Weimin MAO
,
Zisheng ZHEN
,
Shijian YAN
,
Xueyou ZHONG
材料科学技术（英）
The rheological behavior and microstructure of semi-solid AZ91D was studied using a Couette type viscometer. The results show that the apparent viscosity of semi-solid AZ91D increases with the cooling rate increasing when it is continuously cooled and mechanically stirred and the empiric relation of the apparent viscosity with the cooling rate and solid fraction at shearing rate 93.7 s-1 is expressed as η=[0.66-0.63e(-ε3.01)]e (fs/0.14), and with the shearing rate and solid fraction at cooling rate 4ºC/min is shown as η=0.55e(fs/0.11- /87.59), as well as the cooling rate and shearing rate have an important effect on the microstructure of the semi-solid AZ91D alloy slurry, and decreasing the cooling rate and increasing the shearing rate are favorable to the nondendritic evolution of the primary grains.
关键词:
Rheological behavior
,
null
,
null
Weimin MAO
,
Heng JIANG
,
Ping YANG
,
Huiping FENG
,
Yongning YU
材料科学技术（英）
The distribution of microelement Fe, Si, Cu and Mg in the surface layer of aluminum foil annealed at 300℃ and 500℃ were determined by secondary ion mass spectrometer. The corrosion structure produced by electrochemical etching was also observed. It was found that the Mg concentration at external surface was increased exponentially over the fourth degree and promoted by higher annealing temperature, which will increase the number of corrosion pits inside the large grains, and therefore the specific capacity of the foils for electrolytic capacitors. The similar effects of microelement Fe, Si and Cu were not so strong.
关键词:
Electrolytic capacitor
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null
,
null
,
null
Weimin MAO
,
Yongning YU
,
Hong YANG and Bo SONG (Dept. of Materials Science and Engineering
,
University of Science and Technology Beijing
,
Beijing 100083
,
China)
材料科学技术（英）
The texture evaluation of α2 phase in Ti-25Al-10Nb-3V-1Mo sheet during rolling and annealing has been investigated by means of microstructure observation and ODF analysis. From the weak initial {1010} (1210) and {0001}(1210) textures a {1210}(1010) texture and a {0001}(uvtw)fibre texture are formed after cold rolling. The {0001} (1210) texture is also strengthened simultaneously. The activation process of slip systems is discussed concerning formation of the rolling texture. Because of the disappearance of {0001} (nvtw) fibre texture the primary recrystallization process should occur and the {1210}(1010) texture forms during annealing
关键词:
Weimin MAO
材料科学技术（英）
The effects of pouring temperature, short electromagnetic stirring with low strength and then soaking treatment on the microstructure of AlSi7Mg alloy were investigated. The results show that if AlSi7Mg alloy is poured at 630 or 650℃ and meanwhile stirred by an electromagnetic field at a low power for a short time, the pouring process can be easily controlled and most solidified primary α-Al grains become spherical and only a few of them are rosette-like. Weak electromagnetic stirring makes the temperature field more homogeneous and makes the primary α-Al grains disperse in a larger region, which leads to the spherical microstructures of primary α-Al grains. When the AlSi7Mg alloy is soaked or reheated at the semisolid state, the primary α-Al grains ripen further and they become more spherical, which is favorable to the semi-solid forming of AlSi7Mg alloy.
关键词:
AlSi7Mg alloy
,
alloy
,
semi-solid
,
pouring
,
tempera
Weimin MAO
材料科学技术（英）
The formation process of copper type rolling texture in f.c.c. metals was simulated based on a deformation model considering internal reaction stresses induced by the neighboring matrix as well as external shear stress induced by rollers. It is indicated that the external shear stress will reduce the brass type texture and increase the copper type texture obviously.
关键词:
Texture
,
null
,
null
,
null
Weimin MAO
,
Aimin ZHAO
,
Dong YUN
,
Leping ZHANG
,
Yonglin KANG
材料科学技术（英）
The nondendritic semi-solid slurry preparation of 60Si2Mn spring steel has been studied in this paper. The experiments have shown that when stirred for 2 min on the test condition, the semi-solid slurry with 50%~60% fraction solid and spherical primary austenitic grains in the size of 100~300 μm can be obtained and is easy to be discharged from the bottom little hole of the stirring chamber. The nondendritic slurry of 60Si2Mn spring steel can be rolled into given plate form successfully, but the solid phase and liquid phase is easy to be separated in rolling process so that the solid primary austenite is concentrated in the center and the liquid is near the edge of the rolled plate. The rupture strength and elongation of the plate rolled only once with semi-solid slurry are lower than that of the traditionally repeated hot-rolled plate of 60Si2Mn spring steel.
关键词:
60Si2Mn
,
null
,
null
,
null
Weimin MAO
,
Dong LI
材料科学技术（英）
The image stress of straight screw dislocations parallel to the medium surface covered by thin heterogeneous films was analyzed and deduced, in order to calculate the image shear stress. The relationship between image stress and distance from the screw dislocation to the interface of pure aluminum and its oxide covering was calculated based on the analysis. It was shown quantitatively that a sign conversion of the image stress appears in the case of thin oxide covering, while dislocation would pile up near the interface because of the possible slips of the screw dislocations induced by the image stress, which might break down the very thin oxide covering. Further investigation on edge dislocations or other dislocation configurations need to be done.
关键词:
Dislocation
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null
,
null
,
null
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null
,
null
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null
