Abstract: The effects of homogenization treatment on the electrochemical corrosion behavior of Mg-0.8wt%Ga-0.8wt%In anode materials were investigated by the polarization and galvanostatic curves tests. The scanning electron micrographs of the secondary phase after heat treatment and the corroded surface of the specimens were observed. The corrosion product of the Mg-0.8wt%Ga-0.8wt%In alloy was determined by X-ray diffraction. The results show that the intergranular compound dissolved in the Mg matrix in the Mg-0.8wt%Ga-0.8wt%In after homogenizing at 673K for 24h. The least corrosion current density, 0.029mA/cm2, appeared in this specimen due to the least corrosion driving force. The corrosion of the Mg-0.8wt%Ga-0.8wt%In alloy in a 3.5% NaCl solution was generous corrosion and pitting attack. The corrosion product has been found to be mainly Mg (OH)2.
Abstract: In order to develop ignition resistant magnesium alloy, Ca and Ce elements were selected alloying elements to fabricate Mg alloy. Different content of Ce (0,0.5,0.8,1.2,1.5wt%) and Ca (0, 0.6,0.8,1.0wt%) were added into pure magnesium to analyze their ignition-proof effect. The concentration of Ce and Ca elements on the melt surface was believed to be key factor for ignition resistance, which caused the change of interfacial tensions. It was indicated that the ignition resistance could be improved with increase of Ce and Ca addition. This could be attributed to a protective surface oxide owing to the diffuse of Ce and Ca to surface.
Abstract: Automobile wheel hub of Mg alloy with single-step extrusion-forging process was developed, and the microstructure and mechanical properties after heat treatment were investigated. The forged hubs have a hub wall of as thin as 3mm, and 4-7kg lighter than that of Al alloy wheel hub with a same size and design of each wheel hub, that would lead remarkable reduction of fuel consumption. The tensile strength larger than 308 MPa, good corrosion fatigue and impacting resistance sampled from the hubs obtained.
Abstract: The high strength of Mg-Y-Nd alloy has been achieved primarily by precipitation hardening. Therefore, it is important to investigate the influence of various precipitate phases on the tensile properties of Mg-Y-Nd alloys. In this study, an extruded Mg-Y-Nd alloy was aged at various temperatures to examine the hardening behaviors. The results showed that the as-extruded alloy exhibited remarkable age hardening response at 210°C due to the precipitation of β’, and slight hardening response at 150°C and 280°C due to the precipitation of β’’ and β, respectively. Furthermore, different precipitates exerted different effects on the tensile properties. In comparison with the as-extruded alloy, the yield strength of the alloys aged at 210 °C and 150 °C was increased by 21 MPa and 8 MPa, respectively, whereas the yield strength of the alloy aged at 280°C was decreased by 30 MPa. The elongation of the alloy aged at 210°C and 150°C was also largely reduced by 3.4% and 2.9%, respectively, while the elongation of the alloy aged at 280°C was only slightly reduced (6.3%). Moreover, compared with the as-extruded alloy, the alloy aged at 210°C and 150°C exhibited lower hardening capacity and higher strain hardening rate at the initial stage, but the strain hardening rate decreased more quickly with the increasing stress. The alloy aged at 280°C exhibited similar strain hardening behavior with the as-extruded alloy. The results in this study provide guidelines for determining the heat treatment parameters for the Mg-Y-Nd alloys to improve their tensile properties.
Abstract: Mg-2Zn-0.3Gd sheets processed by large strain hot rolling with one pass of 80% reduction at 200°C and 250°C were selected to investigate the rolling temperature effect on the microstructure, texture and mechanical properties of Mg-2Zn-0.3Gd sheets after rolling and subsequent annealing. It was found that the rolling temperatures in the present study seemed to have no obvious effect on the microstructure of Mg-2Zn-0.3Gd sheets during large strain hot rolling process. High density of shear bands and numerous intersected twins but free of DRX grains were observed in the microstructure of both sheets. The Mg-2Zn-0.3Gd sheets showed non-basal textures with peaks tilting to TD after annealing. While the peak intensity of (0002) pole figure increased as the rolling temperature decreasing. Tensile testing results revealed that the Mg-2Zn-0.3Gd sheets rolled at both temperature displayed high room temperature ductility about 40% after annealing, which is due to the existence of non-basal texture.
Abstract: In this paper, a new process for the production of the primary magnesium is introduced using the dolomite as the raw material. The magnesia and calcium carbonate were prepared from dolomite by acidification. The content of magnesium oxide can reach 98.92% about the magnesia obtained. The magnesia is used to produce primary magnesium by aluminothermic reduction under vacuum condition. The reduction ratio of MgO can be up to 86.14% under the temperature of 1200°C for 5hrs, briquetting pressure of 10MPa and the molar ratio of MgO to Al of 3:2. The content of magnesium is more than 99.90%. The major phases in the briquette residue are corundum and spinel, which can be used as refractory.
Abstract: Magnesium alloys are very active and readily ignite during heating and melting. In this study, the ignition-proof property of AZ91D with Nd and Dy addition was discussed, and the effects of these ignition-proof elements on the microstructure and microhardness of AZ91D investigated. The results show that the ignition-proof performance of magnesium alloy is improved obviously. The ignition resistance is attributed to the compact oxide films, which consist of MgO, Al2O3, Nd2O3, Dy2O3. When Dy content increased beyond 0.5%, the change tendency of ignition point of the alloy follows the shape of “v” curve, and the ignition point increased with Nd addition. The optimum composition of the newly developed magnesium alloy is AZ91D-3Nd-0.5Dy with the ignition point about 60K higher than AZ91D. And also AZ91D-3Nd-0.5Dy has fine microstructure and higher microhardness.
Abstract: The corrosion behavior of Mg-9Li-3Al-2.5Sr alloy, solution treated at 400°C for 3h with various aging temperature (Ta; Ta=75,100,125,150,175°C), was investigated in 3.5% NaCl solution by immersion test and polarization curve measurement. Experimental results suggest that the alloy aged at150°Cfor 6h exhibits the highest corrosion resistance while the alloy treated at 75°C for 6h presents lowermost corrosion resistance. The corrosion resistance of the alloy is related to the grain size and the distribution of Al4Sr compound. The segregation of intermetallic compounds can accelerate the corrosion process. It was found that duo to the proper solid-solution and aging treatment, intermetallic compounds were distributed evenly along the grain boundaries, which can reduce the corrosion rate and corrosion current. In addition,with the growth of grain, the decrease of the grain boundary area per unit volume lead to improvement of corrosion resistance of the alloys.
Abstract: The elevated temperature flow stress behavior of Mg-9Gd-2.5Y-1Nd-0.5Zr magnesium alloy was carried out by Gleeble-1500 thermal mechanical simulator in the temperature range of 460-520°C and in strain rates of 0.0005~1s-1 at a strain of 0.6. The optical microscopy was used for microstructure characterization. The results showed that the flow stress increases with increasing strain rates and decreasing temperature. All the deformed magnesium alloy specimens show a dynamic recovery characters in the temperature range from 460~500°C, and show dynamic recrystallization characters at 520°C. The flow stress of this alloy can be represented by Zener-Hollomon parameter function, and values of related parameters A, α and n, are 2.24×1013s-1、0.027MPa-1 and 2.93, respectively. Its activation energy for hot deformation Q is 212.6kJ/mol.