等径角挤压2A12铝合金超细晶组织结构研究

使用Φ=90°和ψ=30°的挤压模具在室温下对2A12铝合金进行了8次等径角挤压,成功制备了晶粒尺寸为200nm左右、具有大角度晶界的块体超细晶材料,并且采用HitachiS-800透射电镜,研究了挤压过程中2A12铝合金的组织结构及其变化。结果表明挤压一次后,晶粒内位错密度急剧增加,形成位错纠缠,晶粒细化效果最明显;挤压前分布在α-Al基体上的针状第二相Al2Cu和颗粒状Al2Cu Mg,在剪切力的作用下,针状Al2Cu变成颗粒状,弥散分布在α-Al基体上,Al2CuMg颗粒因晶粒细化进入了晶界位置,而且在以后的挤压中,这些化合物颗粒大小基本保持不变。继续挤压,位错逐渐由晶内移动到晶界上,在晶界上形成胞状组织,最后逐渐变成了清晰的小角度晶界或大角度晶界,从而实现组织的超细化。

Microstructure of Ultrafine-grained 2A12 Aluminum Alloy Pressed by Equal-channel Angular Pressing

The bulky ultra-fine 2A12 aluminum alloy with grain size about 200 nm and high angular boundary can be prepared by 8-turns pressing with ECAP die with the inner angle 90 and outer angle 30 at ambient temperature, and the microstructure and its evolution of the 2A12 aluminum alloy during pressing were observed by Hitachi S-800 TEM. The results show that grain size is significantly refined due to the sharply increases of dislocation density in grain resulting in dislocation tangle after one-turn pressing. Needle-like secondary phase Al2Cu is transformed into particle , dispersing in a-Al matrix, and Al2 CuMg particle is pressed into grain boundary due to the refinement of the grain size with shearing, where these compound particles are not changed in the following pressing process. The 2A12 aluminum alloy with ultra-fine structure can be prepared due to the dislocation gradually moving from grain towards grain boundary, and forming cell structure on grain boundary, finally gradually becoming clear small angular boundary or large angular boundary by continuously pressing.