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

开发了一种制备细晶组织镁合金的新技术。严重的变形和时效方法可以导致这类材料的产生，但ECAP法、高挤压比挤压或多轴锻造等方法不能用于大型材料。箔冶金可以应用于薄板材料，但不适合连续生产。简单的轧制和时效方法在大规模应用和连续生产方面似乎具有优势。该方法的晶粒细化机理是基于动态再结晶的，因此，本文首先对高纯镁的再结晶进行了研究。对厚度分别为10×10 mm^2和0.8 mm的纯镁样品进行了室温冷轧，不同的压下率可达80%。透射电子显微镜观察表明，在30%左右的冷轧条件下，再结晶发生，在ABO…冷轧条件下，再结晶发生。超过80%时，再结晶出现在大范围的试件中。对样品中位错的Burgers矢量分析表明，即使在室温下，非基面滑移系统也是起作用的。镁具有易于再结晶的固有特性。然而，在纯镁的情况下，出现了再结晶晶粒的长大，沉淀物似乎有效地抑制了晶粒的长大。对镁锂锌合金进行固溶处理、时效，然后在对应于两相(α+β)区的温度范围内进行热轧，使α和β的晶粒都得到细化。然而，镁锂锌合金并不是常用的工程材料。因此，对AZ31B和AZ91E镁合金采用相同的轧制和时效工艺。AZ31B合金固溶热处理后，晶粒度从50~100μm左右减小到3~5μm左右。而铸造镁合金AZ91E的晶粒度从200μm左右减小到20μm左右，成功地对工程镁合金进行了细化处理，但织构表明，合金的基面垂直于试件表面，具有镁合金板材的一般织构特征。为了同时获得细晶组织和非基织构，我们又开发了另一种方法，即将片状试件热压成波浪形，以45度旋转试件15~18次重复压制。该方法已成功地实现了这一目的。较少

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