Papers by Keyword: Magnesium Alloy

Abstract: Novel environment-friendly magnesium alloys have been developed by alkaline earth metal oxides addition without increasing cost and damaging process-ability. They can establish simultaneously ① cleaner processing routes with reduced or without SF6 gas, ② melt cleanliness in furnace and during transfer and pouring, ③ improved process abilities of casting, forming, welding and powder metallurgy such as fluidity, hot tearing susceptibility, inclusion and eutectic phase, ④ cost reduction with low-cost elements as well as by reducing or eliminating high-cost protective gas like SF6 gas, ⑤ original process abilities, ⑥ improved mechanical properties by grain refinement and internal soundness, ⑦ improved welding performance and joint properties, ⑧ safety during applications by improving oxidation and flame resistance and ⑨ improved remelting and recycling abilities. CaO, one of alkaline earth metal oxides, added Mg alloys can be well manufactured by conventional melting and casting without protective gas. This paper will discuss the effect of CaO on optimum protective gas usage, oxidation resistance and flame behavior of magnesium alloys.

Abstract: The perfect semi-solid magnesium alloy had been prepared using ultrasonic stirring method. The effect of technological parameters such as melt temperature, ultrasonic power and ultrasonic treatment time on the microstructure of semi-solid AZ61 alloy had been investigated. The results showed that the better refined and well-distributed globular semi-solid magnesium alloy had been acquired with the increasing of output power of ultrasonic stirring when melt temperature and ultrasonic treatment time were at a certain range.

Abstract: Magnesium alloys are becoming important material for light weight car body, due to their low specific density but high specific strength. However they have a poor weldability, caused by high oxidization tendency and low vapour temperature. In this study, the welding performance of magnesium alloy was investigated for automobile application. The material was rolled magnesium alloy sheet contains 3wt%Al, 1wt%Zn and Mg balance. The effects of filler wire addition was investigated on 2kW Nd:YAG laser welding. For the results, the mechanical properties of welded specimen were similar with base metal in laser welding with and without filler wire. The bridging ability was improved with filler wire without weld properties deterioration on laser welding of magnesium alloy.

Abstract: The aims of this study are to investigate the microstructure evolution of AZ31 Mg alloys with normal rolling and cross rolling as the large strain hot rolling affects microstructure, texture and mechanical properties of AZ31 Mg alloys. In the microstructures of as-rolled both samples, twins are clearly apparent, small and recrystallized grains are visible along some grain boundary and twinned regions. The Lankford values of large strain cross rolled sample obviously demonstrate the higher average r-value and lower planar anisotropy value. The press formability of cross rolled Mg alloy might be improved due to control of texture and grain size by severe deformation.

Abstract: A cellular automaton (CA) based model for two-dimensional simulation of the grain morphology of high pressure die casting magnesium alloy was developed. The heterogeneous nucleation, the solute redistribution both in liquid and solid, the interface curvature and the growth anisotropy during solidification were also considered in the model. By fitting the curve of grain density distribution, parameters of continuous nucleation equation based on Gaussian distribution were calculated. The microstructure simulation of step-shape die castings of AM50 magnesium alloy was studied. The metallographic microstructure of the castings at the surface and center of three steps with different initial die temperature was investigated. The simulation results were compared with the experimental results and they were in good agreement on average grain size.

Abstract: Base on the coupled three-dimensional model of flow temperature and apparent viscosity on semisolid materials, the mould filling processes of liquid and semisolid magnesium alloys have been analyzed. The simulation results showed that the semisolid mould filling with the characteristic of pseudo-plasticity and Bingham type is steady and the air entrapment is much smaller than that of liquid die casting. Therefore, the semisolid die casting can prevent from those defects produced by the traditional die casting, which offer a new technology for lower interior defects and better quality.

Abstract: In-situ neutron diffraction has been used to study the pseudoelastic-like behaviour of hydrostatically extruded AZ31 magnesium alloy during stress-strain cycles in compression and tension along the extrusion direction. It has been confirmed that the activation of reversal twinning processes during unloading is responsible for the macroscopically observed hysteresis effect. Moreover, neutron diffraction data reveals the existence of high tensile stresses in grains which have just experienced significant twinning activity prior to the start of the unload cycle. It is thus proposed that this tensile stresses provides the necessary driving force for the activation of untwinning in already twinned grains.

Abstract: The response of the relative resistivity changes to the isochronal annealing was measured in MgSc, MgScMn and MgYNdScMn alloys. The derivatives of the annealing curves were fitted by Gaussian functions to determine and separate the temperature ranges of the phase transformations taking place. The Austin-Rickett kinetics is argued to justify this procedure for diffusion driven transformations. TEM observation verified the conclusions drawn from the procedure.

Abstract: The cast magnesium alloys as AM50 offer a good strength, ductility and surface finish for automotive industry. But the poor creep resistance limited its application to power components such as engine and transmission cases at temperatures in excess of 100°C. In order to investigate the cyclic creep behavior of Magnesium Alloy at high temperature, creep tests of plate specimens AM50 were conducted in this work. Based on the analysis about the microstructure and defects of AM50 under the condition of cyclic creep, a cyclic creep constitutive model with isotropic and scalar damage parameter was developed. Furthermore, the proposed model was experimentally verified by analyzing the cyclic creep and recovery response of Cast Magnesium alloy under cyclic loading with dwell time. Comparisons between calculated results and experimental data showed good agreement.

Abstract: The dynamic fracture experiments were conducted on the heat treated magnesium alloys; AZ31B-O, AZ31B-200 °C, and AZ31B-430 °C. Cross shaped specimens with the crack on their center were used for the experiments. Dynamic fracture behavior near a crack tip under equal and unequal biaxial stress was observed by the caustics method. From the observation, the stress intensity factor and the fracture toughness value were calculated. As a result, the effect of heat treatment was found. However, no clear relation such as correlation between dynamic stress intensity factor and heat treatment temperature was deduced.