For the compromise of mechanical properties and product cost, the end-chilled sand casting technique was applied to studying the microstructure evolution of A356 Al alloy with cooling rate and the effect of different ...For the compromise of mechanical properties and product cost, the end-chilled sand casting technique was applied to studying the microstructure evolution of A356 Al alloy with cooling rate and the effect of different as-cast microstructures on the subsequent solution-treatment process. The experimental results show that the secondary dendrite arm spacing (SDAS) of primaryα(Al), the size of eutectic Si and the volume fraction of Al?Si eutectic are reduced with increasing the cooling rate. Eutectic Si, subjected to solution treatment at 540 °C for 1 h followed by water quenching to room temperature, is completely spheroidized at cooling rate of 2.6 K/s; is partially spheroidized atcooling rate of 0.6 K/s; and is only edge-rounded at cooling rates of 0.22 and 0.12 K /s. Whilst the microhardness is also the maximum at cooling rate of 2.6 K/s. It consequently suggests that subjected to modification by high cooling rate, the eutectic Si is more readily modified, thus shortening the necessary solution time at given solution temperature, i.e., reducing the product cost.展开更多
In order to decrease the metallurgical porosity and keyhole-induced porosity during deep penetration laser welding of Al and its alloys, and increase the mechanical properties of work-piece, the effects of welding par...In order to decrease the metallurgical porosity and keyhole-induced porosity during deep penetration laser welding of Al and its alloys, and increase the mechanical properties of work-piece, the effects of welding parameters such as laser power, welding speed and defocusing value on both kinds of porosities were systemically analyzed respectively, and the shape and fluctuation of plume of the keyhole were observed to reflect the stability of the keyhole. The results show that increasing laser power or decreasing laser spot size can lead to the rising of both number and occupied area of pores in the weld; meanwhile, the plume fluctuates violently over the keyhole, which is always companied with the intense metallic vapor, liquid metal spatter and collapsing in the keyhole, thus more pores are generated in the weld. The porosity in the weld reaches the minimum at welding velocity of 2.0 m/min when laser power is 5 kW and defocusing value is 0.展开更多
The semi-solid slurry of an A356 Al alloy, which was grain-fined by yttrium, was manufactured by low temperature pouring, The effects of grain-refining on the morphology and the grain size of the primary α phase in t...The semi-solid slurry of an A356 Al alloy, which was grain-fined by yttrium, was manufactured by low temperature pouring, The effects of grain-refining on the morphology and the grain size of the primary α phase in the semi-solid A356 Al alloy were researched. The results indicate that the semi-solid A356 AI alloy with particle-like and rosette-like primary α-Al can be prepared by low temperature pouring from a liquid grain-refined A356 alloy. The grain size and particle morphology of primary α-Al in the A356 Al alloy are markedly improved by the addition of 0.5 wt,% Y. The fining mechanism of Y on the morphology and grain size of the primary α-Al in the semi-solid A356 Al alloy was delved.展开更多
The semi-solid slurry of a hypoeutectic Al-Si alloy was manufactured by low superheat pouring and weak electromagnetic stirring. The effects of pouting temperature and stirring power on the semi-solid slurry were inve...The semi-solid slurry of a hypoeutectic Al-Si alloy was manufactured by low superheat pouring and weak electromagnetic stirring. The effects of pouting temperature and stirring power on the semi-solid slurry were investigated. The results indicated that the semi-solid slurry to satisfy rheocasting can be manufactured by low superheat pouring and weak electromagnetic stirring. The pouring temperature （or superheat） and the stirring power remarkably affected the morphology of primary α-Al and the size of primary α-Al, and there is no obvious effect of stirring time on primary α-Al. Compared with the samples made by low superheat pouring with no stirring, the nucleation rate, particle morphology and grain size of primary α-Al in A356 were markedly improved by low superheat pouring and weak electromagnetic stirring. On the condition of weak electromagnetic stirring, the pouring temperature with low superheat can be suitably raised to reach the effectiveness obtained from the lower pouring temperature without stirring.展开更多
A new method (liquidus casting) was used for 356 Al alloy semi-solid slurry making. The structures of 356 Al alloy cast by a Fe mould and semi-continuous casting machine at different temperatures were investigated. Ho...A new method (liquidus casting) was used for 356 Al alloy semi-solid slurry making. The structures of 356 Al alloy cast by a Fe mould and semi-continuous casting machine at different temperatures were investigated. How the globular grains form was also discussed. The results show that either being cast by single Fe mould or semi-continuous machine, the micro structures are not conventional dendrites but fine and net-globular grains. The average gram size is smaller than 30μm and suitable enough for thixoforming, meanwhile it can improve the mechanical properties of following products. Under the suitable casting velocity and cooling intensity, most of global grains prolong their global growth and collide with each other before dendritic growth because of the large amount of the nucleation sites.展开更多
Computer modeling of semi-solid structure formation is of significance in both understanding the mechanisms of globular structure formation and determining the effect of solidification conditions on final microstructu...Computer modeling of semi-solid structure formation is of significance in both understanding the mechanisms of globular structure formation and determining the effect of solidification conditions on final microstructure.A modified cellular automaton(mCA) model has been developed,which is coupled with macroscopic models for heat transfer calculation and microscopic models for nucleation and grain growth.The mCA model is applied to A356 Al alloy-one of the most widely used semi-solid alloys,to predict grain morphology and grain size during semi-solid solidification,and determines the effects of pouring temperature on the final microstructure.The modeling results show that the lower the initial temperature,the finer grain size will be obtained.In addition,the model can be used to predict the solutal micro-segregation.展开更多
基金Project(2011CB610403)support by the National Basic Research Program of ChinaProjects(51134011,51431008)supported by the National Natural Science Foundation of China+1 种基金Project(JC20120223)supported by the Fundamental Research Fund of Northwestern Polytechnical University,ChinaProject(51125002)supported by the National Funds for Distinguished Young Scientists of China
文摘For the compromise of mechanical properties and product cost, the end-chilled sand casting technique was applied to studying the microstructure evolution of A356 Al alloy with cooling rate and the effect of different as-cast microstructures on the subsequent solution-treatment process. The experimental results show that the secondary dendrite arm spacing (SDAS) of primaryα(Al), the size of eutectic Si and the volume fraction of Al?Si eutectic are reduced with increasing the cooling rate. Eutectic Si, subjected to solution treatment at 540 °C for 1 h followed by water quenching to room temperature, is completely spheroidized at cooling rate of 2.6 K/s; is partially spheroidized atcooling rate of 0.6 K/s; and is only edge-rounded at cooling rates of 0.22 and 0.12 K /s. Whilst the microhardness is also the maximum at cooling rate of 2.6 K/s. It consequently suggests that subjected to modification by high cooling rate, the eutectic Si is more readily modified, thus shortening the necessary solution time at given solution temperature, i.e., reducing the product cost.
基金Project(51204109)supported by the National Natural Science Foundation of China
文摘In order to decrease the metallurgical porosity and keyhole-induced porosity during deep penetration laser welding of Al and its alloys, and increase the mechanical properties of work-piece, the effects of welding parameters such as laser power, welding speed and defocusing value on both kinds of porosities were systemically analyzed respectively, and the shape and fluctuation of plume of the keyhole were observed to reflect the stability of the keyhole. The results show that increasing laser power or decreasing laser spot size can lead to the rising of both number and occupied area of pores in the weld; meanwhile, the plume fluctuates violently over the keyhole, which is always companied with the intense metallic vapor, liquid metal spatter and collapsing in the keyhole, thus more pores are generated in the weld. The porosity in the weld reaches the minimum at welding velocity of 2.0 m/min when laser power is 5 kW and defocusing value is 0.
基金the Natural Science Foundation of Jiangxi Province, China (No. 0650047)
文摘The semi-solid slurry of an A356 Al alloy, which was grain-fined by yttrium, was manufactured by low temperature pouring, The effects of grain-refining on the morphology and the grain size of the primary α phase in the semi-solid A356 Al alloy were researched. The results indicate that the semi-solid A356 AI alloy with particle-like and rosette-like primary α-Al can be prepared by low temperature pouring from a liquid grain-refined A356 alloy. The grain size and particle morphology of primary α-Al in the A356 Al alloy are markedly improved by the addition of 0.5 wt,% Y. The fining mechanism of Y on the morphology and grain size of the primary α-Al in the semi-solid A356 Al alloy was delved.
基金The project was financially supported by the Hi-tech Research and Development Program of China (No. G2002AA336080) and the National Natural Science Foundation of China (No. 50374012)
文摘The semi-solid slurry of a hypoeutectic Al-Si alloy was manufactured by low superheat pouring and weak electromagnetic stirring. The effects of pouting temperature and stirring power on the semi-solid slurry were investigated. The results indicated that the semi-solid slurry to satisfy rheocasting can be manufactured by low superheat pouring and weak electromagnetic stirring. The pouring temperature （or superheat） and the stirring power remarkably affected the morphology of primary α-Al and the size of primary α-Al, and there is no obvious effect of stirring time on primary α-Al. Compared with the samples made by low superheat pouring with no stirring, the nucleation rate, particle morphology and grain size of primary α-Al in A356 were markedly improved by low superheat pouring and weak electromagnetic stirring. On the condition of weak electromagnetic stirring, the pouring temperature with low superheat can be suitably raised to reach the effectiveness obtained from the lower pouring temperature without stirring.
基金This work was supported by The National Natural Science Foundation of China (Grant No. 59974009).
文摘A new method (liquidus casting) was used for 356 Al alloy semi-solid slurry making. The structures of 356 Al alloy cast by a Fe mould and semi-continuous casting machine at different temperatures were investigated. How the globular grains form was also discussed. The results show that either being cast by single Fe mould or semi-continuous machine, the micro structures are not conventional dendrites but fine and net-globular grains. The average gram size is smaller than 30μm and suitable enough for thixoforming, meanwhile it can improve the mechanical properties of following products. Under the suitable casting velocity and cooling intensity, most of global grains prolong their global growth and collide with each other before dendritic growth because of the large amount of the nucleation sites.
文摘Computer modeling of semi-solid structure formation is of significance in both understanding the mechanisms of globular structure formation and determining the effect of solidification conditions on final microstructure.A modified cellular automaton(mCA) model has been developed,which is coupled with macroscopic models for heat transfer calculation and microscopic models for nucleation and grain growth.The mCA model is applied to A356 Al alloy-one of the most widely used semi-solid alloys,to predict grain morphology and grain size during semi-solid solidification,and determines the effects of pouring temperature on the final microstructure.The modeling results show that the lower the initial temperature,the finer grain size will be obtained.In addition,the model can be used to predict the solutal micro-segregation.
