Na Wang Zhimin Zhou
材料科学技术(英文)
The semi-solid billet of 6061 aluminum alloy was prepared by the near-liquidus semi-continuous casting (LSC) with rosette or near-spheroide grains. The pre-deformation processing was applied before partial remelting to further improve the microstructure and properties of the semi-solid alloy. The effects of different processing parameters, such as holding temperature and holding time, on the semisolid microstructures during partial remelting have been investigated. It was found that the optimal partial remelting parameters should be 630°C and 10{15 min for 6061 alloy cold rolled with 60% reduction in height of pre-deformation. The coarsening rates were anasysed by Lifshitz-Slyozov-Wagner (LSW) theory. The pre-deformed 6061 alloy exhibits lower coarsening rate constants than that of the as-cast one, and also lower than other alloys processed by different method found in previous literature. It is because the coarsening rate is associated with the initial microstructure and composition of the alloy. The secondary phases in the alloy inhibit the migration of the liquid film grain boundaries. The microstructure obtained by using the combination of near-liquidus semicontinuous casting and pre-deformation treatment is better than that without pre-deformation processing, which demonstrates that the used method is promising for fabricating high quality semi-solid alloys.
关键词:
Semi-solid forming
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Near-liquidus semi-continuous casting
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6061 alloy
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Pre-deformation
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Partial remelting
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Coarsening
A.A.Al-Aql
,
M.S.Al-Salhi
,
M.I.Ansari
材料科学技术(英文)
Precipitation study was carried out in Ni-35 at. pct Cr alloy by measuring electrical resistivity at different ageing temperatures and long ageing times. During ageing, it was observed that electrical resistivity initially rose with ageing time and then fell after very long ageing at a constant temperature. The initial increase in resistivity during ageing may be attributed to the formation of GP zones/Cr-rich precipitates at early stages by nucleation process and decrease in resistivity, and after attaining a maximum, is due to the growth of precipitate particles and subsequently by coarsening of these precipitates. The results of electrical resistivity measurements during ageing were confirmed by X-ray diffraction analysis indicating the formation of a Cr-rich phase and a Cr3Ni2 phase in the Ni matrix.
关键词:
Precipitation
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null
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null
,
null
,
null
Ming ZHANG
金属学报(英文版)
In order to reveal evolution of the rust layer during atmospheric corrosion, commercial weathering steel (WS) 09CuPCrNi and a recently developed bainite WS were subjected to a salt fog test. The protection and compactness of the rust layer were evaluated by electrochemical analysis, absorption-desorption test, etc. The experimental results indicate that more compact rust layer could be derived from the rust particles with larger size. The well-established notion that the rust particle growth can induce the decrement of corrosion resistance of WS. However, the present investigation shows that the notion might not be universally accurate. The unusual result means that the rust particles might grow anisotropically during corrosion.
关键词:
Weathering steel
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corrosion
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rust particle
,
coarsening