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通过形变热处理能使7475合金的晶粒尺寸细化到6和8μm.在440～545℃、2.8×10~(-4)～2.8×10~(-2)S~(-1)应变速率下,测定了这种材料的超塑性.合金的最大伸长率约为2000％,在2.8×10~(-3)S~(-2)应变速率下达到最大超塑性,其塑性高出一般7475合金一个数量级.这一结果是由于在相同高温下保持细晶粒的细小弥散体的存在所致.屈服应力和应变速率敏感指数主要依赖于晶粒尺寸。超塑性7475合金的应变速率敏感指数为0.67(晶粒为6μm)和0.5(晶粒为13μm),而激活能与铝晶界的扩散活相当.经超塑性试验的试样,显微组织检查表明晶界处的无弥散体带(dispersoid free zones)基本上垂直于拉伸方向.在伸长率为100％时.这些无弥散体带(DFZ)就会出现,其宽度偶尔大到5μm.这个结果表明在细晶粒的7475合金超塑性变形过程中,特别是在低延伸率的变形中扩散流动的重要性.
The grain size of the alloy 7475 can be refined to 6 and 8μm by the heat treatment at the temperature of 440 ~ 545 ℃ and the strain rate of 2.8 × 10 ~ (-4) ~ 2.8 × 10 ~ (-2) S ~ (-1) , The superplasticity of this material was measured.The maximum elongation of the alloy was about 2000%, and reached the maximum superplasticity at a strain rate of 2.8 × 10 -3 S -2, which was higher than the general plasticity of 7475 The alloy is an order of magnitude.This result is due to the presence of a fine dispersion that maintains fine grains at the same elevated temperatures.The yield stress and strain rate sensitivity index are mainly dependent on the grain size. The strain rate sensitivity index of superplastic 7475 alloy is 0.67 (grain size is 6μm) and 0.5 (grain size is 13μm), and the activation energy is comparable with that of aluminum grain boundary. The samples of superplasticity test, microstructure inspection The dispersoid free zones at the grain boundaries are shown to be substantially perpendicular to the direction of stretch, and at zero elongation these DFZ bands appear, occasionally as large as 5 μm in width. This result shows the importance of diffusive flow during the ultra-plastic deformation of the fine grained 7475 alloy, especially in the deformation of low elongation.