Ruizhi Wu

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.

New horizon for high performance Mg-based biomaterial with uniform degradation behavior: Formation of stacking faults.

Designing the new microstructure is an effective way to accelerate the biomedical application of magnesium (Mg) alloys. In this study, a novel Mg–8Er–1Zn alloy with profuse nano-spaced basal plane stacking faults (SFs) was prepared by combined processes of direct-chill semi-continuous casting, heat-treatment and hot-extrusion. The formation of SFs made the alloy possess outstanding comprehensive performance as the biodegradable implant material. The ultimate tensile strength (UTS: 318 MPa), tensile yield strength (TYS: 207 MPa) and elongation (21%) of the alloy with SFs were superior to those of most reported degradable Mg-based alloys. This new alloy showed acceptable biotoxicity and degradation rate (0.34 mm/year), and the latter could be further slowed down through optimizing the microstructure. Most amazing of all, the uniquely uniform in vitro/vivo corrosion behavior was obtained due to the formation of SFs. Accordingly we proposed an original corrosion mechanism for the novel Mg alloy with SFs. The present study opens a new horizon for developing new Mg-based biomaterials with highly desirable performances.

Microstructure and mechanical properties of Mg–8Li–(1, 3)Al–(0, 1)Y alloys

Abstract The microstructure and mechanical properties of Mg–8Li–(1, 3)Al–(0, 1)Y alloys were studied. Y refines and spheroidises the microstructures of alloys, and it causes the decrease in α phase percentage. Blocky AlY exists in α and β phases. When Al content is 3 wt-%, AlLi and MgLi2Al form in β phase. The Al content solid soluted in the α phase appears larger than that in the β phase, while the Y content solid soluted in the α phase is less than that in the β phase. The addition of Al and Y brings about a combination of good strength and elongation for the Mg–8Li alloy.

Enhancing the performance of Mg-based implant materials by introducing basal plane stacking faults

One of the keys to allowing Mg alloys to serve as biodegradable materials is how to balance their degradation behaviours and mechanical properties in physiological environment. In this study, a novel Mg-6Ho-0.5Zn alloy (wt%) containing profuse basal plane stacking faults (SFs) is prepared. This newly-developed alloy with SFs exhibiting uniform corrosion behaviour, low corrosion rate and high mechanical properties, as compared to the classic Mg-Ho based alloys (Mg-6Ho and Mg-6Ho-1.5Zn). Furthermore, the Mg-6Ho-0.5Zn alloy shows no significant toxicity to Saos-2 cells. An original uniform corrosion mechanism is proposed by combining the special defect structure, orientation of SFs and promptly effective corrosion film. The development of the new microstructure for Mg-Ho based alloys with desirable corrosion performance has important implications in developing novel degradable Mg-based implant materials.

Effect of alloying elements on the texture and the anisotropy of the mechanical properties of magnesium alloys with REM, lithium, and aluminum

The formation of the texture and the anisotropy of the mechanical properties in extruded rods of commercial alloys MA5, MA18, MA21 and also experimental Mg-Y-based and Mg-Y-Ce-based alloys are studied by X-ray diffraction and the measurement of the hardness and the tensile and compressive properties. It is shown that the magnesium alloys can be separated into three groups according to the anisotropy of the mechanical properties. The first group consists of the alloys not containing rare-earth metals and lithium, and the second group is the alloys with yttrium for which the yield strength in the axial direction of the rods are significantly higher than those in the transverse direction. The alloys of the first group demonstrate a substantial excess of the yield strength in the axial direction in the tension tests as compared to those in compression tests, and the second group alloys do not demonstrate such a difference. The ceriumand lithium-containing alloys (the third group) exhibit a weak anisotropy of the strength properties. A method for estimating the anisotropy of the strength properties is developed on the basis of calculation of the Taylor factors for basal slip averaged over all orientations of crystallites, and a quantitative method is developed for determining the phase composition by measuring the solid solution lattice parameter.

Microstructure and texture evolution of Mg–Li alloy during rolling

Abstract This paper investigates the microstructure and texture evolution of as-rolled Mg-5Li-3Al-2Zn-1.2Y-0.8Nd. During rolling (both warm rolling and hot rolling), many twins appear in the alloy, some of which are cross-twins. Dynamic recrystallization occurs, resulting in grain refinement. With the increase of rolling reduction percentage, basal texture appears, and then finally non-basal texture appears. The non-basal texture during warm rolling begins to appear under a smaller rolling reduction percentage than that during hot rolling. When the rolling reduction is 28 %, the angles between the majority of c-axes and rolling direction are mainly about 25°. When the rolling reduction percentage is 52 %, the textures are strengthened.

EFFECTS EVALUATION FOR DIFFERENT RARE EARTH ELEMENTS IN MAGNESIUM-LITHIUM ALLOY

1 wt.% different rare earth elements (Ce, Y, Gd, misch metal, Nd) are added into the alloy of Mg6Li-1.5Al, respectively. The different effects on the microstructure and mechanical properties are evaluated. The additions of these elements produce granular and rod-like precipitated phases, which are Al2Ce, Al2Y, AlGd, Al3La, Al2Nd, respecitvely. All the rare elements have refining effects in the alloys. Misch metal and Nd have the best refining effects, while Y and Ce have the least obvious refining effects. All the elements are favorable for the improvement of strength and elongation. Mg6Li-1.5Al-1Ce possesses the highest strength, and Mg-6Li-1.5Al-1Y possesses the highest elongation. If considering the different yield of elements, Mg-6Li-1.5Al-1Y possesses both the highest strength increase per rare earth yield and elongation increase per rare earth yield.

Microstructure and Hardness of Mg – 9Li – 6Al Alloy After Different Variants of Solid Solution Treatment

The microstructure and the hardness of cast magnesium alloy Mg – 9% Li – 6% Al are studied after a treatment for solid solution at 300, 350, and 450°C for 0.5 – 5 h. The phase composition of the alloy is represented by α-Mg, β-Li, thin-plate and faceted particles of an AlLi phase, and particles of a MgLi2Al θ-phase. The θ-phase dissolves in the matrix in the initial stage of the solution treatment, which causes growth in the hardness of the alloy. At a temperature above 350°C the AlLi phase dissolves giving way to short rod-like precipitates of a θ-phase, which remain steady in the process of solution treatment. The hardness of the alloy deceases in this stage for this reason.

Microstructural stability of heat-resistant high-pressure die-cast Mg-4Al-4Ce alloy

Abstract The thermal stability of Al-RE (rare earth) intermetallic phases with individual RE for heat-resistant high-pressure die-casting Mg–Al–RE alloys is investigated. The results of this study show that the main strengthening phase of Mg-4Al-4Ce alloy is Al11Ce3, whose content is about 5 wt.% according to quantitative X-ray diffraction phase analysis. The Al11Ce3 phase appears to have high thermal stability at 200 °C and 300 °C, while phase morphology change with no phase structure transition could occur for Al11Ce3 when the temperature reaches 400 °C. Furthermore, besides the kinds of rare earths and temperature, stress is also an influencing factor in the microstructural stability of Mg-4Al-4Ce alloy.

The deformation behavior and microstructure evolution of duplex Mg-9Li-1Al alloy during superplasticity tensile testing

The superplastic mechanical properties and microstructure evolution of the duplex Mg-9Li-1Al alloy were investigated. The tensile testing results show that, the elongation of the as-extruded Mg-9Li-1Al alloy reaches 510% at 573 K with a strain rate of 2×10-4 s-1. During the deformation process, the strips of α phase break into equiaxed structure. This phenomenon can be attributed to a particular dynamic recrystallization, which suggests that the β phase can recrystallize in the α phase due to the small misfit degree between α phase and β phase.