超塑性 Al-5.5Mg-2.4Si 合金の変形特性

概要

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Deformation characteristics of a superplastic Al-5.5Mg-2.4Si prepared by a simple processing consisting of continuous casting, homogenizatin and cold rolling were examined. Strain rate sensitivity showed a maximum of 0.52 at 863K at a strain rate of 1×10^<-2>s^<-1>. The strain rate was 1 or 2 order higher than that of superplastic I/M 7475 or 5083 aluminum alloys. It is clear that the higher strain rate was obtained by a fine grain structure including a lot of sub-grains. The fine microstructure is due to retardation of recrystallization and grain growth at higher temperatures than 823K by secondary phase particles composed of Al, Si and Mn, which sometimes include Cr too. A maximum elongation of 900% was obtained at a lower strain rate of 1×10^<-4>s^<-1> at 863K while elongation was only 270% at the higher strain rate of 1×10^<-2>s^<-1>. This decrease of elongation may be due to the increase in volume fraction of cavities which increases with increasing strain rate. Cavities are sometimes observed near the secondary phase particles of Mg_2Si.
1992-11-15