In the present research, microstructure refinement of a high-Nb TiAl alloy(Ti-48Al-8Nb-0.15B) was realized by means of the electromagnetic continuous casting(EMCC) technique. The microstructure of an ingot obtained by...In the present research, microstructure refinement of a high-Nb TiAl alloy(Ti-48Al-8Nb-0.15B) was realized by means of the electromagnetic continuous casting(EMCC) technique. The microstructure of an ingot obtained by EMCC was analyzed using scanning electron microscopy(SEM). As compared with the raw as-cast al oy, the obtained EMCC alloy presented a much finer microstructure with lamellar colonies with a mean size of about 50-70 μm because the electromagnetic stirring broke initial dendrites and enhanced the heterogeneous nucleation. As the grains were refined, the properties of the TiAl alloy were improved significantly. This implies that the EMCC technique could offer the possibility of application for high-Nb TiAl alloys with a refined microstructure and excel ent properties to be used as a structural material.展开更多
For the large magnesium alloy ingot, there is a considerable difference in cooling rate of different parts in the ingot, which leads to non-uniform distribution of the secondary phases, solute segregation and tensile ...For the large magnesium alloy ingot, there is a considerable difference in cooling rate of different parts in the ingot, which leads to non-uniform distribution of the secondary phases, solute segregation and tensile properties. In the present research, an heavy AZ61 alloy ingot with a diameter of 500 mm was made by semi-continuous casting. The microstructure and mechanical properties at different positions along the radial direction of the large ingot were investigated by using an optical microscope(OM), a scanning electron microscope(SEM), an energy dispersive spectroscope(EDS), and a micro-hardness tester. The results indicate that the microstructure of the AZ61 ingot is non-uniform in different locations. It changes from equiaxed to columnar grains from the center to the edge; the average grain size gradually reduces from 1,005 μm to 763 μm, the secondary dendrite arm spacing reduces from 78 μm to 50 μm, and the Mg17(Al,Zn)12 phase is also refined. The micro-hardness value increases from 55.4 HV at the center to 72.5 HV at the edge of the ingot due to the microstructure differences, and the distribution of micro-hardness at the edge of the ingot is more uniform than that in the center. The tensile properties at room temperature show little difference from the center to the edge of the ingot except that the elongation at the edge is only 3.5%, much lower than that at other areas. The fracture mechanism is ductile fracture at the center and cleavage fracture at the edge of the ingot, and at the 1/2 radius of the ingot, a mixture of ductile and cleavage fracture is present.展开更多
The relationship between electromagnetic frequency and microstructures of continuous casting aluminum alloys was studied. 7075 aluminum alloy ingot of 100 mm in diameter was produced by electromagnetic continuous cast...The relationship between electromagnetic frequency and microstructures of continuous casting aluminum alloys was studied. 7075 aluminum alloy ingot of 100 mm in diameter was produced by electromagnetic continuous casting process, the microstructures of as-cast ingot was examined by scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS). The results showed that electromagnetic frequency greatly influenced segregation and microstructures of as-cast ingot, and product quality can be guaranteed by the application of a proper frequency. Electromagnetic frequency plays a significant role in solute redistribution; low frequency is more efficient for promoting solution of alloying elements.展开更多
The super high strength aluminum alloy ingots with 100 mm in diameter were cast by the process of low-frequency electromagnetic horizontal continuous casting (LFEHC) and the effect of electromagnetic field on the as-c...The super high strength aluminum alloy ingots with 100 mm in diameter were cast by the process of low-frequency electromagnetic horizontal continuous casting (LFEHC) and the effect of electromagnetic field on the as-cast microstructure was studied. Results show that microstructure of the sample prepared by the LFEHC process was greatly refined. Microstructures at the border and the center of the ingots were fine, uniform and rosette-shaped. Electromagnetic frequency plays a key role in microstructure refining. Fine and uniform microstructures can be obtained with optimal electromagnetic frequency. In this experiment, under a frequency of 30 Hz the microstructure was the finest and the most uniform.展开更多
AZ31 alloy billets of 200 mm in diameter were produced by three different processes of conventional direct chill (DC) casting, low-frequency electromagnetic casting (LFEC) and low-frequency electromagnetic vibrati...AZ31 alloy billets of 200 mm in diameter were produced by three different processes of conventional direct chill (DC) casting, low-frequency electromagnetic casting (LFEC) and low-frequency electromagnetic vibration casting (LFEVC), respectively. The effect of LFEC and LFEVC on the microstructures, macmsegregation and mechanical properties of AZ31 alloy billets was investigated. In conventional DC casting, the AZ31 alloy billets exhibited coarse grains (about 370 μa) and severe segregation of A1 and Zn. In the presence of a solo low-frequency alternating magnetic field or a low-frequency electromagnetic vibration field applied during DC casting of Ф200 mm AZ31 billets, grains in the AZ31 alloy billets were effectively reffmed (about 210 μa) and the macrosegregation of A1 and Zn in the billets was greatly decreased. Furthermore, the tensile strength, fracture elongation and hardness of the as-cast AZ31 alloy billets were improved by the processes of LFEC and LFEVC relative to that cast by the process of conventional DC casting.展开更多
Under the high-intensity ultrasonic field,AZ80 magnesium alloy was semi-continuously cast.The effects of ultrasonic intensity on the as-cast microstructures and mechanical properties were investigated.The results show...Under the high-intensity ultrasonic field,AZ80 magnesium alloy was semi-continuously cast.The effects of ultrasonic intensity on the as-cast microstructures and mechanical properties were investigated.The results show that the microstructures of the alloy cast under high-intensity ultrasonic field are fine and uniform,and the grains are equiaxed,rose-shaped or globular with an average size of 257μm.High-intensity field significantly decreases the grain size,changes the morphologies of theβ-Mg17Al12 phases and reduces their area fraction.It is also shown that a proper increase in ultrasonic intensity is helpful to obtain fine,uniform and equiaxed as-cast microstructures.The optimum ultrasonic parameters are that frequency is 20 kHz and ultrasonic intensity is 1 368 W.The mechanical tests show that the mechanical properties of the as-cast AZ80 magnesium alloy billets cast under ultrasonic field are greatly improved,and with increasing the ultrasonic intensity,the mechanical properties of the entire alloy billets are much higher and more uniform than those of the alloy without ultrasonic field.展开更多
LY12 aluminum alloys made by electromagnetic casting (EMC) and direct chill casting (DCC), were analyzed by optical microscope, differential scanning calorimetry, transmission electron microscope and X ray diffraction...LY12 aluminum alloys made by electromagnetic casting (EMC) and direct chill casting (DCC), were analyzed by optical microscope, differential scanning calorimetry, transmission electron microscope and X ray diffraction. It is found that the surface and subsurface quality of the ingot is improved largely due to the absence of an ingot mold, which is impossible to achieve with conventional DCC. It is also found that the intense forced convection can promote the fast superheat evacuation and break the dendrite arms, leading to the grain multiplication and the appearance of a fine equiaxed grains over the whole cross section. As a result, the hardness of EMC specimens increases one time than that from DCC in the as cast state. Even though after the solid solution treatment and the artificial aging, the DCC ingot still can not get the same hardness as EMC ones.展开更多
The 1050 aluminum alloy strip was prepared by means of electromagnetic and ultrasonic cast rolling on the modified asymmetric twin roll caster, and then the aluminum substrate for presensitized plate was prepared thro...The 1050 aluminum alloy strip was prepared by means of electromagnetic and ultrasonic cast rolling on the modified asymmetric twin roll caster, and then the aluminum substrate for presensitized plate was prepared through cold rolling and annealing.The effects of electromagnetic and ultrasonic cast rolling on microstructure, mechanical properties, surface roughness and electrolytic corrosion properties of 1050 aluminum substrate were studied. The results show that electromagnetic and ultrasonic cast rolling can decrease the average crystallite size of aluminum substrate by 5 μm, increase the crystal boundaries with uniform distribution, and make the second-phase particles with smaller size distributed dispersively in the substrate, meanwhile, it can increase the tensile strength, elongation and micro-hardness by 4.58%, 9.85% and HV 2, respectively, reduce the surface roughness, make the surface appearance more even, electrolytic corrosion polarization curve of aluminum substrate more smooth and the surface corrosion pits with regular shape more dispersive.展开更多
The research and development status of casting magnesium alloys including the commercial casting alloys and the new types casting alloys are reviewed,with more attention to microstructure and mechanical properties of ...The research and development status of casting magnesium alloys including the commercial casting alloys and the new types casting alloys are reviewed,with more attention to microstructure and mechanical properties of modified-AZ91,AM60 and WE43 alloys with various additions,and new types of low cost casting alloys and high strength casting alloys.The modification and/or refinement of Mg2 Si phase in Mg-Al-Si based casting alloys by various additions are discussed and new purifying technologies for casting magnesium alloys are introduced to improve the performance.The modified AZ81 alloy with reduced impurities is found to have the tensile strength of 280 ± 6 MPa and elongation of 16% ± 0.7%.The fatigue strength of AZ91 D alloy could be obviously improved by addition of Ce and Nd.The Mg-16Gd-2Ag-0.3Zr alloy exhibits very high tensile and yield strengths(UTS:423 MPa and YS:328 MPa);however,its elongation still needs to be improved.展开更多
基金financially supported by the National Science Foundation of China(Grant No.51171053 and No.51471062)
文摘In the present research, microstructure refinement of a high-Nb TiAl alloy(Ti-48Al-8Nb-0.15B) was realized by means of the electromagnetic continuous casting(EMCC) technique. The microstructure of an ingot obtained by EMCC was analyzed using scanning electron microscopy(SEM). As compared with the raw as-cast al oy, the obtained EMCC alloy presented a much finer microstructure with lamellar colonies with a mean size of about 50-70 μm because the electromagnetic stirring broke initial dendrites and enhanced the heterogeneous nucleation. As the grains were refined, the properties of the TiAl alloy were improved significantly. This implies that the EMCC technique could offer the possibility of application for high-Nb TiAl alloys with a refined microstructure and excel ent properties to be used as a structural material.
基金financially supported by the National Key Technology R&D Program(No.2012BAF09B04)International Technical Cooperation Project(No.2011DFR50950)of the Ministry of Science and Technology of Chinathe Chongqing Science and Technology Commission(No.CSTC2013JCYJC60001)
文摘For the large magnesium alloy ingot, there is a considerable difference in cooling rate of different parts in the ingot, which leads to non-uniform distribution of the secondary phases, solute segregation and tensile properties. In the present research, an heavy AZ61 alloy ingot with a diameter of 500 mm was made by semi-continuous casting. The microstructure and mechanical properties at different positions along the radial direction of the large ingot were investigated by using an optical microscope(OM), a scanning electron microscope(SEM), an energy dispersive spectroscope(EDS), and a micro-hardness tester. The results indicate that the microstructure of the AZ61 ingot is non-uniform in different locations. It changes from equiaxed to columnar grains from the center to the edge; the average grain size gradually reduces from 1,005 μm to 763 μm, the secondary dendrite arm spacing reduces from 78 μm to 50 μm, and the Mg17(Al,Zn)12 phase is also refined. The micro-hardness value increases from 55.4 HV at the center to 72.5 HV at the edge of the ingot due to the microstructure differences, and the distribution of micro-hardness at the edge of the ingot is more uniform than that in the center. The tensile properties at room temperature show little difference from the center to the edge of the ingot except that the elongation at the edge is only 3.5%, much lower than that at other areas. The fracture mechanism is ductile fracture at the center and cleavage fracture at the edge of the ingot, and at the 1/2 radius of the ingot, a mixture of ductile and cleavage fracture is present.
基金This research was supported by Major State Basic Research Projects of China, Grant No.:G1999064905 and the National Natural Science Foundation of China, No.59974009.
文摘The relationship between electromagnetic frequency and microstructures of continuous casting aluminum alloys was studied. 7075 aluminum alloy ingot of 100 mm in diameter was produced by electromagnetic continuous casting process, the microstructures of as-cast ingot was examined by scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS). The results showed that electromagnetic frequency greatly influenced segregation and microstructures of as-cast ingot, and product quality can be guaranteed by the application of a proper frequency. Electromagnetic frequency plays a significant role in solute redistribution; low frequency is more efficient for promoting solution of alloying elements.
基金National "863" project (NO.2001AA332030) of China
文摘The super high strength aluminum alloy ingots with 100 mm in diameter were cast by the process of low-frequency electromagnetic horizontal continuous casting (LFEHC) and the effect of electromagnetic field on the as-cast microstructure was studied. Results show that microstructure of the sample prepared by the LFEHC process was greatly refined. Microstructures at the border and the center of the ingots were fine, uniform and rosette-shaped. Electromagnetic frequency plays a key role in microstructure refining. Fine and uniform microstructures can be obtained with optimal electromagnetic frequency. In this experiment, under a frequency of 30 Hz the microstructure was the finest and the most uniform.
基金supported by the Major State Basic Research Development Program of China (Nos. 2007CB613701 and 2007CB613702)the National Natural Science Foundation of China (Nos. 50904018, 51004032 and 50974037)+2 种基金the Program for New Century Excellent Talents in Chinese Universities (No. NCET-08-0098)the Fundamental Research Funds for the Central Universities of China (Nos. N090409002 and N090209002)the China Postdoctoral Science Foundation (No. 20100471468)
文摘AZ31 alloy billets of 200 mm in diameter were produced by three different processes of conventional direct chill (DC) casting, low-frequency electromagnetic casting (LFEC) and low-frequency electromagnetic vibration casting (LFEVC), respectively. The effect of LFEC and LFEVC on the microstructures, macmsegregation and mechanical properties of AZ31 alloy billets was investigated. In conventional DC casting, the AZ31 alloy billets exhibited coarse grains (about 370 μa) and severe segregation of A1 and Zn. In the presence of a solo low-frequency alternating magnetic field or a low-frequency electromagnetic vibration field applied during DC casting of Ф200 mm AZ31 billets, grains in the AZ31 alloy billets were effectively reffmed (about 210 μa) and the macrosegregation of A1 and Zn in the billets was greatly decreased. Furthermore, the tensile strength, fracture elongation and hardness of the as-cast AZ31 alloy billets were improved by the processes of LFEC and LFEVC relative to that cast by the process of conventional DC casting.
基金Projects(2007CB613701,2007CB613702)supported by the National Basic Research Program of ChinaProjects(50974037,50904018)supported by the National Natural Science Foundation of China+1 种基金Project(NCET-08-0098)supported by New Century Excellent Talents in University of ChinaProjects(N09040902,N090209002)supported by the Special Foundation for Basic Scientific Research of Central Colleges
文摘Under the high-intensity ultrasonic field,AZ80 magnesium alloy was semi-continuously cast.The effects of ultrasonic intensity on the as-cast microstructures and mechanical properties were investigated.The results show that the microstructures of the alloy cast under high-intensity ultrasonic field are fine and uniform,and the grains are equiaxed,rose-shaped or globular with an average size of 257μm.High-intensity field significantly decreases the grain size,changes the morphologies of theβ-Mg17Al12 phases and reduces their area fraction.It is also shown that a proper increase in ultrasonic intensity is helpful to obtain fine,uniform and equiaxed as-cast microstructures.The optimum ultrasonic parameters are that frequency is 20 kHz and ultrasonic intensity is 1 368 W.The mechanical tests show that the mechanical properties of the as-cast AZ80 magnesium alloy billets cast under ultrasonic field are greatly improved,and with increasing the ultrasonic intensity,the mechanical properties of the entire alloy billets are much higher and more uniform than those of the alloy without ultrasonic field.
文摘LY12 aluminum alloys made by electromagnetic casting (EMC) and direct chill casting (DCC), were analyzed by optical microscope, differential scanning calorimetry, transmission electron microscope and X ray diffraction. It is found that the surface and subsurface quality of the ingot is improved largely due to the absence of an ingot mold, which is impossible to achieve with conventional DCC. It is also found that the intense forced convection can promote the fast superheat evacuation and break the dendrite arms, leading to the grain multiplication and the appearance of a fine equiaxed grains over the whole cross section. As a result, the hardness of EMC specimens increases one time than that from DCC in the as cast state. Even though after the solid solution treatment and the artificial aging, the DCC ingot still can not get the same hardness as EMC ones.
基金Project(2014CB046702) supported by the National Basic Research Program of ChinaProject supported by the Postdoctoral Science Foundation of Central South University,China
文摘The 1050 aluminum alloy strip was prepared by means of electromagnetic and ultrasonic cast rolling on the modified asymmetric twin roll caster, and then the aluminum substrate for presensitized plate was prepared through cold rolling and annealing.The effects of electromagnetic and ultrasonic cast rolling on microstructure, mechanical properties, surface roughness and electrolytic corrosion properties of 1050 aluminum substrate were studied. The results show that electromagnetic and ultrasonic cast rolling can decrease the average crystallite size of aluminum substrate by 5 μm, increase the crystal boundaries with uniform distribution, and make the second-phase particles with smaller size distributed dispersively in the substrate, meanwhile, it can increase the tensile strength, elongation and micro-hardness by 4.58%, 9.85% and HV 2, respectively, reduce the surface roughness, make the surface appearance more even, electrolytic corrosion polarization curve of aluminum substrate more smooth and the surface corrosion pits with regular shape more dispersive.
基金supported by the National Natural Science Foundation of China(Grant Nos.51531002,51474043 and 51571043)the Ministry of Education of China(SRFDR 20130191110018)+1 种基金Chongqing Municipal Government(CSTC2013JCYJC60001,CEC project,Two River Scholar Project and The Chief Scientist Studio Project)Fundamental Research Funds for the Central Universities(No.106112015CDJZR135515)
文摘The research and development status of casting magnesium alloys including the commercial casting alloys and the new types casting alloys are reviewed,with more attention to microstructure and mechanical properties of modified-AZ91,AM60 and WE43 alloys with various additions,and new types of low cost casting alloys and high strength casting alloys.The modification and/or refinement of Mg2 Si phase in Mg-Al-Si based casting alloys by various additions are discussed and new purifying technologies for casting magnesium alloys are introduced to improve the performance.The modified AZ81 alloy with reduced impurities is found to have the tensile strength of 280 ± 6 MPa and elongation of 16% ± 0.7%.The fatigue strength of AZ91 D alloy could be obviously improved by addition of Ce and Nd.The Mg-16Gd-2Ag-0.3Zr alloy exhibits very high tensile and yield strengths(UTS:423 MPa and YS:328 MPa);however,its elongation still needs to be improved.