Development of Ultrafine-Grained Metallic Materials Using Intense Plastic Straining Technique

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Grain size refinement of metallic materials has been attempted using an intense plastic straining technique. This study has covered examinations of microstructural evolution during refining process and of microstructural stability during static annealing. The results are summarized as follows.1. The strain introduced in the material was controlled by changing the angle where a channel was bent in a die. It was found that the grains with large misorientations between neighboring grains increased when a large strain was imposed by one pressing rather than by many pressings.2. Addition of Mg to Al was effective to grain size refinement : -1 mum for Al but -0.5 mum for Al-1%Mg and -0.2 mum for Al-3%Mg.3. There was almost no effect on the grain size when 0.12%Zr was added to Al, but the fine grain structure with a grain size of -1 mum remained stable up to a temperature of 300ﾟC which is higher by 100ﾟ than for Al. It was found that the presence of a fine dispersion of Al_3Zr particles was important for the inhibitation of significant grain growth.4. A grain size of -0.3 mum was attained in Cu.5. High-resolution electron microscopy revealed that the grain boundary structure exhibits more irregular configuration in Cu than in Al. It was concluded that the effect of recovery is less in Cu as the melting point of Cu is fairly higher than that of Al.6. It was concluded that the intense plastic straining technique is a useful method for the production of ultrafine grained materials. The grain size refinement is more effective for alloyed materials or for metals with higher melting temperatures.