Research on the Alloying Design for High Strain Rate Superplastic Materials

“高速率超塑性材料”有望在工业上得到应用。高温变形的dorn型方程表明，减小晶粒尺寸可以提高应变速率。这意味着晶粒细化可以有效地建立高应变速率超塑性材料。众所周知，在铝基合金中加入锆可以使晶粒细化到较高的程度。在7475铝合金再结晶和变形过程中，快速凝固粉末的粉末冶金处理也可通过细化凝固组织和保持稳定的精细组织来改善超塑性。因此，选择Zr含量高达0.9 wt%的P/M 7475铝合金作为候选试样。本项目的目的包括澄清Zr在获得高应变速率超塑性材料中的作用和有效量。结果表明，添加0.3%Zr及以上的zr对P/ m7475铝合金的晶粒细化效果较好。然而，含有0.7和0.9 wt%Zr的合金仅在793K时表现出超塑性。最佳应变速率随Zr的增大而增大。在3.3x10^<-1> s^<-1>的应变速率下，7475 Al-0.9%Zr合金的最大伸长率达到900%。通过考虑Zr的细颗粒对超塑性行为的影响，简要讨论了这种高染色率超塑性的变形机理。

It has been expected that "High rate superplastic materials" will be developed for industrial applications. The Dorn-type 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 project 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 3.3x10^<-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.