FABRICATION OF HIGH STRAIN RATE SUPERPLASTIC ALLOYS USING INTENSE PLASTIC STRAINING

等通道角（ECA）挤压能够在块状材料中引入超细晶粒尺寸，微观结构的精确性质取决于挤压、温度和速度所引入的总应变。当应变足够高时，有可能在高应变率下获得非常高的拉伸延展性。值得注意的是，使用不同的加工路线提供了改变样品内剪切面和剪切方向的机会，从而以有利的方式修改由ECA压制引起的微观结构。已知三维剪切组合有效地增加了每次挤压过程中形成的错取向量。即使在高纯度铝中，获得的晶粒尺寸也小至1.2微米。当加入合金元素时，获得的晶粒尺寸明显减小。高h是实现高应变速率超塑性的先决条件，为了提高细晶粒尺寸的高温稳定性，需要细颗粒的分散。目前的结果非常清楚地证明了晶粒尺寸的细化和由此产生的有利的高应变速率超塑性，这可以通过ECA压制和显微组织控制在典型的商用Al-Mg-Li-Zr合金中实现，其中沉淀存在，即使在快速扩散的高温下也能保持超细晶粒尺寸。化学成分为Al-6% Cu-0.4% Zr的商用Al-2004合金Supral 100也实现了类似的晶粒细化和高应变率超塑性。此外，在室温下，在不使用任何中间加热的情况下，通过ECA压制获得了Al-3%Mg-0.2%Sc合金的异常高应变速率超塑性。在Al-Mg-Sc合金中，细小弥散的Al_3 -Sc相抑制晶界的迁移，进而增强晶界滑动，Mg抑制晶粒中的位错滑动，强化基体固溶。目前的工作也提供了潜力，大大提高可行性的超塑性成形在金属成形工业。少

The equal-channel angular (ECA) pressing is capable of introducing an ultrafine grain size into bulk materials and the precise nature of the microstructure is dependent upon the total strain introduced by the pressing, temperature and speed of pressing. When the strain is sufficiently high, it is possible to achieve very high tensile ductilities at high strain rates. It is noted that the use of different processing routes provides an opportunity to alter the shearing planes and shear directions within the sample and therefore to modify, in a favorable manner, the microstructures induced by ECA pressing. It is known that the combination of shear in three dimensional way is effective to increase the amount of misorientation formed during each pressing. The attained grain size is as small as 1.2 micrometers even in high purity aluminum. When the alloying elements are added, the attained grain size reduced appreciably. To increase the elevated temperature stability of fine grain size, whic … More h is a prerequisite for attaining high strain rate superplasticity, a fine dispersion of particles is required. The present results provide a very clear demonstration of refinement of grain size and resultant advantageous high strain rate superplasticity which may be achieved by ECA pressing and microstructural control in a typical commercial Al-Mg-Li-Zr alloy where precipitates are present to retain the ultrafine grain sizes even at high temperatures where diffusion is rapid. Similar grain refinement and high strain rate superplasticity are achieved also in a commercial Al-2004 alloy known as Supral 100 with a chemical composition of Al-6% Cu-0.4% Zr. Furthermore, the exceptionally high strain rate superplasticity of the Al-3%Mg-0.2%Sc alloy was achieved by ECA pressing at room temperature without the use of any intermediate heating. In the Al-Mg-Sc alloy, the migration of grain boundaries are suppressed by the fine dispersion Al_3 Sc phase and then enhancing the grain boundary sliding and the matrix is solution strengthened by Mg suppressing the dislocation glide in the grains. The present work also provides the potential for substantially increasing the viability of superplastic forming in the metal forming industry. Less