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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. 采用等通道角挤压法，纯A1、A1-1% mg和A1-3% mg的晶粒尺寸分别为~ μm、~ 0.5μm和~ 0.2 μm。Mg的加入有利于A1的晶粒细化。这种细化是由于位错迁移率的降低以及由此产生的固溶体合金中较低的回收率。在ECA挤压过程中对试样温度的直接测量表明，纯A1的升温幅度为~ 30°，A1-3% mg合金的升温幅度为~ 70°。温度升高与外加载荷呈线性相关。然而，这种温度的升高并没有影响ECA挤压过程中的细晶粒结构。在0.18 mm/min ~ 18 mm/min的挤压速度范围内，微观组织没有发生变化。在A1-3%Mg合金中加入0.2%Sc后，直至450℃时仍能保持eca压制的小晶粒尺寸。该合金在相对较低的300℃温度下表现出超过1000%的超塑性伸长率，应变率为3.3 × 10的1 ~ 2的γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ。高温ECA压制表明，纯A1和A1-3% mg合金在200℃及以上均出现亚晶组织。然而，在300℃的高温下，仍可获得具有高角度晶界的细小晶粒组织。热稳定粒子的存在是保持细晶粒结构的重要因素。