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Formation Mechanism of Ultrafine-Grained Structure by ECAP

ECAP超细晶结构的形成机制

基本信息

批准号：
10650693
负责人：
HORITA Zenji
金额：
$ 1.79万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

1. It was possible to obtain grain sizes of 〜μm for pure A1, 〜0.5μm for A1-1%Mg and 〜0.2 μm for A1-3%Mg using equal-channel angular pressing. Addition of Mg was effective to grain refinement of A1. The refinement was achieved because of the reduction in dislocation mobility and to the consequent lower rates of recovery in the solid solution alloys.2. The direct measurements of sample temperature during ECA pressing revealed that the temperature increase is 〜30° for pure A1 and 〜70° for an A1-3%Mg alloy. There was a linear correlation between the temperature increase and the applied load. However, such temperature increases did not affect the fine grain structure during ECA pressing.3. The microstructure did not change irrespective of the pressing speeds within the range of 0.18 mm/min to 18 mm/mini.4. The addition of 0.2%Sc to an A1-3%Mg alloy retained the ECA-pressed small grain size up to a temperature of 450℃. This alloy exhibited the superplastich elongation more than 1000% at a relatively lower temperature of 300℃ with a high strain rate of 3.3x10ィイD1-2ィエD1s-ィイD11ィエD1.5. ECA pressing at elevated temperatures showed that subgrain structures are developed at and above the temperature of 200℃ for pure A1 and A1-3%Mg. However, fine grain structures with high angle grain boundaries were obtained even at a temperature of 300℃. The presence of thermally stable particles was important for the retention of the fine grain structures.

1.采用等径角挤压工艺，纯Al的晶粒尺寸可达1.5 μm，Al-1%Mg的晶粒尺寸可达1.5 μm，Al-3%Mg的晶粒尺寸可达1.2 μm。Mg的加入对A1合金的晶粒细化效果明显。细化的实现是因为位错活动性的降低和固溶体合金中相应的较低的回复率。直接测量ECA挤压过程中试样的温度表明，纯Al的温度升高约30°，Al-3%Mg合金的温度升高约70°。温度升高与所施加的载荷之间存在线性相关性。然而，这样的温度升高并不影响ECA压制过程中的细晶结构.在0.18 mm/min至18 mm/min的范围内，无论压制速度如何，微观结构都没有变化。添加0.2%Sc的A1-3%Mg合金在450℃温度下仍能保持小晶粒。该合金在300℃的较低温度和3.3 × 10 ~（-1）Pa·D_（1 -2）Pa·D_（1 s-11）Pa·D_（1.5）的高应变速率下，超塑性延伸率超过1000%。高温ECA压制表明，纯Al和Al-3%Mg在200℃及以上的温度下形成亚晶组织。然而，即使在300℃的温度下也获得了具有大角度晶界的细晶组织。热稳定颗粒的存在对于保持细晶粒结构是重要的。