Papers by Author: Yao Ming Wu

Abstract: Mg-5Y-3Nd-Zr-xGd (x=0 and 4 wt.%) alloys were prepared by metal mould casting, and aging behavior, mechanical properties and fracture morphology were investigated. The result shows that after T6 treatment, the massive eutectic phase in as-cast alloys dissolved and finer Mg5RE phase precipitated dispersively in the matrix, and mechanical properties were improved simultaneously. Mg-5Y-3Nd-4Gd-Zr alloy exhibits good age hardening behavior and the peak hardness is about 20% higher than the Gd-free alloy. Gd addition can significantly improve mechanical properties of the alloy especially at the elevated temperature. The ultimate tensile strength and yield strength of Mg-5Y-3Nd-4Gd-Zr alloy at 250°C, with the value of 276 and 168 MPa, respectively, are over 20% higher than those of the Gd-free alloy. It is mainly attributed to the increase and homogeneous distribution of the fine heat-resistant Mg5RE precipitate in the matrix.

Abstract: The lightest density of Mg has stimulated renewed interest in Mg based alloys for applications in the automotive, aerospace and communications industries. However, Mg in the pure form has relatively low strength, limited ductility and is susceptible to corrosion. Great efforts have been made to improve the mechanical properties of Mg alloys. Alloying Mg with other elements is one of the most important methods. An important class of Mg alloys is the Mg-Zn-RE system (RE = rare earth elements). In recent few decades, a series of new Mg-Zn-RE system alloys have been obtained, and detailed the structure and mechanical properties of the alloys. In this paper, the structure and mechanical properties of the Mg-Zn-RE alloys have been summarized. It showed that these alloys have high strength and they are prospected to be widely used in the future.

Abstract: The Mg-8Zn-8Al-4RE (RE = mischmetal, mass%) magnesium alloy was prepared by using casting method. The microstructure and mechanical properties of as-cast alloy, solid solution alloy and aged alloy samples have been investigated. Optical microscopy, X-ray diffractometery and scanning electron microscope attached energy spectrometer were used to characterize the microstructure and phase composition for the alloy. Net shaped τ-Mg32(Al,Zn)49 phase was obtained at the grain boundary, and needle-like or blocky Al11RE3 phase disperses in grain boundary and α-Mg matrix. The τ-Mg32(Al,Zn)49 phase disappeared during solution treatment and a new phase of Al2CeZn2 formed during subsequent age treatment. The mechanical properties were performed by universal testing machine at room temperature, 150 °C and 200 °C, separately. The ultimate tensile strength of as-cast alloy is lower compared to an age treatment alloy at 200 °C for 12h. The strengths decreased with enhancing test temperature, but elongation has not been effect by age treatment.

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: A powder material of Mg-Ni-Cu-Y was synthesized by mechanical alloying method. Considerable amounts of amorphous and nanocrystalline phases formed after a mixture of elemental powder with the overall composition of Mg78Ni9Cu11Y2 was mechanical alloyed for 200 h. The phase formed in the synthesized powder materials was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The electrochemical properties were examined with a solution of 6M KOH.