Materials Science Forum Vols. 539-543

Abstract: The range of applications for magnesium alloys is still limited due to their relatively poor corrosion behavior. In recent years, various new magnesium alloys were developed, some of them with improved corrosion properties, thus opening new fields of application. However, the number of alloying elements for the use in conventional cast processes is limited due to their interaction with liquid magnesium, other alloying elements or large differences in the melting temperatures. The possibilities for grain refinement by post-processing are also restricted. PVD techniques can help to produce supersaturated precipitation free and microcrystalline magnesium layers. Using ion beam and magnetron sputtering, binary or ternary Mg-Al, Mg-Ti and Mg-Sn alloy systems as well as standard alloys (AM50, AZ91 and AE42) were deposited on silicon and on magnesium substrates. The effect of the microstructure on the corrosion properties was studied by comparing as cast material and PVD coatings using potentiodynamic polarization, linear polarization resistance, and electrochemical impedance techniques.

Abstract: Equal channel angular pressing (ECAP) was applied to commercial pure magnesium alloy, Mg-1wt%Si alloy and Mg-4.2wt%Zn-0.7wt%Y alloy. With increasing ECAP passes, both tensile strength and ductility of the alloys are increased, which are mainly resulted from the grain refinement. At the same time, for the Mg-Zn-Y alloy with inherent low damping capacity, damping capacity is increased after ECAP passes, however, the damping capacity is still low even after 6-pass ECAP. While for the commercial pure magnesium and Mg-Si alloy with inherent high damping capacity, although the damping capacity is decreased obviously after ECAP, Q-1 is still greater than 0.01. The damping capacity after ECAP processing is mainly influenced by grain size and deformation microstructure. ECAP paves a way for the development of magnesium alloys with high strength and high ductility combined with high damping capacity.

Abstract: AZ91D magnesium alloy was anodized in an electrolytic solution with phosphate as the main component. The conductivity and structure of the obtained coatings were examined. The anodic oxidation coatings are found to be composed of Mg, O, Al, and P. By controlling the phosphorus content, conductive coatings could be formed with surface resistivities of 0.2 ' or less. XRD analysis and TEM observations reveal that the structure of the conductive coatings is amorphous.

Abstract: The effects of Y addition to the Mg-Zn-Y-Zr alloy on the change of the microstructure and the mechanical properties (with the Y content range of 1 to 3 wt%) have been investigated. It shows that when Zn content is constant (5.65wt%), the alloys with Y content between 1.17 and 1.72wt% nearly reach its highest strength. With the composition near the optimums, the extruded Mg-6%Zn-1%Y-Zr alloy shows high strength and excellent ductility. The deformation behavior of this new alloy at high temperature has also been studied. Moreover, the super-long fatigue behavior of the Mg-6%Zn-1%Y-Zr alloy has also been tested, the results show the alloy with a high fatigue strength of about 85-90MPa in the super-long fatigue life regime of 1×109 cycles.

Abstract: Magnesium alloys have been known as the best lightweight metallic materials for various applications of electronic equipments and automobile parts due to high specific strength and stiffness. The needs for wrought magnesium alloys have been increased for the application to structural parts in the form of sheets and bars. However, magnesium has a hexagonal closed-packed (HCP) crystal structure with a limited number of operative slip systems at room temperature, and its formability is restricted to mild deformation. The improvement of the formability of magnesium sheets for real applications is important. In order to increase formability of magnesium sheets at elevated temperature, one promising way is a grain refinement.

Abstract: Uniaxial compression tests on hot-rolled AZ31 Mg alloy were carried out at 200°C. In order to investigate the evolution of texture during plastic deformation, cylindrical specimens were compressed to the rolling and normal directions. Experimental investigation reveals that work hardening and texture evolution are strongly dependent on the loading direction. The occurrence of deformation twinning was revealed by the observation of microtexture using electron backscatter diffraction (EBSD). A visco-plastic self-consistent (VPSC) polycrystal model was used to simulate the texture evolution during the uniaxial compression. The texture evolution induced by crystallographic slip and deformation twinning can be explained by the relative activity of each deformation modes.

Abstract: Magnesium (Mg) alloys are becoming one of the key engineering materials for aerospace and automotive industries because of their low density, high specific strength, excellent machinability and good diecastability, etc. In the meantime, conventional Mg alloys are limited for their low strength and creep resistance. Therefore, special attention is given on its applications at high temperature such as the transmission case and the engine block, In the near decades, much effort have been devoted to improving the properties such as strength, ductility, creep resistance of Mg alloys by adding rare earth (RE) elements, and it has been certified that the addition of RE do improve the performances of the Mg alloys. In this paper, we will review the progresses in the investigations of the Mg-RE alloys as a structural material, and also propose its application prospect in future.

Abstract: Samples of extruded magnesium alloy AZ31 (nominally 3 wt% Al, 1 wt% Zn, 0.3 wt% Mn, with the balance magnesium) were tested in uniaxial compression at temperatures from room temperature to 200°C. Monotonic and strain rate jump tests were conducted, and strain rate sensitivity, and activation volume were determined. At the lower temperatures tested, strain rate sensitivity was found to increase with strain to a limiting value, whereas at 200°C strain rate sensitivity initially followed a similar trend, but did not reach a limit within the bounds of the test. The effect of temperature on strain rate sensitivity was minor up to 150°C. Activation volume decreased with stress by roughly an order of magnitude over the course of the tests. An analytical model was modified to incorporate strain rate sensitivity, and it is shown that the evolution of material by twinning into an orientation favourable for slip is principally responsible for the trend in strain rate sensitivity with increasing strain.