Materials Science Forum Vols. 488-489

Abstract: Ammonination technique for dehydration of hydrated magnesium chloride is a special kind of method for preparation of high-pure anhydrous magnesium chloride, which is requisite for electrolytically manufacturing metal magnesium. The technique has been developing for decades in the west world. China has now been exploiting the technique for his magnesium ore, especially the magnesium resource in the west of China. We started investigation of the method for several years, and several new progresses were arrived for preparation of anhydrous magnesium chloride. From our study, ethanol, methanol and water solution can be used for the method, and each had an advantage over the others; the ammonia used in the technique for preparation of anhydrous magnesium chloride is less corrosive for the equipment, and friendly for environment. The method gives great potential application in industry of metal magnesium and magnesium matrix materials.

Abstract: The deformation and recrystallization behavior of two magnesium alloys, AZ31 and WE43, have been investigated. The cast alloys were heat treated to produce various distributions of second phase particles and deformed in a channel die at a strain rate of 10-4 s-1 at temperatures between 523 and 673 K. The alloys were subsequently annealed at temperatures between 708 and 798 K.The AZ31 and WE43 were extruded at 555 and 633 K, respectively. The microstructures were compared to those developed during channel die deformation. The tensile and compressive strengths and the texture of the alloys were determined in the as-extruded and recrystallised conditions.Optical microscopy and electron backscattered diffraction (EBSD) were used to characterize the microstructures of the alloys. The EBSD technique was used to determine the texture of the deformed and annealed samples.

Abstract: The Mg-Zn-Zr alloy ZK60 with added trace rare-earth elements Y(0.9wt%) and Ce(0.9wt%) were prepared. After hot extrusion and aging treatment, the tensile mechanical properties of the alloys were tested at room temperature. Microstructures of the alloys were investigated by optical microscope (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The existing form, affecting mechanisms of trace Y and Ce in alloys and the effects on the microstructures and mechanical properties of ZK60 alloy were discussed. The results showed that: trace rare-earth elements Y and Ce both had remarkable grain-refining effects on the alloys, while the grain-refining effect of Y was more significant than that of Ce. RE elements Y and Ce improved the mechanical properties of the ZK60 alloy, but the strengthening effect of Y was more remarkable. It was found that σb of Mg-Zn-Zr-Y alloy was improved by 12.6％. Addition of Ce to the ZK60 alloy led to an increase in ductility of the alloy from 15% to 17%.

Abstract: Influences of Ca addition on microstructures and mechanical properties at room and elevated temperatures up to 300oC have been investigated for EZ43 (Mg-4%RE-3%Zn)-(0~1.2)%Ca permanent mould casting alloys, based on experimental results from optical micrography, X-ray diffractometry, scanning electron microscopy combined with energy dispersive X-ray spectroscopy and mechanical tests. With an increase in Ca content, yield strength is increased gradually at all temperatures, whereas elongation shows a decreasing tendency. High level of tensile strength around 150MPa is maintained until 250oC in the EZ43-0.8Ca and EZ43-1.2Ca alloys, meaning that Ca is very effective for improving elevated temperature strength of the Mg-RE-Zn alloy. The microstructural examinations reveal that Ca refines the a grains markedly, increases discontinuity of Mg12RE network intermetallic compound and dissolves into the Mg12RE phase. The refined a grains and Ca-containing Mg12RE with higher thermal stability are considered to be responsible for the improved mechanical properties at room and elevated temperatures for the EZ43-Ca alloys.

Abstract: By use of the Zwick electronic universal material testing machine, X-ray diffractometer, SEM, EDX, image analyzer and corrosion test, the effects of LaCl3 on the mechanical properties, structure, fractography and corrosion behavior of magnesium alloy have been studied. The results show that minute nodular Al10La2Mn7 phases can be formed in Mg melts after fluxes containing LaCl3 are added to Mg melt. The Al10La2Mn7 phases can act as the nucleating site of γ phases, and the γ phases can be refined. With the flux containing 5% LaCl3, the σb and δ of the Mg alloy can be improved from 161MPa and 2.1% to 203MPa and 4.0% by 26% and 100%, respectively. The corrosion rate of magnesium alloys can decrease from 1.10 mg/(cm2.d) to 0.17 mg/(cm2.d) by 84% with the use of flux containing 5% LaCl3. Rare earth (RE) elements are often added to the magnesium alloy to improve the alloy structure and the room or elevated temperature mechanical properties. But up to present, the RE elements added to Mg melt is often in the form of pure RE alloy or RE master alloy [1]. Because RE is the oxidizable material, this kind of adding process often leads to low RE utilization ratio and high use-cost. Besides, this process can easily induce segregation of RE and the appeared coarse RE phases will lower the Mg alloy mechanical properties. By far, there is few research reports about RE contained compound added to Mg alloy melt. In this paper, the effects of Lanthanum chloride (LaCl3) on the structure and mechanical properties of Mg alloy are studied for the first time. The aim is to explore a new way to improve the Mg alloy properties.

Abstract: In this study the effects of Ca addition on the rollability, microstructures and tensile properties of AZ31 alloy were evaluated. In Ca containing alloys, reduction ratio and preheating temperature are the most important variables to make good sheet without any crack. The number and length of side crack increased with increasing Ca content. With increasing the reduction ratio per pass and decreasing the preheating temperature, crack initiates easily at the side. The dendritic grains were changed to fine equiaxed grains through hot rolling by dynamic recrystallization. The Al2Ca precipitates which were segregated to grain boundaries during solidification were rearranged parallel to the rolling direction. The tensile properties of hot-rolled AZ31-xCa sheets were decreased slightly by addition of Ca.

Abstract: As-cast AM50 magnesium alloys containing 0, 1, 2 wt. %Ca were extruded firstly at 673K with an extrusion ratio 1:9, and then at 573K with an extrusion ratio 1:16. Microstructure, tensile properties and fractographs were investigated. With Ca content increasing, the amount of Al2Ca increases and that of Mg17Al12 decreases. Ca refines the microstructure of as-cast and extruded AM50 magnesium alloys. For the extruded magnesium alloys, tensile strength improved and elongation decreased at room temperature, while tensile strength was reduced a little and elongation reduced at the temperature of 100°C, 150°C and 200°C with increasing Ca content. The tearing face increases with Ca content increasing for the tensile fractographs.

Abstract: Mg92Zn6Y1.5Zr0.5 alloy was extruded at 300, 350, 400 ı. Then, the alloy was aged at 180 ı. The microstructure and mechanical properties of the extruded alloy and aged alloy were investigated. The precipitation behavior of aging process was investigated. The increase of yield strength at room temperature and ultimate strength at elevated temperature after the aging process has been ascribed to the strengthening effect of these precipitates.

Abstract: Mg-8Zn-4Al-xY base alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were prepared by casting into a copper mould at moderate cooling rates. The Y addition was effective for decreasing the size of i-phase and the more homogeneousness of its dispersed state. The mechanical properties at room temperature were much superior to those of AZ91 alloy. The creep tests indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg-Zn-Al-Y cast alloy. The dislocation characteristic in crept specimens which containing i-phase and no i-phase was analyzed and strengthening mechanism was discussed.

Abstract: The applications of ab initio calculations for deformation mechanisms of Mg-based alloys are discussed. First, Peierls stress of pure magnesium is calculated from generalized stacking fault (GSF) energies obtained by ab initio calculations. Second, materials design is applied to develop new Mg-based alloys exhibiting high strength. The atomic size factors of some Mg-based solid solutions are calculated by ab initio calculations as a first step of searching most effective solute element for the solid-solution strengthening.