Papers by Author: Qun Yi Wei

Abstract: Mg-9Li-3Al-xSr (x=0wt%, 1.0wt%, 2.0wt%, 2.5wt%) magnesium alloys with different ingot sizees were prepared in furnace under the protection of argon atmosphere. The as-cast microstructure and solidification characteristics of Mg-9Li-3Al-xSr alloys were experimentally examined using optical microscopy, scanning electron microscopy and X-ray diffraction. The results indicate that Mg-9Li-3Al-xSr alloys are composed of α-Mg, β-Li, Mg₁₇Al₁₂, AlLi and Al₄Sr phase. The grains of Φ10mm ingots are much smaller and the compound phase distributes much more uniformly than Φ90mm ingots. Solidification process of Mg-9Li-3Al-xSr alloys follows the principle of eutectic solidification. The microstructure of the series as-cast alloys is typical rodlike eutectic microstructure.

Abstract: Mg-9Li-3Al-xSr alloys were prepared in vacuum furnace under the protection of argon atmosphere. Effects of Sr content on microstructure and mechanical properties of as-cast Mg-9Li-3Al alloys were investigated. The results indicate that α-Mg and β-Li phases exist in all alloys. The addition of Sr causes grain refinement of the test alloys and new Al₄Sr phase is formed in the alloys. The mechanical properties of alloys initially increase and then decrease with the increase of Sr content. Sr has obvious refining effect on the alloys and the distribution of Al₄Sr phase is much more uniformly when Sr content is 2.5wt%,. The as-cast Mg-9Li-3Al-2.5Sr alloy exhibits an optimum combination of mechanical properties with the ultimate strength, yield strength and elongation of 186MPa, 149MPa and 11% respectively, improving obviously compared with Mg-9Li-3Al alloy. With the continuing increase of Sr content, the mechanical properties of the test alloys decrease.

Abstract: Mg-Sr alloy was prepared by the vacuum synchronous reduction method at a temperature of 1100°C. The phase composition of the reaction product and slag was analyzed by XRD. Results showed that Mg17Sr2 and α-Mg were formed in the product while Ca2SiO4 and Sr2SiO4 existed in the slag. DSC-TG curves obtained from thermal analysis of the reduction process indicated that vacuum was an essential condition in the preparation of Mg-Sr alloy by synchronous thermal reduction method when temperature was below 1200°C.

Abstract: The species and shapes of impurities in magnesium alloy melt were studied. Floatation Refining method of Magnesium Alloys melt and eduction dynamics analysis were used to judge the floatation condition of gas bubble with MgO impurity. Models of floatation eduction were established to study the dynamics relationship of weight, drag and buoyancy. The relation curve between refining gas bubble radius and floating up rate was established. The choice method of gas bubble radius was provided and a practical process scheme proposed for floatation refining of magnesium alloys melt.

Abstract: The samples with different strontium contents of AE42 magnesium alloy were prepared. The metalloscope and electronic microscope and XRD were used to characterize the microstructure and composition of the samples. The elevated temperature mechanical properties of the samples were tested and the strontium phases in the AE42 and their influence to the mechanical properties analyzed. The results showed that the main strontium phase in the AE42 was Al4Sr. Al4Sr pinned the crystal boundary of magnesium matrix and hindered dislocation climbing and sliding through the crystal boundary effectively. As a result, the crystal axial range was reduced and the crystal grain refined, and hence the creep resistance increased.

Abstract: Suspended on Mg-base melt, SrCl2 was electrochemical reduced to prepare Mg-Sr alloy. The kinds of Sr-compounds, composition ratio of flux, temperature of molten salt and Mg-base molten bath and recovery of Sr were discussed. According to theories and experiments, this paper presents the relations between the adding flux and reduction of Sr-compounds with the technical parameters. The electrode reactions and the Gibbs Free Energies were evaluated based on thermodynamics analysis. The results show that composition of flux played important roles in the reduction process. The optimized technical flow and parameters for the application of the new method were advised.

Abstract: The Air-acetylene Flame Atomic Absorption Spectrometry (FAAS) was used to measure Sr content in Mg-Sr Alloys. The experiment conditions including acetylene flow rate, measurement height, flame wavelength were studied and the disturbing factors were discussed. It was found that, as dissolution agent of alloys and LaCl3 as the deionization agent and flame wavelength being 460.7nm, the detection limits is 1.16mg/L and the relative standard deviations is less than 0.3% and the recovery rates of Sr is more than 95%. The advantages of this method were summarized as: high sensitivity and precision, low chemistry disruption, good selectivity, good recurrence characteristics of the measuring conditions. The method is suitable for the control analysis and sample-system analysis of determination Sr content in the Mg-Sr Master Alloys.

Abstract: At the present Mg-Sr alloy is usually produced by alloy mixing process or melt-leaching-reduction process which has low productivity. A new process has been developed termed “Preparation Mg-Sr alloys using vacuum thermal reduction”. The principle and procedure of the new process were discussed in this paper. The reduction thermodynamics was analyzed, including establishing the oxygen potential diagram of Sr, Mg, Si and Al, determination of main reactions, and evaluation of Gibbs free energy in vacuum. The results showed that Mg-Sr alloys can be obtained by synchronous reduction of SrO and MgO from a mixture of MgO, SrO, Si, CaO. The equipment, reduction temperature and vacuum for the new process have been also discussed.

Abstract: In this paper, effects of strontium on Mg alloys and preparation technology of Mg-Sr and Mg-Sr-Al master alloys were summarized respectively. Prospects and applications of Sr-Mg master alloys were analyzed too. The results showed that thermodynamics calculation of reaction between SrO and Mg(l) showed that molten Mg can reduce SrO, in which excess of molten. The microstructure of hypoeutectic Mg-Sr binary alloys is composed of primary Mg matrix, and laminary eutectic phase(Mg-Mg17Sr2),but the microstructure of Mg-Sr-Al alloy consists of plate-like primary Al4Sr, laminary eutectic phase (Mg-Mg17Sr2 or Mg-Mg17Al12 or Mg-Mg17Sr2-Mg17Al12) embedded in primary dendrites of magnesium matrix. Additive strontium in Mg alloys can refine it grains, reduce degree of porosity, improve mechanical and thermal properties, therefore, Mg-Sr master alloys can be served widely as an additive for modification or as a constituent of Mg alloys, Al alloys, Zn alloys, etc.