| Budget Amount *help |
¥14,700,000 (Direct Cost: ¥14,700,000)
Fiscal Year 2004: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2003: ¥10,100,000 (Direct Cost: ¥10,100,000)
Fiscal Year 2002: ¥3,900,000 (Direct Cost: ¥3,900,000)
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| Research Abstract |
A new technique for preparing magnesium alloys having fine grained microstructures has been developed. Severe deformation and aging method can lead to such materials, but, for example, ECAP method, extrusion with high extrusion ratios or multi axes forging could not be applied to materials with large scales. Foil metallurgy may be applied to sheet materials, but it is not appropriate for continuous production. Simple rolling and aging method seems to have advantages in large scale application and continuous production. Mechanism of the grain refining in this method is based on dynamic recrystallization.
Therefore, recrystallization in high purity magnesium was firstly investigated. Specimens of pure magnesium of about 10 x 10 mm^2 and 0.8 mm in thickness were cold rolled at room temperature with various reduction rates up to 80 %. Transmission electron microscopic(TEM) observations showed that recrystallization occurred in cold-rolled at about 30%, and in the specimen cold-rolled at abo
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ut 80%, recrystallization occurred in a large area of the specimen. Burgers vector analyses of dislocations in the specimen showed that non-basal slip system was operated even at room temperature. Magnesium has an intrinsic property for easily recrystallizing. However, in the case of pure magnesium, grain growth of recrystallized grains occurs.
Precipitates were seemed to be effective to suppress the grain growth. Magnesium-lithium-zinc alloys were solution heat treated, aged and then hot-rolled at the temperature range corresponding to two phase (α+β) region, which lead to grain refining in both the α and β grains. However, Mg-Li-Zn alloys are not generally used for engineering materials. Therefore, the same process composed of rolling and aging was applied to AZ31B and AZ91E magnesium alloys. On the AZ31B alloy, grain size was decreased from about 50 to 100 μm in solution heat treated condition to about 3 to 5 μm after the treatment. While on the AZ91E alloy, which was as cast alloy, grain size was decreased from about 200 μm into 20 μm in diameter.
Grain refining on engineering Mg alloys was successfully carried out as mentioned above, however, textures of the alloys showed that the basal plane was perpendicular to the specimen surface, the general texture of magnesium alloy sheets. In order to accomplish both the fine-grained microstructures and non-basal textures, we have newly developed another method, that is, the sheet specimen was hot-pressed to be formed a wavy shape, the pressing was repeated with rotating the specimen at 45 degrees for 15 to 18 times. The aim has been successfully achieved by the method. Less
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