Pengfa FENG
材料科学技术（英）
The influences of preparation conditions of Al-5Ti-B (as-cast and hot-rolled) and Al-10Sr (as-cast and hot-extruded) and melt treatment procedures on the grain refinement and modification performance of A356 alloy are experimentally studied. For the two master alloys, the 50% reduction is sufficient to meet the demands of the efficient grain refinement and modification of A356 alloy. When Al-5Ti-B is introduced into the melt prior to degassing, the grain refinement efficiency of Al-5Ti-B will be greatly increased due to the better dispersity of TiB2 particles. Al-5Ti-B master alloy is less prone to affect the modification effect of Al-10Sr when they are used together.
关键词:
Grain refinement
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中间合金
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热变形
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晶粒细化
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A356合金
Prapas Kunnam
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Chaowalit Limmaneevichitr
材料科学技术（英）
This paper presents the effects of different process parameters in producing Al-5Ti-1B grain refiner, i.e. various sequences and reaction time, on grain refinement efficiency of aluminum castings. It was found that different process parameters resulted in different morphology and size distribution of TiAl3 and TiB2 in grain refiner. The experiment was carried out by adding KBF4 and K2TiF6 to molten aluminum. The melting temperature was controlled at 800℃ in an electric resistance furnace. Three different sequences of KBF4 and K2TiF6 additions were applied, i.e., adding KBF4 before K2TiF6, adding K2TiF4 before KBF4 and mixing both KBF4 and K2TiF6 before adding to molten aluminum. Three different holding time at 1 min, 30 min and 60 min were applied. The results showed that no significant difference of morphology and size distribution was found by varying three different sequences. Whereas, the different holding time provided major differences in both morphology and size distribution, which are technically expectable from diffusion and agglomeration between particles resulting in larger particle size and wider range of size distribution of TiAl3 and TiB2. If the reaction time was longer than 30 min, morphology of both TiAl3 and TiB2 became too large. If the reaction time was too short, less reaction between TiAl3 and TiB2 to form would be obtained. For grain refinement efficiency, it was found that mixing KBF4 and K2TiF6 before adding to molten aluminum with a holding time of 30 min resulted in best grain refinement efficiency.
关键词:
Grain refinement
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null
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null
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null
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null
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null
Yichuan PAN
材料科学技术（英）
In this study, grain refining effect of Al-1.5C master alloy was examined on an AZ63B magnesium alloy, and the refining mechanism was studied through investigating the role of C and Fe in this process. The results show that addition of Al-1.5C master alloy leads to significant decrease of the mean grain size from about 270 μm to 50 μm at the center of the AZ63 alloy ingot. Grain refinement by carbon addition is mainly due to the heterogeneity nucleation on the Al-, C-, O-, Fe- and Mn-rich particles, but not constitutional undercooling caused by the carbon solute element. Fe plays an important role in the formation of the nucleating particles, but not acts as an inhibiting element.
关键词:
Grain refinement
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null
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null
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null
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null
Jianbo YU
,
Zhongming REN
金属学报(英文版)
doi:10.1016/S1006-7191(08)60068-X
The effects of electromagnetic vibration on the grain refinement in directional solidification were investigated. It was found that the electromagnetic vibration applied in the melt not only can refine grains remarkably but also can enhance both tensile strength and ductility values of Al-6%Si alloy. SEM graphs show that coarse dendrite structure was broken up into a somewhat globular structure, and the morphology of eutectic silicon was changed from flaky to fibrous under electromagnetic vibration treatment. The refine mechanism under electromagnetic vibration was discussed.
关键词:
Electromagnetic vibration
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null
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null
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null
Chunfang WANG
,
Maoqiu WANG
,
Jie SHI
,
Weijun HUI
,
Han DONG
材料科学技术（英）
Martensitic microstructure in quenched and tempered 17CrNiMo6 steel with the prior austenite grain size ranging from 6 μm to 199 μm has been characterized by optical metallography (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The yield strength and the toughness of the steel with various prior austenite grain sizes were tested and correlated with microstructure characteristics. Results show that both the prior austenite grain size and the martensitic packet size in the 17CrNiMo6 steel follow a Hall-Petch relation with the yield strength. When the prior austenite grain size was refined from 199 μm to 6 μm , the yield strength increased by 235 MPa, while the Charpy U-notch impact energy at 77 K improved more than 8 times, indicating that microstructure refinement is more effective in improving the resistance to cleavage fracture than in increasing the strength. The fracture surfaces implied that the unit crack path for cleavage fracture is identified as being the packet.
关键词:
Martensitic steel
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null
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null
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null
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null
M.-X.Zhang
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P.M.Kelly
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M.Qian
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J.A.Taylor
材料科学技术（英）
An edge-to-edge matching model has been used to analyze the crystallographic features between Mg matrix and three commonly accepted heterogeneous nucleants for Mg grains, Al4C3, Al2CO and Al8(Mn, Fe)5. The model has predicted that Al2CO is the most effective nucleant of the three compounds assessed for Mg grains and that Al4C3 can be a nucleant for Mg grains, but it is not as effective as Al2CO. This prediction is consistent with most recent experimental results. The Al8(Mn, Fe)5 intermetallic compound is predicted to have the lowest efficiency as a grain refiner. The model may be used to provide theoretical guidance for selection of new and potent grain refiners for Mg-Al based alloys.
关键词:
Crystallography
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null
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null
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null
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null
B.Eghbali
,
A.Abdollah-zadeh
材料科学技术（英）
Grain refinement is one of the effective methods to develop new generation low carbon microalloyed steels possessing excellent combination of mechanical properties. The microstructural evolution and ferrite grain refinement at the deformation temperature of 865℃, above Ar3, with different strain rates were investigated using single pass isothermal hot compression experiments for a low carbon Nb-Ti microalloyed steel. The physical processes that occurred during deformation were discussed by observing the optical microstructure and analyzing the true stress-true strain responses. At strain rates of 0.001 and 0.01 s-1, there is no evidence of work hardening behavior during hot deformation and strain-induced transformation (SIT) leads to dynamic flow softening in flow curves. Optical microscopy observation shows that ultrafine and equiaxed ferrite with grain sizes of 2μm can be obtained by applying deformation with strain rate of 0.1 s-1 due to SIT just after deformation. Furthermore, increasing the strain rate from 0.001 to 0.1 s-1 reduces both the grain size of the equiaxed ferrite and the amount of deformed ferrite.
关键词:
Low carbon microalloyed steel
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null
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null
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