Papers by Author: Jia Cheng Gao

Abstract: The yields and uniformities of Mn in high Mn-content (Mn≥10wt%) Mg-Mn master alloys have been studied in this paper. Pure Mn powder and Mg ingot were used to be raw materials and put into graphite pot. The master alloys were prepared by stirring cast in an induction furnace with Ar protection atmosphere at the operating power of 10KW. Master alloy melts were cooled in three different conditions, which were cooling in air with graphite pot, cooling in water with graphite pot and cooling in copper mould. The contents and distribution of Mn in master alloys were tested by GB\T 1506-2002. The results shown that the yields of Mn were improved with the increase of Mn particle size and the better uniformity was obtained by faster cooling speed of master alloy melt and smaller particle size of Mn powder, which were agree with the calculated results.

Abstract: In this paper, alloy with composition of MgMnAlZnCu was designed by using the strategy of equiatomic ratio and high entropy of mixing. The microstructure and mechanical parameters of the new high entropy alloy cooling in three conditions were studied. The alloy was prepared by induction melting and then it was cast in copper molds in air, water and salt water respectively. The microstructure and properties of alloy samples were examined by microhardness tester, XRD, TEM, SEM and testing machine for material strength. The results showed that the alloy was composed mainly of h.c.p and Al-Mn quasicrystal phases. The alloy exhibit high hardness (431HV-467HV) and high compression strength (428MPa-450MPa) at room temperature. The alloy was fragile and the strains were from 3.29% to 5.53%.

Abstract: In this paper, alloys with compositions of Mgx(MnAlZnCu)100-x (x: atomic percentage; x=20, 33, 43, 45.6 and 50 respectively) were designed by using the strategy of equiatomic ratio and high entropy of mixing. Microstructure and mechanical properties of the new high entropy alloy were studied. The alloys were prepared by induction melting and then were cast in a copper mold in air. The alloy samples were examined by microhardness tester, XRD, SEM, thermal analyzer and testing machine for material strength. Alloys were composed mainly of h.c.p phase and Al-Mn icosahedral quasicrystal phases. The alloys exhibited moderate densities which were from 4.29g•cm-3 to 2.20g•cm-3, high hardness (429HV-178HV) and high compression strength (500MPa-400MPa) at room temperature. The extensibility was increased with Mg from 20at% (atomic percentage) to 50at%.

Abstract: Compared with the actual operation, computational simulation will save the cost and provide more valuable references or guiding significance for the real production. Using professional forming software DEFORM-3D, the upsetting process of WE43 magnesium alloy was simulated. Based on the actual flow stress data, the simulation model of WE43 magnesium alloy was created in DEFORM-3D. Results show that the uniform distribution of the temperature of WE43 magnesium alloy during the forming process is beneficial to the structural homogeneity and contributes to excellent flowing property. There is the stress concentration in the edge and slide face of the billet. So during the process of compression, the fracture will appear earlier in the edge and slide face of the sample.

Abstract: Magnesium alloys are considered as candidate materials for biodegradable implants. However, the key issue is that they corrode too fast in physiological environment. The aim of this study is to investigate the effect of microstructure and texture of magnesium alloys on their corrosion resistance. Magnesium alloy AZ31 extruded rod, hot rolled sheet and extruded sheet with different initial microstructure and texture were prepared. Then they were immersed in conventional simulated body fluid (SBF) for several days for corrosion evaluation. The corrosion products and precipitates on their surfaces were examined by scanning electron microscopy (SEM). The preliminary results showed that the initial microstructure and texture of AZ31 alloys has considerable effect on the weight loss rate of the alloys, suggesting that it is possible to enhance the corrosion resistance of AZ31 alloys through tailoring the microstructure and texture of the alloys.

Abstract: The corrosion and degradation behavior of Mg-Ca binary alloy in simulated body fluid (SBF) were studied by immersion of pure Mg and Mg-Ca alloys with different Ca contents in SBF. The corrosion process was carried out by real-time measurement of sample weight, pH value of SBF and the microstructures of the immersed samples at different immersion time observed by electron microscopy. The result shows that Mg-Ca alloy with 0.7% Ca has better corrosion resistance than the one with 2.0% Ca. The product generated on the surface of Mg-0.7Ca during the immersion was identified by X-ray diffraction and energy spectrum analysis.

Abstract: The nano-particle pyrite in nano-particle form was synthesized by the deposition hydrothermal reaction using FeCl3•6H2O, Na2S•9H2O and S as the starting materials. The property of particles was investigated by X-ray diffraction, transmission electron microscope, UV-Vis spectrophotometer. The results indicated that the pure iron pyrite could be achieved in the alkaline condition. Increasing the proportion of S avails to removing marcasite and ferric oxide . Wwhen the amount of FeCl3, Na2S and S is in the ratio of 1:3:1.5, the product is pure pyrite FeS2 powder with a polyhedron shape is obtained and the average particle size isof about 20~40nm, and this result can be easily repeated. Optical analysis indicates that the optic energy band gap is about 1.62 eV. Its open circuit voltage is 456mV, and the corresponding short circuit current is 19 μA.

Abstract: Nano-TiO2 synthesized by hydrolysis of TiCl4 demonstrated high reactivity in presence of peroxide hydrogen under visible light (λ>420nm).The nano-TiO2 powders were characterized by XRD, Uv-Vis, FT-IR. The results showed that the TiO2 nanocatalyst sensitized with peroxide hydrogen could absorb visible light up to 550nm, and Vis absorption could be extended to 600 nm for the sulfated TiO2 .Photocatylytic degradations of methyl orange and methylene blue were above 90% for sulfated TiO2 in 180min. The inorganic sulfate species absorbing on the surface of titania were mainly responsible for the high activity of the TiO2 under visible light regions．

Abstract: The specific gravity and elastic modulus of magnesium alloys are similar to that of human bone. Magnesium is one of the most important elements in the human body and plays a key role in the metabolic process. But the application of magnesium is seriously limited as a biomaterial since it corrodes easily in the physiological environment of the body. In order to reduce the corrosion, we developed protective films using rare earth (RE) conversion processing. The surface of magnesium samples was modified by contact with different rare-earth salt solutions; then the samples were dipped in SBF to test their corrosion resistance. The change of mass and the pH of the solutions were measured continuously using an electronic scale and a pH micrometer. The surface microstructure of the samples was observed by XRD and metallomicroscope. Corrosion rates of the samples in SBF were determined using Taffier curve. The preliminary results show that the conversion treatment with CeCl3 or Y(NO3)3 can improve the corrosion resistance of magnesium in SBF. The relationship of the RE salts concentration and the corrosion properties were studied,the best combination of parameters was determined, and the formation mechanism of rare-earth conversion film has been also elaborated.

Abstract: Recently, there has been an increasing interest in magnesium as biomaterials due to its similar elastic modulus, density and strength to that of human bone than other currently popularly used metallic biomaterials. However, the knowledge of its biocompatibility is lacking. This paper reports the results of testing the cytotoxicity, haemolysis and acute toxicity on untreated and treated magnesium samples. The results showed that no cytotoxicity was detected on untreated magnesium samples. However, samples of alkali-treated magnesium caused distinct morphological changes on cells with a reduction in cell number vs the control group. In haemolysis tests, untreated magnesium showed a haemolytic effect, whereas there was a small haemolytic effect (2.2%) on alkali heat-treated metal; this is less than the allowable 5%. Magnesium samples coated with an organic film show the lowest haemolytic effect. No acute toxicity was observed; no animal deaths occurred and we observed no obvious weight differences in untreated magnesium vs organic coated samples compared to the control group.