) at 400°C. It shows that the pre-heating condition has a significant effect on the microstructural evolution during TMT. The specimen pre-heated at 400°C for 30 min shows elongated microstructure after TMT, while the specimen pre-heated at 400°C for 12 h shows equiaxed recrystallized structure after TMT. Such homogeneous microstructure of the specimen pre-heated at 400°C for 12 h results in better combinations of strength and ductility than the specimen pre-heated at 400°C for 30 min.

The heat treatment parameters of AZ64 magnesium alloy have been optimized using thermal analysis, scanning electron microscopy and X-ray diffraction techniques. The thermal analysis result revealed that two precipitation reactions took place during the solidification of AZ64 alloy. Therefore, a two-step solution heat treatment method, instead of traditional solution treatment whose temperature was about 10°C below the solidus temperature, was developed corresponding to the dissolution of two precipitate phases. With comparison to the traditional heat treatment, the two-step treatment method could generate a complete solution effect. During the following aging process, precipitates almost uniformly dispersed throughout the matrix, thus improve the tensile strength of alloy.

Microstructure evolutions of rapidly-solidified (RS) ribbon and conventionally cast bulk Mg-1 at%Zn-2 at%Y alloys have been studied by transmission electron microscopy (TEM), particularly focusing on formation process and phase stability of the long-period structures. It is found that there are significant differences in microstructural evolutions between the RS ribbon and the cast-bulk alloys, in terms of thermal stability of the long-period phases at temperatures higher than 673 K. For both the as-quench ribbon and the as-cast bulk specimens, 18R-type long-period phase is dominantly observed at grain boundaries. After annealing at temperatures higher than 673 K, the long-period phases at grain boundaries in the RS ribbon almost disappear to form Mg₂₄Y₅ and Mg₃Zn₃Y₂ compounds within the grain interiors, while the long-period phases remained stable in the cast-bulk alloy even at temperatures higher than 673 K.

A new technique has been developed for randomizing the basal plane texture formed by rolling or extruding deformation in a magnesium alloy. Specimens are roll-formed using rolls having wavy surfaces at elevated temperatures. This technique has been applied to specimens of AZ31B magnesium alloy sheet. The specimens were heated at 623 K and 723 K for 300 s, and then immediately wavy roll-formed. This process was repeated 8 times, rotating the specimen at 90 degrees for each subsequent pass. The specimen showed a typical basal plane texture before the wavy roll-forming, and the texture was randomized after the treatment. Annealing at 573 K and 673 K, and/or flat-rolling at 623 K on the wavy roll-formed specimen caused a reversion to the basal plane texture. Transmission electron microscopic observations on the wavy roll-formed specimen showed dislocation substructures consisting of many twins and dense dislocations, which resembled those formed by conventional flat-rolling. Randomizing would occur by macroscopic mechanism, such as lattice rotation due to wavy form deformation.

In order to improve the forgeability of a commercial wrought AZ31B magnesium alloy (Mg-3%Al-1%Zn) at room temperature, backward extrusion is carried out with applying counter pressure. A counter pressure is applied from a die exit of backward extrusion. By applying counter pressures of 100–200 MPa during backward extrusion, the critical punch stroke for fracturing is improved by 20% because the ductility increases under a high pressure. To predict the occurrence of fracturing of magnesium alloys, the distributions of the stress, strain and temperature during forging are calculated by the finite element simulation because the existing fracture criteria are not adequate to predict the occurrence of fracturing of magnesium alloys in forging. The mechanism of fracturing is discussed on the basis of plastic deformation, and a fracture criterion of magnesium alloy in cold forging is suggested. The newly proposed criterion provides much better results than the existing criteria.

In this paper, grain refinement of pure magnesium using severe plastic deformation was investigated in order to enhance mechanical properties of the hard-to-deform metallic material. The microstructure and the mechanical properties of Mg processed by equal channel angular pressing (ECAP) at various processing temperatures were examined experimentally. ECAP of channel angle of 90° and corner angle of 0° was successful without fracture of the magnesium workpiece at 300°C, but not under 200°C. The hardness of the ECAP processed magnesium decreased with increasing ECAP processing temperature. The effect of temperature on the hardness, instrumented indenting response and microstructure of the ECAP processed magnesium were discussed. Fracture behavior during ECAP under different processing temperatures was demonstrated using the finite element method associated with ductile fracture model.

The texture evolution of an as-extruded ZK60 Mg alloy with different tensile strains has been determined by X-ray diffraction technique. As strain increases, {0002} basal plane of most grains gradually inclines to the tensile direction, which is more pronounced for TD sample. This firmly suggests that the mechanical anisotropy and the difference of deformation modes between ED and TD samples are not only caused by initial basal texture, but also by the developed texture during the tensile test.

AZ31 and AZ61 Mg alloys were multi directionally forged (MDFed) during decreasing temperature from 623 K to 423 K to cumulative strain of ΣΔε=4.8 by Δε=0.8 pass strain at a strain rate of 3×10⁻³ s⁻¹. In both Mg alloys, the average grain size gradually decreased with increasing cumulative strain. After straining to ΣΔε=3.2, i.e., after 4 passes of MDF, ultra fine grained (UFG) microstructures with average grain size of 1 μm were uniformly evolved. By prolonged straining, the grains became further finer. The AZ61 Mg alloy MDFed to ΣΔε=4.0 showed quite high hardness over 1.2 GPa, while that of the AZ31 Mg alloy was 850 MPa at ΣΔε=4.8. The differences of UFG evolution and mechanical behaviors during MDF of AZ 31 and AZ61 Mg alloys are precisely investigated.

The effects of cyclic extrusion and compression (CEC) processing on the microstructure and mechanical properties of ZK60 Mg alloy were investigated at room temperature. ZK60 alloy was dramatically refined by CEC processing at 350°C. In addition, the initial fiber texture became disintegrated and changed into a {10\\bar13}⟨30\\bar32⟩+{10\\bar11}⟨1\\bar543⟩ texture. Due to microstructure refining and texture variation, the compressive yield stress of ZK60 alloy increased remarkably while the tensile yield stress decreased slightly. As a result, the intensity of strength-differential effect (SDE) of ZK60 alloy was decreased noticeably. The ductility of ZK60 alloy also enhanced, especially under compression test condition.

The as-cast microstructure of Mg-5Al-3Ca-xNd alloys consists of equiaxed α-Mg matrix, (Mg, Al)₂Ca eutectic phase and Al-Nd rich intermetallic compounds. With the increase of Nd addition, α-Mg matrix morphology was changed from dendritic to equiaxed grains due to suppression of grain growth by formation of homogeneous intermetallic compounds containing Nd dispersed at grain boundary and α-Mg matrix. And the grain size of as-cast alloys was decreased as addition of Nd was increased. This eutectic phase of the extruded alloys was elongated to extrusion direction and size of this phase was redined comparing to that of as-cast alloys because of severe deformation during hot extrusion. Maximum yield and ultimate tensile strength value of the as-extruded alloys was 322 and 335 MPa at Mg-5Al-3Ca-2Nd alloy, respectively.

Compression tests were conducted at the temperature of 573 K with the true strain rates of 10⁻³–1 s⁻¹ on as-cast and homogenized Mg-6Al-2Ca-2RE (RE = rare earth) (in mass%) alloy specimens, and their dynamic recrystallization (DRX) behaviors were investigated. Strain hardening occurred after yielding, followed by strain softening. The flow stress of the as-cast specimen was higher than that of the homogenized specimen. The DRX grain size depended minimally on the Z-parameter in both of the as-cast and homogenized specimens. This is likely to be due to the particle-stimulated nucleation mechanism involving the second-phase particles. When the specimens were deformed to the true compressive strain of 1.6, non-recrystallized regions were not observed in the homogenized specimen; however, they were partially observed in the as-cast specimen. The grain size in the recrystallized region in the as-cast specimen was smaller than that in the homogenized specimen. Elemental analyses revealed Al segregation around the second-phase particles in the as-cast specimen. Therefore, it is suggested that DRX in the present Mg-Al-Ca-RE alloy is affected by not only the second-phase particles, but also the Al segregation.

There are many techniques to deposit alumina film; most of these methods required special environment such as electrochemical deposition or complicated apparatus such as plasma spraying. In the present paper, anodizing of AZ31 in NaOH solution with co-precipitation of nano-size alumina particles was investigated to produce alumina-rich surface film on AZ31 magnesium alloy. The corrosion resistance was studied by potentiodynamic polarization technique; the corrosion resistance of AZ31 magnesium alloy was significantly improved by anodizing.

Two techniques for improving corrosion resistance in magnesium alloys were combined, coating with high purity magnesium and treating with fluoride. The specimens used were commercial AZ31B alloy. A vapor deposition technique was applied for the coating. Temperatures of an evaporation source were varied in the range of 823 to 973 K, while a temperature of the substrate, the specimen, was kept at 523 K. Then the specimen was immersed into molten NaBF₄ kept at 693 K for various durations. The corrosion resistance of the specimen was evaluated by immersion testing using a 0.02N HCl solution and also by salt spray tests. Fluoride-treated specimens coated with high purity magnesium showed superior corrosion resistance, even in the acidic solution. The fluoride films formed on the substrate were extracted and observed with a TEM. The films were composed of small grains about 0.5 to 1 μm in diameter, and no defects, voids, cleavages, or cracks were observed. Most of the diffraction patterns were indexed as an MgF₂ phase, although the fluoride layer is composed of MgF₂ and NaMgF₃ layers.

Diffusion pack coatings via Al-Si powders with an AlCl₃ chloride activator have been investigated in order to examine the surface protection effect on pure magnesium and magnesium alloys. Pure Magnesium and commercial AZ31 magnesium alloys have been subjected to diffusion coatings in an Al alloy powder for various time frames. When the pack coating was carried out at 823 K for 15 h, the Mg₁₇Al₁₂ layer has been successfully synthesized on the pure magnesium substrate. Similarly, a pack annealing at 823 K for 15 h showed a synthesized Mg-Al layer on the AZ31 magnesium alloy as a coating layer. Mechanisms for the surface layer formation are discussed together with growth kinetics and microstructural observations.

The stress corrosion cracking (SCC) behavior of an as-cast AZ91 magnesium alloy in 0.1 kmol/m³ Na₂SO₄ solution was investigated using slow strain rate test (SSRT). The results showed that both the uncharged and charged AZ91 alloy occurred transgranular stress corrosion cracking (TGSCC), which were characteristic of large-plane cleavage fracture. Pre-charging had little influences on mechanical properties. It indicated that hydrogen embrittlement (HE) was the main mechanism for the SCC of AZ91 alloy in 0.1 kmol/m³ Na₂SO₄ solution.

Corrosion resistance of anodized surfaces on high-purity magnesium (99.95 mass%), rolled sheets of ASTM AZ31B (Mg-2.9Al-0.85Zn) magnesium alloy and die-cast plates of ASTM AZ91D (Mg-9.1Al-0.75Zn) magnesium alloy has been studied. Anodization was conducted by environment-friendly electrolysis whose electrolyte consists of phosphate and ammonium salt. The anodized surface was covered with amorphous film, and showed only discoloration during salt spray test where formation of corrosion product (magnesium hydroxide) was well suppressed within 605 ks. Even when the anodized surfaces were trenched with ceramic knife to form locally exposed substrate, corrosion was well suppressed by formation of new type of dense protective films for each substrate which consist of oxygen, magnesium, aluminum and phosphorus. Anodic polarization curves indicate that the anodized surfaces show sacrificial function due to the thermodynamically unstable state of phosphorus in the anodized layers and its resulting release of electrons. From the viewpoint of kinetics in corrosion on the anodzed surfaces, the curves show that the anodized layers dissolve quite slowly into the electrolyte compared with the case of the untreated substrates. The excellent corrosion protectivity obtained by the anodization is considered to be based on the formation of a dense protective film on the exposed area, as well as sacrificial function of the amorphous anodized layer.

Magnesium alloys are lightweight materials with high specific strength and have electromagnetic shielding characteristics. On the other hand, chromate is known as carcinogen and it leads a limited use of the conversion coating on magnesium. In recent years, adhesion technology is essential and widely used in producing electronic equipment and sporting goods from magnesium alloys. Adhesives can easily bind different materials. Adhesives may even inhibit the contact corrosion of magnesium, and we may expect adhesion to be used to effectively join different metals.
This paper describes and compared with the influence of various non-chromate conversion coatings on the bonding strength of magnesium and aluminum alloys.
In this study, specimens of AZ31B and A2017, A6022 were used. The adhesive cements used were epoxy and acrylic resin. The results of a pull-off test and tensile lap-shear strength test ware evaluated.
The Mg(OH)₂ coating on AZ31B and Boehmite on A6022 exhibited a higher tensile shear strength (16 MPa) with epoxy resin. In the acrylic resin, Mg(OH)₂ coating on AZ31B and Boehmite on A6022 had a tensile shear strength of 14 MPa.
It is obvious that these conversion coatings can be alternatives to chromate conversion coatings as surface treatment for adhesion of magnesium alloys and aluminum alloys.

Conversion coating by immersion in solution including Mg(NO₃)₂ and/or La(NO₃)₃ was applied to commercial Mg alloys: AZ31, AZ61, AZ91 and AM60. The formed layer was analyzed, and the corrosion resistance of the specimen against salt water was investigated. The influences of the coating conditions on the characteristics of the layer and on the corrosion behavior were discussed. A thin oxide layer was formed on the surface of the specimen by the conversion coating, and La was contained in the layer obtained in the solution including La(NO₃)₃. The corrosion resistance of Mg alloys wasn’t remarkably improved by the conversion coating using either Mg(NO₃)₂ solution or La(NO₃)₃ solution, while it was particularly bettered by the coating using the solution including both Mg(NO₃)₂ and La(NO₃)₃. The good corrosion resistance was obtained under the wide concentration ratio of La(NO₃)₃ to Mg(NO₃)₂, and the optimum coating conditions for each alloy was specified. The pretreatment, such as the alkaline degrease, the acid pickling and the surface activation, was effective for the uniform coating on large specimen.

The effects of Ga content on the electrochemical behavior of Mg-5 at%Hg alloys which contain a small amount of Ga was investigated by the measurement of polarization curves and galvanostatic test. The microstructure of the alloys and the surface of the specimens corroded in galvanostatic test were observed by using scanning electron microscopy, energy spectrum analysis and X-ray diffraction analysis. It can be concluded that with the content of Ga increasing, the alloys come into Mg-Mg₃Hg, Mg-Mg_7.2(Hg, Ga)_2.8 and Mg-Mg₅Ga₂ binary phase fields sequentially. The best electrochemical activity occur in the Mg-5 at%Hg-1 at%Ga alloy, with open circle potential −2.124 V and mean potential −1.992 V. The corrosion resistance of the alloys is in the sequential order from big to small: Mg-5 at%Hg-5 at%Ga, Mg-5 at%Hg-22 at%Ga, Mg-5 at%Hg-1 at%Ga, Mg-5 at%Hg. The lowest corrosion current density is 0.418 mA·cm⁻². The activation mechanism of the magnesium alloy produced by Hg and Ga was concluded: the dissolution of Hg and Ga atoms leads to the back accumulation of liquid Hg and Ga, which makes a true metallic contact with a-Mg. Magnesium atoms diffuse through the liquid mercury and gallium to form magnesium amalgam and undergo severe oxidation at the amalgam/electrolyte interface. The reaction produces pure Hg and Ga again which continue the activation process.

This study was carried out to examine reduction mechanism of CaO and to investigate behaviors of CaO in pure Mg in terms of microstructure, oxidation resistance and phase formation. Pure Mg was used instead of Mg alloys to minimize the effects of other elements. With respect to CaO content, microstructures of the alloys showed prominent grain refinement. Mg₂Ca phase was formed even in 0.07CaO added pure Mg by reduction, while Mg₂Ca phase was formed over 1.35Ca added pure Mg. With respect to CaO content, the hardness of CaO added pure Mg was increased by grain refinement. From oxidation test by TGA, the oxidation behavior of CaO added Mg was similar to that of Ca added Mg. From AES result, there was the thin oxide layer mixed with MgO and CaO in CaO added Mg.

Magnesium alloys of AZ91D, AZ91D + (1, 3, 5) mass% Ca, and AZ91D + (0.5, 1) mass% CaO were cast and oxidized at high temperature in atmospheric air in order to study the effect of Ca and CaO on the oxidation. The microstructure of the CaO-added alloys was similar to that of the Ca-added alloys. Ca and CaO both formed Al₂Ca in the alloys, but Ca was more effective than CaO in increasing the oxidation resistance of Mg alloys. The microstructure and composition of the scale formed on the CaO-added alloys were similar with those on the Ca-added alloys.

Due to its light weight and abundance as a resource, the utilization of magnesium is increasing. AZ91 alloy is the most common cast magnesium alloy and is widely used as die-casting material. AZ91 is also used for sand mold casting. In sand mold casting, reaction with mold sand is expected because magnesium is a very reactive element. This study investigated the surface condition of AZ91 castings using sand mold.
Higher pouring temperature promoted the reaction with silica sand, and the surface of castings became rough. Reacting with mold sand, Mg₂Si and Mg and Al complex oxides were precipitated near the casting surface.

Deformation characteristics of a recycled AZ91 Mg alloy, obtained from machined chips by solid state recycling, were investigated by conducting tensile tests between room temperature and 773 K in the strain rate range of 3.3×10⁻²–3.3×10⁻⁴ s⁻¹. Tensile properties of the recycled specimen were compared with those of a reference specimen. The elongation to failure of the recycled specimen was lower than that of the reference specimen, except at room temperature and 753 K with 3.3×10⁻⁴ s⁻¹. The recycled specimen contained oxide contaminants whose size was −2 μm. Such oxide contaminants were responsible for the reduction in elongation to failure. The cavity formation due to the oxide contaminants was analyzed using existing theoretical models, and experimental results were compared with analytical results.

Recently, magnesium alloys have been considered as a promising alternative for high-strength steel and aluminum in some applications because of its advantages such as low density, high specific strength etc. However, the application of formed magnesium wrought alloys components is restricted due to lack of knowledge for processing magnesium alloys at elevated temperatures. In this study, the deformation behavior of a cylindrical deep drawing of magnesium alloy sheets at elevated temperatures are simulated by using a non-isothermal finite element based on DEFORM 3D commercial software. In order to validate the finite element analysis, deep drawing test of cylindrical cup of AZ31 and AZ52 rolled sheets at given conditions was also performed. The experimental results show a good agreement with the finite element simulation predictions. The optimal forming temperature, thickness distribution of the cup and punch force were determined for the process.

Improvement of deformability for Mg-based composite materials with a dispersion of Ti particles has been considered in terms of the strain transfer through the interface, but is not fully understood during the deformation of ductile Ti particles. Mg-based composites composed of pure Mg and pure Ti plates was investigated to clarify the strain transfer through the Mg/Ti interface using crystallographic orientation analysis based on electron back-scattered diffraction (EBSD) patterns. It is suggested that the larger Schmid factor and lower residual strain energy (W) are significant for the operation of a prismatic slip system in the Ti grains.

A warm/hot formability testing apparatus was designed and fabricated for this study. The forming limit curve (FLC) and springback characteristics of AZ31B Mg alloy sheets at elevated temperatures of up to 300°C were investigated. The forming limit increased rapidly with temperature up to 200°C, and increased slightly thereafter. In the range from 200 to 300°C, the FLC₀ was found to be six to seven times higher than at room temperature. In isothermal springback tests, the effect of the blank holding force (BHF) on springback differed slightly from that for other metal sheets at low temperatures. At 200°C and above, negligible springback was observed over the range of BHF’s used. With increasing temperatures, springback decreased rapidly up to 200°C, and very slowly afterward. In nonisothermal tests, considerable springback was observed, even at temperatures of 200°C or higher; furthermore, it decreased almost linearly with increases in both the temperature and BHF.

Due to their low density, high specific strength, and electromagnetic interference shielding, magnesium alloy sheets are increasingly used in automotive and electronics industries. However, magnesium alloy sheets are usually formed at an elevated temperature due to poor formability at room temperature. For the industrial use of magnesium alloy sheets, the mechanical properties at elevated temperatures and appropriate forming process conditions need to be developed. In this study, the warm deep drawing process of AZ31 sheets is numerically studied by non-isothermal simulation. The difference between the isothermal and non-isothermal simulation results and the progress of warm forming is also discussed. The drawn depth and thickness distribution obtained from non-isothermal simulation agreed well with experimental results.

In this study, simultaneous control of shape and hardness of AZ31 magnesium alloy sheets by incremental forming process was proposed. Influences of working temperature, giving strain and heat treatment temperature on hardness were investigated. AZ31 magnesium alloy sheets were formed into pyramidal shape by incremental forming process at 100°C and 200°C. Major strains given to the pyramidal faces were 0.1, 0.2 and 0.3. After forming, heat treatment was carried out at various temperatures. Combination of final shape and total equivalent plastic strain were changed by multi-step forming and hardness distribution was measured. From the experimental results, it was found that when heat treatment was done at 200°C for 10 min after forming at 200°C, hardness of the specimen became higher than that of as received one. When heat treatment was carried out at 175°C for 60 min after forming at 100°C, hardness of the specimen also increased. In the case of multi-step forming, strain was accumulated at forming temperature of 100°C and hardness increased, but not at the forming temperature of 200°C. By multi-step forming at 100°C, asymmetric hardness distribution with symmetric shape was realized and simultaneous control of shape and hardness was succeeded.

Microstructures and mechanical properties of dissimilar welding joint between Al alloy and Mg alloy by Friction Stir Welding (FSW) were investigated in comparison with laser welding of the same combination. Dissimilar joint of Al and Mg alloy by laser welding was very brittle because of building up Mg₁₇Al₁₂ inter metallic compounds in fusion zone. On the other hand, FSW is anticipated to welding dissimilar alloys with enough joint strength because it is a solid-state process without melting. In this paper, FSW was carried out to make dissimilar butt joints of Al alloy and AZ31 magnesium alloy with various tool rotational speed and welding speed. These joints showed higher hardness in their stir zones than that of parent AZ31 alloy because of Mg-Al inter metallic compound formation. However, the hardness of stir zone was lower than that of fusion zone of laser welding, and was changed with the welding parameters of tool rotational speed and welding speed (i.e. heat input ratio of FSW). The optimum welding conditions of Mg and Al dissimilar FSW joint and the influence of inter metallic compound distribution with mixing of materials in stir zone were discussed.

Magnesium and its alloys are very attractive for light weight applications. However, their use is complicated by the fact that dissimilar metals are joined by fusion welding. In the present study, the ability of shot peening to enhance butt joining of a magnesium alloy sheet with dissimilar material sheets was investigated. Shot peening improves the performance of the engineering components. In this process the substrate undergoes a large plastic deformation near its surface when hit by many shots. The substrate material close to the surface flows during shot peening. This plastic flow is characterized by a shear droop at the edge of the substrate, namely, the peened material overflows at the edge. When the dissimilar metal sheets with notched edges are connected without a level difference and then the connection is shot-peened, the sheets can be joined by the plastic flow generated by the large plastic deformation during shot peening. In this experiment, an air shot peening machine was used. The influences of air pressure and peening time on the joinability were examined. The joint strength increased with peening time, i.e., the amount of plastic flow. It was found that the present method can be used to enhance the butt joining of a magnesium alloy sheet with a dissimilar material sheet.

Monolayer friction surfacing was performed using a numerical controlled full automatic friction welding machine for AZ31 magnesium alloy plate used for substrate and AZ91 magnesium alloy casting bar used for consumable rod. Effect of the surfacing conditions on structures and mechanical properties of deposit were investigated. It was clearly observed that the circular pattern appeared on the surface of deposit by the rotation of coating rod. Microstructures of deposit showed finer structure than that of both base metals, and the cast structure was disappeared. Hardness of the deposit showed higher value than that of the substrate. Wear resistance of the deposit was improved in comparison with the substrate.

The joining of wrought magnesium alloy AZ31 and commercially pure aluminum A1100 plates was performed using explosive welding technique. Several welds were made by changing the experimental parameters. Optical microscopy and scanning electron microscopy were employed to observe the morphological and microstructural variations at the interface boundary. The geometry of the interfacial profile varied from smooth to rippled form with increase in the level of kinetic energy delivered to the bonding zone. The microstructure at the boundary was free of porosity and showed unique diffusionless dissimilar bonding. Localized zones of solidified melt in some cases were observed in the vicinity of the bonding line of the wavy-interfaced welds. Elemental analysis revealed the complex intermixed microstructure of these regions, accompanying with compositional variation due to formation of the metastable intermetallic phase Al₂Mg. The bonding strength of the welds, evaluated through shear tests, confirmed the high quality of the joints produced. Based on the experimental results the lower limit of the welding parameters which ensure achieving a satisfactory joint is proposed.

Rotating bending tests were performed at room temperature on the non-combustible magnesium alloy AMCa602, which was produced by adding 2% calcium (Ca) to the AM60 magnesium alloy. The fatigue strength at 10⁷ cycles was approximately 100 MPa. The fatigue property was strongly dependent on the inclusion size. In order to identify the type of the inclusion at the crack initiation site, elemental analyses were conducted by an electron probe microanalyzer (EPMA). The inclusion at the crack initiation site was AlN, which may have originated from impurities mixed in during casting. The relation between da/dN and ΔK was analyzed by the crack propagation behavior, and the fatigue life was evaluated by using the Paris law. As a result, it was clarified that most of the fatigue life was spent on crack initiation and micro crack propagation.

The effects of the grain size on the fatigue fracture behaviors in extruded AZ31B alloys were investigated. The mean grain sizes are 4.7 μm in F-specimen, 15 μm in M-specimen and 23 μm in C-specimen, respectively. The fatigue tests with R=−1 were carried out with a plane fatigue bending machine, which was originally developed for thin sheet specimen. S-N curves show that the fatigue limit of the F-, the M- and the C-specimens were estimated as 160 MPa, 150 MPa and 150 MPa, respectively. The F-specimen had the highest fatigue limit in the present alloys. On the other hand, the fatigue life in low cycle region of the F-specimen is shorter than those of the M- and C-specimens. Striation-like-patterns were observed on the fracture surfaces in all of the specimens, although the grain sizes were different. Twin was not observed in the F-specimen, but it was near the crack in the C-specimen. Consequently, twinning under the fatigue test depends on the grain size, and it affects the fatigue life of AZ31B alloys.

The authors previously proposed a two-step cold extrusion method for shaping spur gears. This method was applied to shape helical gears in this study. A specially designed die was used for shaping helical gears in two steps. The specifications of the gears examined were as follows: module m=1.5, number of teeth Z=18, helix angle β=20°. The material used for the experiment was low-carbon S15C steel. Workpieces with different inner diameters were formed to examine the effect of a reduction in cross-sectional area. To examine the effect of reductions in area, extrusion was carried out in three ways: 1) using a mandrel whose diameter is equal to the inner diameter of the workpiece; 2) using a mandrel whose diameter is smaller than the inner diameter of the workpiece; and 3) using no mandrel. Helical gears with complete teeth were formed in almost all the shaping conditions examined, even when the reduction in area was as low as 7% and punch pressure was relatively low.