Grain refinement in magnesium alloys by aging-rolling-aging method and by rolling in two phase region.

提出了一种制备细晶镁合金的新工艺。剧烈的变形和时效方法可以导致这种材料，但是，例如ECAP方法、高挤压比的挤压或多轴锻造不能应用于大尺度的材料。箔冶金可以应用于片状材料，但不适合连续生产。简单的轧制时效方法在大规模应用和连续生产中具有优势。这种方法的晶粒细化机理是基于动态再结晶的。因此，首先对高纯镁的再结晶进行了研究。在室温下对厚度约为10 × 10 mm^2和0.8 mm的纯镁试样进行冷轧，其不同的还原率可达80%。透射电镜（TEM）观察表明，冷轧后的再结晶率约为30%，而冷轧后的再结晶率约为80%。对试件位错的Burgers矢量分析表明，即使在室温下，非基底滑移系统仍在运行。镁具有易于再结晶的固有特性。然而，在纯镁的情况下，晶粒长大的再结晶晶粒发生。析出物似乎对晶粒生长有抑制作用。对镁锂锌合金进行固溶热处理、时效后在α+β两相区温度范围内进行热轧，使α和β晶粒均细化。然而，Mg-Li-Zn合金一般不用于工程材料。因此，对AZ31B和AZ91E镁合金采用相同的轧制时效工艺。AZ31B合金的晶粒尺寸由固溶热处理时的约50 ~ 100 μm减小到固溶热处理后的约3 ~ 5 μm。AZ91E合金为铸造合金，晶粒尺寸由200 μm左右减小到20 μm左右。对工程镁合金进行了成功的晶粒细化，但合金的织构表现为基面垂直于试样表面，这是镁合金板材的一般织构。为了既能获得细晶粒的显微组织，又能获得非基底织构，我们新开发了另一种方法，即将薄片试样热压成波浪状，并以45度旋转试样15 ~ 18次重复压制。该方法成功地达到了目的。少

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 … More 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