A series of Al-6Si-3Cu-(0.3-2)Mg alloys were produced by a conventional casting process.Cooling slope technique wasemployed to produce feedstocks before they were thixoformed at50%liquid fraction.The effect of Mg on t...A series of Al-6Si-3Cu-(0.3-2)Mg alloys were produced by a conventional casting process.Cooling slope technique wasemployed to produce feedstocks before they were thixoformed at50%liquid fraction.The effect of Mg on the microstructure ofAl-Si-Cu aluminium alloys under as-cast and semisolid conditions was investigated.It was found that by adding Mg to Al-Si-Cualloy,some of the Al2Cu phase and silicon were consumed to form Al5Cu2Mg3Si5and Mg2Si phases.The needle-likeβ-Al5FeSi phasetransformed to Chinese-script-likeπ-Al8Mg3FeSi6with the addition of Mg.In the as-cast alloys,the primaryα(Al)was dendritic,butas the Mg content increased,the phase became less dendritic.Moreover,the Mg addition considerably modified the size of theα(Al)phase,but it had no significant effect on the silicon morphology.In the thixoformed alloys,the microstructure showed a fine globularprimary phase surrounded by uniformly distributed silicon and fragmented intermetallic phases.The eutectic silicon was modifiedfrom a flaky and acicular shape to fine fibrous particles.The effect of Mg on eutectic silicon during semisolid processing wasevident.The primary Mg2Si particles were modified from big polygonal particles to become smaller and more globular,whereas themorphology of the Chinese-script-likeπ-Al8Mg3FeSi6changed to a compact shape.The results also exhibit that as the Mg content inthe A319alloy increased,the hardness,yield strength and ultimate tensile strength of the thixoformed alloys significantly improved,but the elongation to fracture dropped.展开更多
As a new attempt to recycle minute metal scraps, the possibility of manufacturing design materials by semisolid extrusion processing was shown.A design material with an intended shape, such as a character or petal sha...As a new attempt to recycle minute metal scraps, the possibility of manufacturing design materials by semisolid extrusion processing was shown.A design material with an intended shape, such as a character or petal shape, was manufactured using minute metal scraps.Similarly, a design material with an intended color pattern for each metal, such as red copper in a white aluminum matrix, resembling grainlike wood, was manufactured by mixing two or more types of minute metal scrap.In addition, secondary design materials, which have engraved patterns on the surface of the target metal made by an electric discharge machine using the above primary design material as an electrode, were manufactured.展开更多
Semisolid processing is now a commercially successful manufacturing route to produce net-shape parts in automotive industry. The conspicuous results of alloy optimization with thermodynamic simulations for semisolid p...Semisolid processing is now a commercially successful manufacturing route to produce net-shape parts in automotive industry. The conspicuous results of alloy optimization with thermodynamic simulations for semisolid processing of commercial AM60 alloy were present. The results indicate that the available processing temperature range of AM60 alloy is 170 ℃. The temperature sensitivity of solid fraction decreases with increasing solid fraction or with decreasing temperature above eutectic reaction temperature of AM60 alloy. When the solid fraction φs is 0.4, corresponding processing temperature is 603.8 ℃ and the sensitivity -dφs/dT is 0.0184. The effects of various alloying elements on the solidification behavior and SSM processability of AM60 alloy were calculated with Pandat software.展开更多
The mechanical properties of Ti−Cu alloys processed via thixoforming were evaluated.Ti−Cu(25,27,and 29 wt.%Cu)ingots were produced via arc melting,homogenization at 950℃ for 24 h,and hot-forging at 900℃,followed by ...The mechanical properties of Ti−Cu alloys processed via thixoforming were evaluated.Ti−Cu(25,27,and 29 wt.%Cu)ingots were produced via arc melting,homogenization at 950℃ for 24 h,and hot-forging at 900℃,followed by thixoforming at a speed of 8 mm/s after isothermal heat treatment at 1035℃ for 300 s.The thixoformed alloys exhibited good mechanical strength,limited plasticity under tensile loading,and reasonable plasticity under compressive loading.The mechanical strength and plasticity decreased as the Cu content increased as a result of the increasing volume fraction of the peritectic Ti_(2)Cu phase(transformed liquid),which exhibited a lower strength and plasticity than theα+Ti_(2)Cu regions(transformed solid).These findings indicated that the trade-off between the mechanical properties and semisolid processability is largely governed by the Cu content.展开更多
The mold-filling ability of the semisolid alloy has very important effects onthe quality and properties of the work pieces produced by the semisolid forming process. Thefactorial experiments show that all of the heati...The mold-filling ability of the semisolid alloy has very important effects onthe quality and properties of the work pieces produced by the semisolid forming process. Thefactorial experiments show that all of the heating factors, such as mold temperature, heatingtemperature and the keeping time of billets, have some effects on the mold-filling ability ofsemisolid alloy. According to the analysis of influencing extent on the filling ability, it is foundthat the most important one of the factors is the mold temperature instead of the billetstemperature, the next one is the heating temperature of the billet, and the keeping time rows on thethird. It is also found that there is an interrelation between the billet heating temperature andthe mold temperature. The effect of the interrelation on the mold-filling ability is even strongerthan the keeping time. The higher the mold temperature, heating temperature or the keeping time is,the better the mold-filling ability of the semisolid alloy is. The parameter to describe themold-filling ability, defined as the maximum filling height along the uptight direction or themaximum filling length along the horizontal direction, can be theoretically determined according tothe flowing theory of viscous fluid.展开更多
To investigate the possibility of substituting the mechanical stirring system with electromagnetic stirring (EMS) system for aluminum rheo die-casting, the EMS under the different stirring cooling conditions was carri...To investigate the possibility of substituting the mechanical stirring system with electromagnetic stirring (EMS) system for aluminum rheo die-casting, the EMS under the different stirring cooling conditions was carried out. It was found that in the early period of solidification, the dendrite breakages led to a fine primary phase. When dendrites grew coarsely, the effect of ripening on grain size overwhelmed that of dendrite breakage. It was also found that the high cooling rate favored large nucleation rate, and led to a fine primary phase. But high cooling rate also made the growth rate of the dendrite arm, which prevented the dendrite arm from being sheared off. Therefore there were a suitable stirring time and suitable cooling rate to obtain the best rheo die-casting structure. Qualified semisolid A356 aluminum alloy was successfully manufactured with short time EMS.展开更多
In this paper, a novel near-net-shape forming process, continuous semisolid extrusion process （CSEP） of AZ31 alloy was proposed, and the dynamical solidification behaviors and metal flow during the process were firs...In this paper, a novel near-net-shape forming process, continuous semisolid extrusion process （CSEP） of AZ31 alloy was proposed, and the dynamical solidification behaviors and metal flow during the process were firstly investigated. During casting AZ31 alloy by this process, non-uniform microstructure distributions and non- equilibrium solidification region near the roll surface were found in the roll-shoe gap. Microstructural evolution from dendrite to rosette and spherical grains was observed during the casting by CSEP. Casting temperature, roll-shoe gap width and cooling ability have great effect on casting process and metal flow, so these factors should be carefully controlled, a proper casting temperature of 710-750℃ is suggested. The white α phases were strongly stretched during the processing, and the remnant liquids are correspondingly distributes along the solid phase boundaries and also show stripped lines.展开更多
The effect of solid-solution-treatment on the semisolid microstructure of Zn-22Al with developed dendrites was investigated. Forming Zn-22Al products by semisolid metal processing offers significant advantages, such a...The effect of solid-solution-treatment on the semisolid microstructure of Zn-22Al with developed dendrites was investigated. Forming Zn-22Al products by semisolid metal processing offers significant advantages, such as reductions in macro-segregation, porosity and forming costs. Thermal and rnicrostructural analyses of the formed Zn-22Al alloy were performed by differential scanning calorimetry, scanning electron microscopy and optical microscopy. The changes in the microstructures and phase transformation in response to various solid- solution-treatments were analysed. In this study, as-cast samples were held isothermally at 330 ℃ for 0.5- 5 h and then partially remelted at a semisolid temperature of 438 ℃ for 1 h to produce a solid-globular grain structure in a liquid matrix. A non-dendritic semisolid microstructure could not be obtained when the traditionally cast Zn 22Al alloy with developed dendrites was subjected directly to partial remelting. After solid-solution-treatment at 330 ℃, the black interdendritic eutectics were dissolved, and the dendritic structures gradually transformed into uniform β structures when the treatment time was increased. The coarsened and merged dendrites were separated as a result of penetration by the liquid phase and melting of the residual eutectic at sites along the former grain boundaries. The microstructure of the solid-solution- treated sample transformed into a small globular structure; the best shape factor of 0.9, corresponding to a particle size of 40 ± 16 μm, is achieved when the sample was treated for 3 h followed by direct partial remelting into its semisolid zone.展开更多
Thixoforming is a processing method that deforms metal in a semisolid state.The advantages of this process include the production of parts with good surface finish,fine microstructures and superior mechanical properti...Thixoforming is a processing method that deforms metal in a semisolid state.The advantages of this process include the production of parts with good surface finish,fine microstructures and superior mechanical properties.However,the process mostly produces parts from aluminium cast grades,thereby not fully utilising the true potential of this method.Hence,thermodynamic modelling can be used to formulate alloy compositions that favour this processing method.Here,the effects of reducing copper content and increasing silicon and magnesium contents on the thixoformability of aluminium alloy 2014 were presented.The work consists of both the modelling and experimental validation.Results showed that by increasing Si and decreasing Cu content in the alloy,the solidification interval temperature was decreased and the temperature working window between the stipulated liquid fractions was widened,two of the characteristics favouring the process.A high solid-solution temperature employed resulted in the dissolution of unfavourable Mg2Si compound.An increase in Mg content used also resulted in the formation of the compactπ-Al8FeMg3Si6 phase and the decrease in the amount of the sharp and plate-like structure of theβ-Al5FeSi phase,improving the strength of the modified alloy.Subsequent T6 heat treatment successfully further increased the strength of the modified alloy.展开更多
The rheo-squeeze casting(RSC)process is a newly-developed casting process for high-performance components.In order to further improve the mechanical properties of magnesium alloys,AZ91-2wt.%Ca(AZX912)alloy was prepare...The rheo-squeeze casting(RSC)process is a newly-developed casting process for high-performance components.In order to further improve the mechanical properties of magnesium alloys,AZ91-2wt.%Ca(AZX912)alloy was prepared by the RSC process and then subjected to heat treatment.The microstructure evolution and mechanical properties of AZX912 alloy during heat treatment were investigated.It was found that during solid solution treatment at 410°C,β-Mg_(17)Al_(12) phase with low melting point dissolves intoα-Mg matrix,while the connected network-like Al_2Ca phase with high melting point tends to separate gradually,and the tips of Al_2Ca phase is partially spheroidized.With the increase of solid solution time,the yield strength(YS)of AZX912 alloy decreases gradually while the ultimate tensile strength(UTS)and elongation to failure(E_f)increase continuously.Isothermal ageing at 225°C promotes the precipitation ofβ-Mg_(17)Al_(12) phase in the matrix of AZX912 alloy.The hardness reaches the peak after ageing for 96 h and the increase in hardness is about 24.8%.The precipitation ofβ-Mg_(17)Al_(12) phase during ageing treatment is beneficial to YS but harmful to E_f.The mechanism of microstructure evolution during heat treatment and its effect on mechanical properties are discussed.展开更多
The effects of Al-8B grain refiner on microstructure and tensile properties of an Al-12Zn-3Mg-2.5Cu alloy produced by modified strain induced melt activation process were investigated. Pre-deformation of 60% was used ...The effects of Al-8B grain refiner on microstructure and tensile properties of an Al-12Zn-3Mg-2.5Cu alloy produced by modified strain induced melt activation process were investigated. Pre-deformation of 60% was used by hot working at 300 ℃. After pre-deformation, the samples were heated to a temperature above the solidus and below the liquidus point and maintained in the isothermal conditions at three different temperatures（500, 550 and 590 ℃） for varying time（10, 20 and 40 min）. It was observed that strain induced melt activation has caused the globular morphology of α（Al） grains. Microstructural study was carried out on the alloy by using optical microscope and scanning electron microscope in both unrefined and B-refined conditions. The results showed that for the desired microstructures of the alloy during SIMA process, the optimum temperature and time are 550 ℃ and 10 min, respectively. After the T6 heat treatment, the average tensile strengths increased from 278 to 585 MPa and 252 to 560 MPa for samples refined with 3.75% Al-8B before and after SIMA process, respectively. The ultimate strength of SIMA specimens is lower than that of B-refined specimens.展开更多
The billets of AM60 alloy, prepared with self-inoculation method, were partially remelted into semisolid state. Effects of process parameters on remelting microstructure of semisolid billet were investigated. Experime...The billets of AM60 alloy, prepared with self-inoculation method, were partially remelted into semisolid state. Effects of process parameters on remelting microstructure of semisolid billet were investigated. Experimental results show that the solid particles obtained with self-inoculation method are in smaller grain size and globular shape after partial remelting, compared with those prepared with other casting methods. In the optimized process conditions, the average size of solid particles of partially remelted billet is 65 μm, and the shape factor is 1.12. The process parameters, i.e. pouting temperature, addition amount of self-inoculants, and the slope angle of multi-stream mixing cooling chalmel have influence on the microstructure of partially remelted billet. The optimized temperature is from 680 ℃ to 700 ℃, addition amount of self-inoculants is between 5% and 7% （mass fraction）, slope angle of multi-stream mixing cooling channel is between 30° and 45°, with which the dendritic microstructure of as-cast billet can be avoided, and the size of solid particles ofremelted billet is reduced.展开更多
Two kinds of bi-metal composite parts （Sn-15%Pb and Pb-22%Sn bi-metal system, and Al-7%Si and SiCp/6061 MMC bi-metal system） were prepared by the strain-induced melt activated thixo-forging. The interfaces of the bi...Two kinds of bi-metal composite parts （Sn-15%Pb and Pb-22%Sn bi-metal system, and Al-7%Si and SiCp/6061 MMC bi-metal system） were prepared by the strain-induced melt activated thixo-forging. The interfaces of the bi-metal composites were observed by OM and SEM. The observations show that the semisolid metals keep independence during thixo-forging. The solid phases in the semisolid slurries maintain their original morphologies after thixo-forging. The liquid phases near the interface mix together and form a thin layer. The interfaces are bonded firmly with the metallurgical bonding. No oxide layers are found at the interfaces. Strengths of the interfaces were investigated by the micro-hardness test. The experimental results show that the composite interfaces have high strength. However, the agglomerated enhancing particles cause fine defect on the interface of the Al-7%Si and SiCr/6061 MMC bi-metal composite.展开更多
基金Universiti Kebangsaan Malaysia(UKM)and the Ministry of Higher Education(MOHE),Malaysia,for financial support under research grants AP-2012-014 and FRGS/1/2014/TK01/UKM/01/2
文摘A series of Al-6Si-3Cu-(0.3-2)Mg alloys were produced by a conventional casting process.Cooling slope technique wasemployed to produce feedstocks before they were thixoformed at50%liquid fraction.The effect of Mg on the microstructure ofAl-Si-Cu aluminium alloys under as-cast and semisolid conditions was investigated.It was found that by adding Mg to Al-Si-Cualloy,some of the Al2Cu phase and silicon were consumed to form Al5Cu2Mg3Si5and Mg2Si phases.The needle-likeβ-Al5FeSi phasetransformed to Chinese-script-likeπ-Al8Mg3FeSi6with the addition of Mg.In the as-cast alloys,the primaryα(Al)was dendritic,butas the Mg content increased,the phase became less dendritic.Moreover,the Mg addition considerably modified the size of theα(Al)phase,but it had no significant effect on the silicon morphology.In the thixoformed alloys,the microstructure showed a fine globularprimary phase surrounded by uniformly distributed silicon and fragmented intermetallic phases.The eutectic silicon was modifiedfrom a flaky and acicular shape to fine fibrous particles.The effect of Mg on eutectic silicon during semisolid processing wasevident.The primary Mg2Si particles were modified from big polygonal particles to become smaller and more globular,whereas themorphology of the Chinese-script-likeπ-Al8Mg3FeSi6changed to a compact shape.The results also exhibit that as the Mg content inthe A319alloy increased,the hardness,yield strength and ultimate tensile strength of the thixoformed alloys significantly improved,but the elongation to fracture dropped.
文摘As a new attempt to recycle minute metal scraps, the possibility of manufacturing design materials by semisolid extrusion processing was shown.A design material with an intended shape, such as a character or petal shape, was manufactured using minute metal scraps.Similarly, a design material with an intended color pattern for each metal, such as red copper in a white aluminum matrix, resembling grainlike wood, was manufactured by mixing two or more types of minute metal scrap.In addition, secondary design materials, which have engraved patterns on the surface of the target metal made by an electric discharge machine using the above primary design material as an electrode, were manufactured.
基金Project(50964010) supported by the National Natural Science Foundation of ChinaProject(090WCGA894) supported by the International S&T Cooperation Program of Gansu Province,China
文摘Semisolid processing is now a commercially successful manufacturing route to produce net-shape parts in automotive industry. The conspicuous results of alloy optimization with thermodynamic simulations for semisolid processing of commercial AM60 alloy were present. The results indicate that the available processing temperature range of AM60 alloy is 170 ℃. The temperature sensitivity of solid fraction decreases with increasing solid fraction or with decreasing temperature above eutectic reaction temperature of AM60 alloy. When the solid fraction φs is 0.4, corresponding processing temperature is 603.8 ℃ and the sensitivity -dφs/dT is 0.0184. The effects of various alloying elements on the solidification behavior and SSM processability of AM60 alloy were calculated with Pandat software.
基金the Brazilian research funding agencies FAPESP(São Paulo Research Foundation)under the grant numbers 2013/24786-3 and 2017/07040-9CAPES(Federal Agency for the Support and Improvement of Higher Education).
文摘The mechanical properties of Ti−Cu alloys processed via thixoforming were evaluated.Ti−Cu(25,27,and 29 wt.%Cu)ingots were produced via arc melting,homogenization at 950℃ for 24 h,and hot-forging at 900℃,followed by thixoforming at a speed of 8 mm/s after isothermal heat treatment at 1035℃ for 300 s.The thixoformed alloys exhibited good mechanical strength,limited plasticity under tensile loading,and reasonable plasticity under compressive loading.The mechanical strength and plasticity decreased as the Cu content increased as a result of the increasing volume fraction of the peritectic Ti_(2)Cu phase(transformed liquid),which exhibited a lower strength and plasticity than theα+Ti_(2)Cu regions(transformed solid).These findings indicated that the trade-off between the mechanical properties and semisolid processability is largely governed by the Cu content.
文摘The mold-filling ability of the semisolid alloy has very important effects onthe quality and properties of the work pieces produced by the semisolid forming process. Thefactorial experiments show that all of the heating factors, such as mold temperature, heatingtemperature and the keeping time of billets, have some effects on the mold-filling ability ofsemisolid alloy. According to the analysis of influencing extent on the filling ability, it is foundthat the most important one of the factors is the mold temperature instead of the billetstemperature, the next one is the heating temperature of the billet, and the keeping time rows on thethird. It is also found that there is an interrelation between the billet heating temperature andthe mold temperature. The effect of the interrelation on the mold-filling ability is even strongerthan the keeping time. The higher the mold temperature, heating temperature or the keeping time is,the better the mold-filling ability of the semisolid alloy is. The parameter to describe themold-filling ability, defined as the maximum filling height along the uptight direction or themaximum filling length along the horizontal direction, can be theoretically determined according tothe flowing theory of viscous fluid.
文摘To investigate the possibility of substituting the mechanical stirring system with electromagnetic stirring (EMS) system for aluminum rheo die-casting, the EMS under the different stirring cooling conditions was carried out. It was found that in the early period of solidification, the dendrite breakages led to a fine primary phase. When dendrites grew coarsely, the effect of ripening on grain size overwhelmed that of dendrite breakage. It was also found that the high cooling rate favored large nucleation rate, and led to a fine primary phase. But high cooling rate also made the growth rate of the dendrite arm, which prevented the dendrite arm from being sheared off. Therefore there were a suitable stirring time and suitable cooling rate to obtain the best rheo die-casting structure. Qualified semisolid A356 aluminum alloy was successfully manufactured with short time EMS.
基金supports from National High-Tech R&D Program of China (GrantNo. 2007AA03Z111)Natural Science Foundation of China (Grant No. 50604007)the Program for New Century Excellent Talents in University (Grant No.NCET-06-0285 and NCET-08-0097)
文摘In this paper, a novel near-net-shape forming process, continuous semisolid extrusion process （CSEP） of AZ31 alloy was proposed, and the dynamical solidification behaviors and metal flow during the process were firstly investigated. During casting AZ31 alloy by this process, non-uniform microstructure distributions and non- equilibrium solidification region near the roll surface were found in the roll-shoe gap. Microstructural evolution from dendrite to rosette and spherical grains was observed during the casting by CSEP. Casting temperature, roll-shoe gap width and cooling ability have great effect on casting process and metal flow, so these factors should be carefully controlled, a proper casting temperature of 710-750℃ is suggested. The white α phases were strongly stretched during the processing, and the remnant liquids are correspondingly distributes along the solid phase boundaries and also show stripped lines.
基金the Ministry of Science, Technology and Innovation(MOSTI)Malaysia for sponsoring this study under Grant 03-0 1-02-SF0047
文摘The effect of solid-solution-treatment on the semisolid microstructure of Zn-22Al with developed dendrites was investigated. Forming Zn-22Al products by semisolid metal processing offers significant advantages, such as reductions in macro-segregation, porosity and forming costs. Thermal and rnicrostructural analyses of the formed Zn-22Al alloy were performed by differential scanning calorimetry, scanning electron microscopy and optical microscopy. The changes in the microstructures and phase transformation in response to various solid- solution-treatments were analysed. In this study, as-cast samples were held isothermally at 330 ℃ for 0.5- 5 h and then partially remelted at a semisolid temperature of 438 ℃ for 1 h to produce a solid-globular grain structure in a liquid matrix. A non-dendritic semisolid microstructure could not be obtained when the traditionally cast Zn 22Al alloy with developed dendrites was subjected directly to partial remelting. After solid-solution-treatment at 330 ℃, the black interdendritic eutectics were dissolved, and the dendritic structures gradually transformed into uniform β structures when the treatment time was increased. The coarsened and merged dendrites were separated as a result of penetration by the liquid phase and melting of the residual eutectic at sites along the former grain boundaries. The microstructure of the solid-solution- treated sample transformed into a small globular structure; the best shape factor of 0.9, corresponding to a particle size of 40 ± 16 μm, is achieved when the sample was treated for 3 h followed by direct partial remelting into its semisolid zone.
基金the National University of Malaysia (Universiti Kebangsaan Malaysia, UKM)the Ministry of Education (MOE) of Malaysia for the financial support received under research grant DIP-2016-007
文摘Thixoforming is a processing method that deforms metal in a semisolid state.The advantages of this process include the production of parts with good surface finish,fine microstructures and superior mechanical properties.However,the process mostly produces parts from aluminium cast grades,thereby not fully utilising the true potential of this method.Hence,thermodynamic modelling can be used to formulate alloy compositions that favour this processing method.Here,the effects of reducing copper content and increasing silicon and magnesium contents on the thixoformability of aluminium alloy 2014 were presented.The work consists of both the modelling and experimental validation.Results showed that by increasing Si and decreasing Cu content in the alloy,the solidification interval temperature was decreased and the temperature working window between the stipulated liquid fractions was widened,two of the characteristics favouring the process.A high solid-solution temperature employed resulted in the dissolution of unfavourable Mg2Si compound.An increase in Mg content used also resulted in the formation of the compactπ-Al8FeMg3Si6 phase and the decrease in the amount of the sharp and plate-like structure of theβ-Al5FeSi phase,improving the strength of the modified alloy.Subsequent T6 heat treatment successfully further increased the strength of the modified alloy.
基金financially supported by National Natural Science Foundation of China(No.51601076 and No.51401093)Natural Science Fund for Colleges and Universities in Jiangsu Province(No.16KJB430013)
文摘The rheo-squeeze casting(RSC)process is a newly-developed casting process for high-performance components.In order to further improve the mechanical properties of magnesium alloys,AZ91-2wt.%Ca(AZX912)alloy was prepared by the RSC process and then subjected to heat treatment.The microstructure evolution and mechanical properties of AZX912 alloy during heat treatment were investigated.It was found that during solid solution treatment at 410°C,β-Mg_(17)Al_(12) phase with low melting point dissolves intoα-Mg matrix,while the connected network-like Al_2Ca phase with high melting point tends to separate gradually,and the tips of Al_2Ca phase is partially spheroidized.With the increase of solid solution time,the yield strength(YS)of AZX912 alloy decreases gradually while the ultimate tensile strength(UTS)and elongation to failure(E_f)increase continuously.Isothermal ageing at 225°C promotes the precipitation ofβ-Mg_(17)Al_(12) phase in the matrix of AZX912 alloy.The hardness reaches the peak after ageing for 96 h and the increase in hardness is about 24.8%.The precipitation ofβ-Mg_(17)Al_(12) phase during ageing treatment is beneficial to YS but harmful to E_f.The mechanism of microstructure evolution during heat treatment and its effect on mechanical properties are discussed.
文摘The effects of Al-8B grain refiner on microstructure and tensile properties of an Al-12Zn-3Mg-2.5Cu alloy produced by modified strain induced melt activation process were investigated. Pre-deformation of 60% was used by hot working at 300 ℃. After pre-deformation, the samples were heated to a temperature above the solidus and below the liquidus point and maintained in the isothermal conditions at three different temperatures（500, 550 and 590 ℃） for varying time（10, 20 and 40 min）. It was observed that strain induced melt activation has caused the globular morphology of α（Al） grains. Microstructural study was carried out on the alloy by using optical microscope and scanning electron microscope in both unrefined and B-refined conditions. The results showed that for the desired microstructures of the alloy during SIMA process, the optimum temperature and time are 550 ℃ and 10 min, respectively. After the T6 heat treatment, the average tensile strengths increased from 278 to 585 MPa and 252 to 560 MPa for samples refined with 3.75% Al-8B before and after SIMA process, respectively. The ultimate strength of SIMA specimens is lower than that of B-refined specimens.
基金Project(2007CB613700) supported by the National Basic Research Program of ChinaProject(50964010) supported by the National Natural Science Foundation of ChinaProject(090WCGA894) supported by the International S&T Cooperation Program of Gansu Province,China
文摘The billets of AM60 alloy, prepared with self-inoculation method, were partially remelted into semisolid state. Effects of process parameters on remelting microstructure of semisolid billet were investigated. Experimental results show that the solid particles obtained with self-inoculation method are in smaller grain size and globular shape after partial remelting, compared with those prepared with other casting methods. In the optimized process conditions, the average size of solid particles of partially remelted billet is 65 μm, and the shape factor is 1.12. The process parameters, i.e. pouting temperature, addition amount of self-inoculants, and the slope angle of multi-stream mixing cooling chalmel have influence on the microstructure of partially remelted billet. The optimized temperature is from 680 ℃ to 700 ℃, addition amount of self-inoculants is between 5% and 7% （mass fraction）, slope angle of multi-stream mixing cooling channel is between 30° and 45°, with which the dendritic microstructure of as-cast billet can be avoided, and the size of solid particles ofremelted billet is reduced.
基金Project(1343-71333000469) supported by the Funding of Graduate Student Training of Central South University,China
文摘Two kinds of bi-metal composite parts （Sn-15%Pb and Pb-22%Sn bi-metal system, and Al-7%Si and SiCp/6061 MMC bi-metal system） were prepared by the strain-induced melt activated thixo-forging. The interfaces of the bi-metal composites were observed by OM and SEM. The observations show that the semisolid metals keep independence during thixo-forging. The solid phases in the semisolid slurries maintain their original morphologies after thixo-forging. The liquid phases near the interface mix together and form a thin layer. The interfaces are bonded firmly with the metallurgical bonding. No oxide layers are found at the interfaces. Strengths of the interfaces were investigated by the micro-hardness test. The experimental results show that the composite interfaces have high strength. However, the agglomerated enhancing particles cause fine defect on the interface of the Al-7%Si and SiCr/6061 MMC bi-metal composite.
