The effect of yttrium and mischmetal(MMs) on the as-cast and solid solution treated structures of Mg-Al alloys with different Al-contents was investigated. The results show that the MMs in Mg-Al alloy existed in rod A...The effect of yttrium and mischmetal(MMs) on the as-cast and solid solution treated structures of Mg-Al alloys with different Al-contents was investigated. The results show that the MMs in Mg-Al alloy existed in rod Al 4(Ce, La)compound while Y in Mg-Al alloy in polygonal Al 2Y compound. The amount of Mg 17Al 12 in Mg-Al alloy is decreased with increasing Y or MMs addition, and Mg 17Al 12 intermetallic compound is changed from continuous network to discontinuous one. The Al 4(Ce, La) and Al 2Y compounds are not dissolved into Mg-Al alloy matrix during solid solution treatment so that their high heat stability can be exhibited. The experiment of mechanical properties indicate that elongation and impact toughness of the Mg-Al-Y alloy with polygonal Al 2Y compound are higher than those of Mg-Al-MMs alloy with rod Al 4(Ce, La) compound.展开更多
A multi-grain phase field model coupled with thermodynamic calculation was adopted to describe the dendritic growth in pressurized solidification of Mg-A1 alloy during squeeze casting, in which the effects of the pres...A multi-grain phase field model coupled with thermodynamic calculation was adopted to describe the dendritic growth in pressurized solidification of Mg-A1 alloy during squeeze casting, in which the effects of the pressure on the Gibbs free energy and chemical potential of solid and liquid phases, the solute diffusion coefficient, and the solute partition coefficient were considered. The individual effect of solute diffusion coefficient, and the Gibbs free energy on the dendritic growth was studied. With the compar- ison of the dendritic growth under atmospheric and elevated pressures, the effect of pressure on the microstructure evolution was discussed. The results showed that the grains are refined, the dendritic growth rate tends to increase and the secondary dendrite arms are more developed as the pressure is increased from 0.1 to 100 MPa, which showed a good agreement with the experimental results of direct squeeze casting of Mg-AI alloy. As the pressure increases, the largest dendritic growth rate can be obtained under the pressure between 200 and 250 MPa, while the growth rate decreases with a further increase of pressure.展开更多
Directionally solidified binary Mg-Al eutectic alloy wires of approximately 5 mm in diameter were produced by the Ohno continuous casting （OCC） process and the microstructure was examined. It was found that the wire...Directionally solidified binary Mg-Al eutectic alloy wires of approximately 5 mm in diameter were produced by the Ohno continuous casting （OCC） process and the microstructure was examined. It was found that the wires possess obvious unidirectional growth characteristic along its axial direction. The microstructure consists of parallel columnar grains that resulted from the competitive growth of equiaxed grains solidified on the head of dummy bar. Each columnar grain comprises regular eutectic a-Mg and β-Mg17 Al12 phases, which grew along the axial direction of the wires. The morphology of the eutectic is mainly lamellar, meanwhile rod eutectic exists. The formation of rod eutectic was attributed to the ＂bridging effect＂ caused by incidental elements in the alloy.展开更多
文摘The effect of yttrium and mischmetal(MMs) on the as-cast and solid solution treated structures of Mg-Al alloys with different Al-contents was investigated. The results show that the MMs in Mg-Al alloy existed in rod Al 4(Ce, La)compound while Y in Mg-Al alloy in polygonal Al 2Y compound. The amount of Mg 17Al 12 in Mg-Al alloy is decreased with increasing Y or MMs addition, and Mg 17Al 12 intermetallic compound is changed from continuous network to discontinuous one. The Al 4(Ce, La) and Al 2Y compounds are not dissolved into Mg-Al alloy matrix during solid solution treatment so that their high heat stability can be exhibited. The experiment of mechanical properties indicate that elongation and impact toughness of the Mg-Al-Y alloy with polygonal Al 2Y compound are higher than those of Mg-Al-MMs alloy with rod Al 4(Ce, La) compound.
基金funded by the National Natural Science Foundation of China (Grant No.51175291)Tsinghua University Initiative Scientific Research Program(Grant No.2011Z02160)the State Key Laboratory of Automotive Safety and Energy,Tsinghua University under the contract 2013XC-A-01
文摘A multi-grain phase field model coupled with thermodynamic calculation was adopted to describe the dendritic growth in pressurized solidification of Mg-A1 alloy during squeeze casting, in which the effects of the pressure on the Gibbs free energy and chemical potential of solid and liquid phases, the solute diffusion coefficient, and the solute partition coefficient were considered. The individual effect of solute diffusion coefficient, and the Gibbs free energy on the dendritic growth was studied. With the compar- ison of the dendritic growth under atmospheric and elevated pressures, the effect of pressure on the microstructure evolution was discussed. The results showed that the grains are refined, the dendritic growth rate tends to increase and the secondary dendrite arms are more developed as the pressure is increased from 0.1 to 100 MPa, which showed a good agreement with the experimental results of direct squeeze casting of Mg-AI alloy. As the pressure increases, the largest dendritic growth rate can be obtained under the pressure between 200 and 250 MPa, while the growth rate decreases with a further increase of pressure.
基金the Shaanxi Provincial Natural Science Research Project(No.2003E111)Scientific research project of Education Department of Shaanxi Province(No.07JK358)the Industrialization Cultivation Project of Education Department of Shaanxi Province(No.04JC24).
文摘Directionally solidified binary Mg-Al eutectic alloy wires of approximately 5 mm in diameter were produced by the Ohno continuous casting （OCC） process and the microstructure was examined. It was found that the wires possess obvious unidirectional growth characteristic along its axial direction. The microstructure consists of parallel columnar grains that resulted from the competitive growth of equiaxed grains solidified on the head of dummy bar. Each columnar grain comprises regular eutectic a-Mg and β-Mg17 Al12 phases, which grew along the axial direction of the wires. The morphology of the eutectic is mainly lamellar, meanwhile rod eutectic exists. The formation of rod eutectic was attributed to the ＂bridging effect＂ caused by incidental elements in the alloy.
