The cast structure of a K465 nickel-based superalloy with different temperatures of melt superheating treatment was studied. It is shown that melt superheating treatment plays a significant role in the grain size and ...The cast structure of a K465 nickel-based superalloy with different temperatures of melt superheating treatment was studied. It is shown that melt superheating treatment plays a significant role in the grain size and carbide morphology. With increasing melt superheating temperature (below 2023 K),the grain size increases obviously and the carbide morphology is changed from a blocky to a script-like shape. However,when the melt superheating temperature is between 2023 K and 2123 K,the grain size decreases gr...展开更多
The isothermal compression test at elevated temperature was carried out for aluminum sheets prepared by different melt-treatment methods with aid of dynamic hot/mechanical simulation experimental technology. The mater...The isothermal compression test at elevated temperature was carried out for aluminum sheets prepared by different melt-treatment methods with aid of dynamic hot/mechanical simulation experimental technology. The material constants of hot deformation have been solved by multivariate regression directly. Influence of metallurgy factors on the constants was analyzed. The results show that at some strain, the relationship of sheets’ flow stress with deformation temperature and strain rate can be expressed more suitably with Arrhenius equation modified by hyperbolic sine function. Structure factor A1, stress-level coefficient α, strain rate sensibility exponent m and deformation activation energy Q all increase with increment of strain, while stress exponent n decreases gradually. The bigger α value or the smaller n value is, the more obvious the dynamic softening is, but the α value will increase for the metallurgy defects existing in the sheets. Influence of melt-treatment on Q depends upon the synthesis effect of all kinds of metallurgy defects. The Q and n values of the sheet prepared by high-efficient melt-treatment are the least, while the m value is the biggest, and the sheet can deform easily and evenly.展开更多
To increase the casting quality of hypoeutectic Al-Si alloys, the effects of melt thermal treatment on the solidification structure of the A356 alloy were analyzed by a factorial experiment, in which the overheated me...To increase the casting quality of hypoeutectic Al-Si alloys, the effects of melt thermal treatment on the solidification structure of the A356 alloy were analyzed by a factorial experiment, in which the overheated melt was mixed with the low temperature melt. Experimental results show that the elongation ratio and strength of the treated samples increase remarkably compared with the control sample. The primary dendrite size reduces dramatically and the dendrite changes from columnar to equiaxed, with a little change of the secondary dendrite arm spacing (SDAS). Combined with the measurement of the nucleation undercooling, it is concluded that the solidification structure and refining effect are dependent primarily on the low temperature melt. The refining mechanism is believed as a result of the multiplication of the nuclei in the melt thermal treatment procedure.展开更多
Influences of the three melt treatment processes (namely, refinement with carbon inoculation, electromagnetic stirring and "refinement & electromagnetic stirring" processing) on the microstructures of AZ...Influences of the three melt treatment processes (namely, refinement with carbon inoculation, electromagnetic stirring and "refinement & electromagnetic stirring" processing) on the microstructures of AZ91D alloy were explored experimentally. The results indicate that the micron carbon powders inoculation processing with 0.1% (mass fraction) addition level makes the grain size of the primary phase (α-Mg) decrease to approximate 40% that of the initial primary crystal, from about 530 μm to 200 μm around. The electromagnetic stirring processing not only decreases the grain sizes sharply, but also transfers the grain shape of α-Mg from coarse dendritic to nearly spheralitic with the shape factor from about 0.1 to approximate 0.8. And the "refinement & electromagnetic stirring" processing improves grain shape of α-Mg further and refines grain size to about 72 μm, less than 15% that of the initial primary crystal.展开更多
Effects of the melt pulse electric current and thermal treatment on solidification structures of A356 alloy were investigated. In the experiments, the low temperature melt(953 K and 903 K) treated by pulse electric cu...Effects of the melt pulse electric current and thermal treatment on solidification structures of A356 alloy were investigated. In the experiments, the low temperature melt(953 K and 903 K) treated by pulse electric current was mixed with high temperature melt(1 223 K). By the control experiments, the results show that the solidification structure of A356 alloy is refined apparently by the pulse electric current together with melt thermal treatment process, and the mechanical properties, especially the elongation ratio of the specimen treated is improved greatly. The structure change of the melt by pulse electric current and melt thermal treatment is the main reason for the refinement of the solidification structure of A356 alloy.展开更多
The melt treatment of A1-7%Si alloy by the flux injection method in a resistance furnance was investigated. The experimental results show that the flux injection method can realize the melt treatment of A1-7%Si alloy....The melt treatment of A1-7%Si alloy by the flux injection method in a resistance furnance was investigated. The experimental results show that the flux injection method can realize the melt treatment of A1-7%Si alloy. In purification, the flux injection method is superior to the standard lance degassing method. For the injection flux, the purifier Na2SiF6 is more powerful than Na3A1F6, the modifiers SrCl2, and R.E. Cl3 are quick acting, like NaF, but less powerful, the grain refiner containing K2TiF6 and KBF4 with Ti/B=1 is more potent than that with Ti/B=5. The analytical results indicate that the mass-transfer rate for the flux injection method is much higher than that for the conventional method .展开更多
文摘The cast structure of a K465 nickel-based superalloy with different temperatures of melt superheating treatment was studied. It is shown that melt superheating treatment plays a significant role in the grain size and carbide morphology. With increasing melt superheating temperature (below 2023 K),the grain size increases obviously and the carbide morphology is changed from a blocky to a script-like shape. However,when the melt superheating temperature is between 2023 K and 2123 K,the grain size decreases gr...
基金Project(JA04251) supported by the Education Department of Fujian Province, China Project(E0210011) supported by the Natural Science Foundation of Fujian Province, China
文摘The isothermal compression test at elevated temperature was carried out for aluminum sheets prepared by different melt-treatment methods with aid of dynamic hot/mechanical simulation experimental technology. The material constants of hot deformation have been solved by multivariate regression directly. Influence of metallurgy factors on the constants was analyzed. The results show that at some strain, the relationship of sheets’ flow stress with deformation temperature and strain rate can be expressed more suitably with Arrhenius equation modified by hyperbolic sine function. Structure factor A1, stress-level coefficient α, strain rate sensibility exponent m and deformation activation energy Q all increase with increment of strain, while stress exponent n decreases gradually. The bigger α value or the smaller n value is, the more obvious the dynamic softening is, but the α value will increase for the metallurgy defects existing in the sheets. Influence of melt-treatment on Q depends upon the synthesis effect of all kinds of metallurgy defects. The Q and n values of the sheet prepared by high-efficient melt-treatment are the least, while the m value is the biggest, and the sheet can deform easily and evenly.
基金The authors wish to thank General Motor (China) Inc. for the financial support of this work. Special thanks go to the Focus-group Principal Investigator Dr.Herbert W.Doty, and Dr.Bob Powell.
文摘To increase the casting quality of hypoeutectic Al-Si alloys, the effects of melt thermal treatment on the solidification structure of the A356 alloy were analyzed by a factorial experiment, in which the overheated melt was mixed with the low temperature melt. Experimental results show that the elongation ratio and strength of the treated samples increase remarkably compared with the control sample. The primary dendrite size reduces dramatically and the dendrite changes from columnar to equiaxed, with a little change of the secondary dendrite arm spacing (SDAS). Combined with the measurement of the nucleation undercooling, it is concluded that the solidification structure and refining effect are dependent primarily on the low temperature melt. The refining mechanism is believed as a result of the multiplication of the nuclei in the melt thermal treatment procedure.
文摘Influences of the three melt treatment processes (namely, refinement with carbon inoculation, electromagnetic stirring and "refinement & electromagnetic stirring" processing) on the microstructures of AZ91D alloy were explored experimentally. The results indicate that the micron carbon powders inoculation processing with 0.1% (mass fraction) addition level makes the grain size of the primary phase (α-Mg) decrease to approximate 40% that of the initial primary crystal, from about 530 μm to 200 μm around. The electromagnetic stirring processing not only decreases the grain sizes sharply, but also transfers the grain shape of α-Mg from coarse dendritic to nearly spheralitic with the shape factor from about 0.1 to approximate 0.8. And the "refinement & electromagnetic stirring" processing improves grain shape of α-Mg further and refines grain size to about 72 μm, less than 15% that of the initial primary crystal.
文摘Effects of the melt pulse electric current and thermal treatment on solidification structures of A356 alloy were investigated. In the experiments, the low temperature melt(953 K and 903 K) treated by pulse electric current was mixed with high temperature melt(1 223 K). By the control experiments, the results show that the solidification structure of A356 alloy is refined apparently by the pulse electric current together with melt thermal treatment process, and the mechanical properties, especially the elongation ratio of the specimen treated is improved greatly. The structure change of the melt by pulse electric current and melt thermal treatment is the main reason for the refinement of the solidification structure of A356 alloy.
文摘The melt treatment of A1-7%Si alloy by the flux injection method in a resistance furnance was investigated. The experimental results show that the flux injection method can realize the melt treatment of A1-7%Si alloy. In purification, the flux injection method is superior to the standard lance degassing method. For the injection flux, the purifier Na2SiF6 is more powerful than Na3A1F6, the modifiers SrCl2, and R.E. Cl3 are quick acting, like NaF, but less powerful, the grain refiner containing K2TiF6 and KBF4 with Ti/B=1 is more potent than that with Ti/B=5. The analytical results indicate that the mass-transfer rate for the flux injection method is much higher than that for the conventional method .
