Zhe Leng

Influence of biocorrosion on microstructure and mechanical properties of deformed Mg-Y-Er-Zn biomaterial containing 18R-LPSO phase.

The microstructure and mechanical properties of as-extruded Mg-8Y-1Er-2Zn (wt%) alloy containing long period stacking ordered (LPSO) phase are comparatively investigated before and after corrosion in a simulated body fluid (SBF) at 37°C. The as-extruded alloy consists of a long strip-like 18R-LPSO phase and some fine lamellae grains formed by primary recrystallization during the extrusion process. The hydrogen evolution volume per day fluctuates between 0.21 and 0.32ml/cm(2) in the immersion test for 240h, and the corresponding corrosion rate is calculated as 0.568mm/y. The corrosion product is determined as Mg(OH)2, whilst a Ca(H2PO4)2 compound is also observed on the surface of the samples. The corrosion site preferentially occurs at the interface between LPSO phase and Mg matrix. Before immersing, the tensile yield strength (TYS), ultimate tensile strength (UTS) and elongation of the alloy are 275MPa, 359MPa, and 19%, respectively. More attractively, these mechanical properties can be maintained even after immersing in SBF for 240h (TYS, UTS and elongation are 216MPa, 286MPa and 6.8%, respectively) because of the existence of high anti-corrosion LPSO phase.

Structure stability and mechanical properties of high-pressure die-cast Mg-Al-Ce-Y-based alloy

With the aim to further improve the mechanical properties of Mg-Al-RE-based alloy, Mg-3.0Al-1.8Ce-0.3Y-0.2Mn alloy was prepared by high-pressure die-casting technique. The microstructure, thermal stability of intermetallic phases and mechanical properties were investigated. The results show that the alloy is composed of fine primary alpha-Mg dendrites and eutectic in the interdendritic regions. The intermetallic phases in eutectic are Al-11(Ce,Y)(3) and Al-2(Ce,Y) with the former being the dominant one. The thermal stability of Al-11(Ce,Y)(3) is conditioned. It is basically stable at temperature up to 200 degrees C within 800 h, while most of the Al-11(Ce,Y)(3) intermetallics transform to Al-2(Ce,Y) at higher temperature of 450 degrees C for 800 h. The alloy exhibits remarkably improved strength both at room temperature and 200 degrees C, which is mainly attributed to the reinforcement of dendrite boundaries with Al-11(Ce,Y)(3) intermetallics, small dendritic arm spacing effect as well as the solid solution strengthening with Y element.

Microstructures and Mechanical Properties of Mg-6Li-6.5Gd-1Dy-2Zn Alloys

Extrusion Mg-6Li-6.5Gd-1Dy-2Zn alloy was prepared successfully by vacuum melting. The microstructures and mechanical properties of as-cast and as-extruded Mg-6Li-6.5Gd-1Dy-2Zn alloys were investigated. Extruding process refines the α (Mg) phase and β (Li) phase, and makes the Mg3X phase crushed and dispersed well. After heat treatment, Mg3X phase particles became finer and much more RE enriched phase particles formed in the matrix. These effects result in the improvement of mechanical properties of the alloys. In this study, after solution treated at 510°C for 3h and aged at 215°C for 99h, the as-extruded alloy exhibits the best mechanical properties, and the microhardness, ultimate tensile and elongation reach 103.0, 249 MPa and 34.8%, respectively.