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Mg–23.5 wt%Ni–10 wt%Cu and Mg–23.5 wt%Ni–10 wt%La alloys were prepared by melt spinning and crystallization heat-treatment. The Mg–23.5Ni–10Cu alloy (5.18 wt%) after planetary ball milling has a higher hydrogen-storage capacity than the Mg–23.5Ni–10La alloy (4.98 wt%) at 573 K. The activated Mg–23.5Ni–10Cu alloy has a slightly lower hydriding rate in the beginning, but a higher hydriding rate after about 5 min than the activated Mg–23.5Ni–10La alloy at 573 K. The activated Mg–23.5Ni–10Cu alloy has a much higher dehydriding rate and a larger quantity of the decomposed hydrogen than the activated Mg–23.5Ni–10La alloy at 573 K.

The solidification behavior of AZ31 magnesium alloy plate during horizontal continuous casting (HCC) with constant velocity was analyzed by three-dimensional CFD simulation. At steady state, the temperature profile in the direction of width was slightly inhomogeneous due to wide width compared to thickness. The temperature profile in the direction of thickness was symmetrical although the temperature at lower part was slightly higher than that at upper part. The region of high temperature increased rapidly with increasing the withdrawal speed, and then the finishing point of solidification increased dramatically. The shape of temperature profile was similar regardless of melt temperature but the overall temperature of plate and the finishing point of solidification increased with increasing the melt temperature. The finishing point of solidification decreased reciprocally with the coefficient of heat transfer.

In this study, carbon addition affects the formation mechanism and morphology of Al8(Mn, Fe)5, which serves as a nucleation site for α-Mg, conclusively leading to grain refinement of Mn-containing Mg–Al alloys. However, the grain size was decreased on slightly by carbon addition in Mn-free Mg–Al alloys, where Al4C3 particles were observed in the eutectic region. Therefore, it is suggested that Mn is necessary for considerable grain refinement of Mg–Al alloys, and that Al8(Mn, Fe)5 is an effective nucleant in Mn-containing Mg–Al alloys.

The effects of non-flux purification on the mechanical properties, microstructure and fracture pattern of AZ31+xCa magnesium alloys have been studied. The results show that the purification process of ceramic foam filters incorporating gas bubbling process can improve obviously the ultimate tensile strength σb and elongation δ of AZ31 alloy. With 20ppi MgO filter incorporating gas bubbling treatment under Ar flow rate of 2 l/min and temperature of 730°C, the σb and δ of AZ31 can be improved from 144.6MPa and 5.21% to 180.8MPa and 9.06% by 25% and 73.9%, respectively. Addition of 0.13%Ca to magnesium can not only increase the strength but also improve the elongation. With the further increase of more than 0.13% Ca content, the strength and elongation decrease. The experimental results show that under low Ca content, filtration purification process can greatly improve the σb and δ of AZ31+xCa alloy. However, with the increase of Ca content, the filtration effects decrease. The effective sequence of different filters is as follows: 20ppi MgO>20ppi Al2O3>10ppi MgO>10ppi Al2O3.

The hydriding properties of Mg– x Ni ( x = 13.5, 23.5 and 33.5 wt%) alloys with different microstructures produced by various processing routes were evaluated in this study. The hydrogen storage capacity and kinetics of hydriding of Mg– x Ni alloys were strongly dependent on their microstructures. The capacity and kinetics of hydriding were larger and faster when the average size of the hydriding phase was smaller and the volume fraction of the phase boundary was larger.

The effect of Ca addition on the corrosion resistance of AZ31 magnesium alloys was evaluated by observation of microstructure and measurement of corrosion potential and average corrosion rate. The main mechanism of corrosion of AZ31+xCa (x ¼ 0� 5 mass%) alloys was galvanic-corrosion between � -Mg and second phase. But the propagation behavior of corrosion was different with Ca content. In the alloy containing below 0.7 mass%Ca, a micro-galvanic cell formed between matrix � -Mg and second phase formed semi-continuously at grain boundaries and the corrosion progressed in transgranular mode. The propagation of corrosion was retarded when the corrosion front met the second phase acted as corrosion barrier. But in the alloys containing above 1 mass%Ca, a micro-galvanic cell formed between eutectic � -Mg and discontinuous second phase in the eutectic region and the corrosion rapidly progressed along eutectic � -Mg formed continuously at grain boundaries because the discontinuous second phase could not prohibit the propagation of corrosion effectively.

Recently application of magnesium alloys is expanded rapidly over the whole industry, especially in automotive and electronic industries. Most of magnesium alloy parts are produced by casting process and the quality control of castings is very important to reliability and durability of parts. Various properties of magnesium alloy castings are deteriorated by defects such as non-metallic inclusion and pore. 1–5) Especially control of non-metallic inclusion remained in magnesium alloy castings is very important because the possibility of entrance of non-metallic inclusion into melt is very high due to high reactivity of magnesium alloy melt with gas species above melt surface. There are various methods for removal of inclusions in melt including addition of flux, gas bubbling and filtration. 6–8) Formerly a method of addition of flux was mainly applied to remove inclusions from magnesium alloy melt. 9–11) But part of flux was entered into melt during pouring when flux could not be entirely removed as dross and/or sludge before pouring and the flux remained in casting degraded the quality of castings as harmful defect. So a method of bubbling of inert gas into melt has been paid attention as new method for removal of inclusions from melt, especially during steelmaking. 12–15) But studies on removal of inclusions from magnesium alloy melt by gas bubbling have not been carried out actively. In this study the effect of Ar gas bubbling on the removal of inclusions from AZ91D magnesium alloy melt is evaluated indirectly by measurement of tensile elongation of gravity mold castings of AZ91D magnesium alloy and analyzed qualitatively.

It is well known that ignition temperature increases dramatically through combined addition of Ca and Y to AZ series Mg alloys. Therefore, the industrial application of Mg alloys is expected to be expanded gradually. However, studies on corrosion behavior of these alloys have been carried out rarely even though the evaluation and understanding of corrosion behavior are necessary for wide application. In this study, the changes of microstructure and corrosion behavior of AZ series alloys according to the content of Ca and Y were systemically evaluated by immersion and salt spray tests. The corrosion resistance of AZ series alloys was improved dramatically by combined addition of Ca and Y without degradation of mechanical properties. It implies that the AZ series alloys containing optimized amounts of Ca and Y have the excellent combination of ignition resistance, corrosion resistance and mechanical properties.

Magnesium plate of 120 mm width and 30 mm thickness was produced by horizontal continuous casting, and its microstructures were analyzed on the surface and in the plate interior. The defect formation on the surface and subsurface, such as side cracks, buckling, pores and segregation, was very sensitive to the casting condition and processing parameters. Especially, a secondary cooling was effective in refining the microstructure and controlling the grain size distribution across the plate thickness, which means that the cooling rate and curvature of the solid/liquid interface in the mold changed. According to AES analysis on the surface, the thickness of the oxide layer was not more than 0.3 μm. However, the cyclic marks on the surface were obvious, because the plate were drawn by four-step cycle. In the case of several defects, they caused side cracks during rolling and survived even after rolling. Thus, it was concluded that pretreatment of the as-cast plate, such as homogenization and surface machining, is necessary to produce sound thin sheet by hot rolling.

Most failures of ductile materials in metal forming processes occurred due to material damage evolution - void nucleation, growth and coalescence. In this paper, the modified yield function of Liao et al in conjunction with the Hosford`s yield criterion is studied to clarify the plastic deformation characteristic of voided anisotropic sheet metals. The void growth of an anisotropic sheet under biaxial tensile loading and damage effect of void growth on forming limits of sheet metals are investigated. Also the characteristic length defining the neck geometry is introduced in M-K model to incorporate the effect of triaxial stress in necked region on forming limits. The forming limits theoretically predicted are compared with experimental data. Satisfactory agreement was obtained between the predictions and experimental data.

In the present study, tensile behavior of friction-stir-welded AZ31 (Mg-3.6Al-1Zn-0.6Mn in wt pct)-H24 Mg alloy was investigated. It was found that the tensile property, particularly tensile elongation, of AZ31-H24 alloy was significantly degraded with friction stir welding (FSW). The tensile fracture always occurred at the boundary between the thermomechanically affected zone (TMAZ) and the stir zone (SZ) on the advancing side. The fractographic examination on the tensile-fractured AZ31-H24 alloy specimen showed a mixed mode of cleavage and dimpled rupture. The AES analysis suggested that the significant reduction in tensile elongation of friction-stir-welded AZ31-H24 Mg alloy was attributable to the entrapped oxides along the boundary between the TMAZ and SZ.

The effects of Ni content on the microstructures of gravity cast Mg−Ni alloys were examined. Different shapes of primary solid particles and microstructures of the eutectic matrix were observed with varying Ni content. The eutectic matrix in the hypoeutectic alloy consisted of rod-like Mg2Ni phase with a small amount of α-Mg phase. The eutectic matrix in the near-eutectic and hypereutectic alloys consisted of eutectic cells oriented in different directions. A transition of lamellae to fiber occurred. The formation of cellular structure and transition of lamellae to fiber resulted from two-phase instability in the coupled region induced by constitutional undercooling.

In this study, the effects of Ca content and processing variables on the external surfaces and tensile properties of hot-rolled AZ31-xCa sheets were evaluated systematically. The number and length of side crack were decreased with increasing preheating temperature and decreasing reduction ratio per pass and Ca content. The UTS and YS were not strongly dependent on the Ca content but the elongation decrease with increasing Ca content. The amount of decrease in elongation due to increase in Ca content was least when the sheets were fabricated under preheating temperature of 400 � C and reduction ratio per pass of 15%. The sheets had the sound external features with little side cracks by homogenization of gravity cast AZ31-xCa alloys before hot rolling. In the cases of AZ31-xCa alloys containing under 1 mass% Ca, the annealed sheets after homogenization and hot rolling had the similar tensile properties to those of AZ31 sheet.

Semi-solid processing is an emerging technology for near net-shape production of engineering components. Although there has been significant progress in semi-solid processing of Al alloys, very limited information is available on semi-solid processing of Mg alloys, except for the thixomolding process. In semi-solid casting process, it is necessary to properly control the flow and solidification behavior of semi-solid slurries for high quality products. There are a number of parameters that affect the flow and solidification behavior of semi-solid slurries such as viscosity, casting pressure, shapes of gate and mold cavity, gate velocity, mold temperature, etc. In the present study, the effects of various thermo-mechanical treatments were investigated on the change in viscosity of the semi-solid AZ91D magnesium alloys by using a concentric cylinder type viscometer. The effects of gate velocity and thickness on mold filling behavior of the semi-solid AZ91D alloys were also investigated by using a high-speed camera and the results were compared with those obtained from computer simulations. From these results and microstructure examination, a processing map for high pressure die casting of the semi-solid AZ91D alloy was constructed in order to produce sound castings.

The effect of Sn:Zn ratio on corrosion behavior of magnesium alloys containing Sn and Zn was evaluated systematically by potentiodynamic polarization and immersion tests. The hydrogen evolution rate during cathodic polarization and the average corrosion rate measured by immersion test increased with increasing Sn content and Sn:Zn ratio. The changes of fraction of second phase with more positive corrosion potential and solute contents in the matrix phase were responsible for the change of corrosion behavior according to Sn content and Sn:Zn ratio. Mg2Sn particle accelerated the corrosion by formation of micro-galvanic cell, which resulted in faster corrosion rates of Mg-5Sn-xZn alloys than those of Mg-2Sn-xZn alloys. The increase of Zn in the matrix was harmful to the corrosion resistance because Zn accelerated the hydrogen evolution although ZnO was beneficial to the passivity of surface film.

The microstructures and corrosion behaviors of the magnesium alloys containing Sn and Zn are evaluated systematically. The as-extruded TZ alloys show a typical equi-axed grain structures formed by dynamic recrystallization. The fine particles of Mg2Sn phase are observed in grain interior and along grain boundaries. The corrosion potential measured by potentiodynamic test increases with increase of Zn content. The current density at cathodic region increases with increase of Zn content, which means that the hydrogen evolution rate increases with increase of Zn content. It seems that the corrosion behaviors of as-extruded TZ alloys will be affected by the amount of Sn and Zn dissolved into the α-Mg phase and the fraction of Mg2Sn phase.

This paper suggests a novel method for improving the ductility of magnesium alloy sheets using a laser scanning treatment combined with a defocusing technique. The crystallographic orientation on both surface regions of the AZ31B magnesium alloy sheet processed using this method was changed from a strong basal texture to an almost random texture. The laser-scanned magnesium alloy sheet showed enhanced tensile elongation of up to 50% with a similar a tensile strength.

The combined addition of calcium and yttrium lead to significant increase in non-flammability and tensile properties, compared to conventional Ca-containing magnesium alloys. It means that we can reduce the amount of calcium addition to get certain amount of non-flammability in the alloys containing both calcium and yttrium together. Because the addition of calcium only can increase the ignition temperature but decrease the tensile properties, it should be minimize not to decrease the tensile properties. Corrosion behavior of calcium and yttrium containing alloys were also investigated systematically, and show that they have better corrosion resistance than the any other commercial alloys or calcium containing alloys. Detailed study on the corrosion behavior confirms that there are optimum amount of calcium and yttrium addition to get best corrosion resistance, and corrosion behavior of these alloys are quite different with other alloys.

Grain refinement involving inoculation of a grain refiner was investigated for application to a commercial Mg alloy. Cylindrical pellets composed of a mixture of MnCO3 and carbon powder with several different ratios were plunged into a commercial AZ91 alloy. The results show that the addition of the mixed pellets can more efficiently refine AZ91 compared to the individual use of carbon powder or MnCO3. In particular, the addition of mixed pellets with a 3:7 ratio between MnCO3 and carbon provides an excellent refining efficiency, decreasing grain size from 460µm to 52µm of the AZ91 alloy. This is attributed to inoculation of MnCO3 and carbon, which brings about the formation of heterogeneous nucleants such as MgO, Al4C3, and Al8Mn5 before solidification of a-Mg and also to melt agitation by the release of CO2 gas