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
In this study the partially divorced eutectic microstructure ofα-Mg andβ-Mg17Al12was investigated by electron backscatter diffraction,transmission electron microscopy,and phase-field modeling in hypoeutectic Mg-Al a...In this study the partially divorced eutectic microstructure ofα-Mg andβ-Mg17Al12was investigated by electron backscatter diffraction,transmission electron microscopy,and phase-field modeling in hypoeutectic Mg-Al alloys.The orientation relationships between the individual eutecticαgrains,eutecticβphase,and primaryαgrains were investigated.While the amount of eutectic morphology is primarily determined by the Al content,the in-depth microstructure analyses and the phase-field simulation suggest non-interactive nucleation and growth of eutecticαphase in theβphase grown on the interdendritic primaryαdendrites.Also,phase-field simulations showed a preferred nucleation sequence where theβphase nucleates first and subsequently triggers the nucleation of eutecticαphase at the movingβphase solidification front,which supports the microstructural analysis results.展开更多
The effects of different amounts of added Al, ranging from 1 % to 9 %, on the microstructure and properties of Mg-Al binary alloys were investigated. The results showed that when the amount of added Al is less than 5%...The effects of different amounts of added Al, ranging from 1 % to 9 %, on the microstructure and properties of Mg-Al binary alloys were investigated. The results showed that when the amount of added Al is less than 5%, the grain size of the Mg-Al binary alloys decreases dramatically from 3 097 μm to 151 μm with increasing addition of Al. Further addition of Al up to 9% makes the grain size decrease slowly to 111 μm. The α-Mg dendrite arms are also refined. Increasing the amount of added Al decreases the hot cracking susceptibility of the Mg-Al binary alloys remarkably, and enhances the micro-hardness of the α-Mg matrix.展开更多
The microstructure and tensile properties were investigated in a thick-walled section （approximately 45 mm×43 mm） of a rheocast component produced by the RheoMetalTM process. Due to the long solidification peri...The microstructure and tensile properties were investigated in a thick-walled section （approximately 45 mm×43 mm） of a rheocast component produced by the RheoMetalTM process. Due to the long solidification period of such components, it is expected that the A1-Si eutectic formed will be coarse. Therefore, sodium （Na） was used as a modifying agent to reduce the coarseness of the eutectic. Tensile test bars were machined from three different sets of materials： 1） non-modified melt, 2） modified melt cast directly after Na addition, and 3） modified melt cast 30 min after Na addition. The alloy used was a secondary AlSi6Cu2.5 alloy （STENAL Rheol）, specially developed for rheocasting. The material was studied in the as-cast condition as well as after a T6 heat treatment. The results show that the Al-Si eutectic is significantly refined by the Na addition, even after a fading time of 30 min. However, it is observed that the Na modification generally has a detrimental effect on the mechanical properties, despite the structure refinement. This is especially true in the T6 heat treated condition, where the yield strength is reduced by more than 30%. Some possible mechanisms for the degradation of mechanical performance are discussed.展开更多
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.
基金supported by the Fundamental Research Program of Korea Institute of Materials Science(PNK7760 and PNK7770)the National Research Foundation of Korea(2020R1A2C2008416 and 2021M3H4A6A01049712)。
文摘In this study the partially divorced eutectic microstructure ofα-Mg andβ-Mg17Al12was investigated by electron backscatter diffraction,transmission electron microscopy,and phase-field modeling in hypoeutectic Mg-Al alloys.The orientation relationships between the individual eutecticαgrains,eutecticβphase,and primaryαgrains were investigated.While the amount of eutectic morphology is primarily determined by the Al content,the in-depth microstructure analyses and the phase-field simulation suggest non-interactive nucleation and growth of eutecticαphase in theβphase grown on the interdendritic primaryαdendrites.Also,phase-field simulations showed a preferred nucleation sequence where theβphase nucleates first and subsequently triggers the nucleation of eutecticαphase at the movingβphase solidification front,which supports the microstructural analysis results.
文摘The effects of different amounts of added Al, ranging from 1 % to 9 %, on the microstructure and properties of Mg-Al binary alloys were investigated. The results showed that when the amount of added Al is less than 5%, the grain size of the Mg-Al binary alloys decreases dramatically from 3 097 μm to 151 μm with increasing addition of Al. Further addition of Al up to 9% makes the grain size decrease slowly to 111 μm. The α-Mg dendrite arms are also refined. Increasing the amount of added Al decreases the hot cracking susceptibility of the Mg-Al binary alloys remarkably, and enhances the micro-hardness of the α-Mg matrix.
文摘The microstructure and tensile properties were investigated in a thick-walled section （approximately 45 mm×43 mm） of a rheocast component produced by the RheoMetalTM process. Due to the long solidification period of such components, it is expected that the A1-Si eutectic formed will be coarse. Therefore, sodium （Na） was used as a modifying agent to reduce the coarseness of the eutectic. Tensile test bars were machined from three different sets of materials： 1） non-modified melt, 2） modified melt cast directly after Na addition, and 3） modified melt cast 30 min after Na addition. The alloy used was a secondary AlSi6Cu2.5 alloy （STENAL Rheol）, specially developed for rheocasting. The material was studied in the as-cast condition as well as after a T6 heat treatment. The results show that the Al-Si eutectic is significantly refined by the Na addition, even after a fading time of 30 min. However, it is observed that the Na modification generally has a detrimental effect on the mechanical properties, despite the structure refinement. This is especially true in the T6 heat treated condition, where the yield strength is reduced by more than 30%. Some possible mechanisms for the degradation of mechanical performance are discussed.
