Published online by Cambridge University Press: 16 February 2011
It has been expected that “High rate superplastic materials” will be developed for industrial applications. The Dorntype equation for high temperature deformation suggests that strain rate can be increased if the grain size is decreased. This means that grain refinement can effectively establish high strain rate superplastic materials.
It is well known that a high degree of grain size refinement will result from the addition of zirconium to Al-base alloys. Powder-metallurgical processing with rapidly solidified powders is also available for the improvement of superplasticity by both the refinement of the solidified structure and the maintenance of the stable fine structure of a 7475 Al alloy during recrystallization and deformation. Therefore. P/M 7475 Al alloys containing Zr up to 0.9 wt% were selected as candidate specimens. The objective of the present paper includes the clarification of the role and the effective amount of Zr to obtain high strain rate superplastic materials. As a result, the addition of 0.3%Zr or more is effective in grain refinement of the P/M 7475 Al alloy. However, alloys containing 0.7 and 0.9 wt%Zr only show superplasticity at 793K. The optimum strain rate is shifted to a higher range with increasing Zr. The alloy of 7475 Al-0.9%Zr shows the maximum elongation of 900% at the remarkably high strain rate of 3.3×10−1 s−1.
The deformation mechanism of such high stain rate superplasticity will be discussed briefly, by considering the effect of the fine particles of Zr on superplastic behavior.
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