挤压态7A85铝合金高温热变形显微组织演变

Microstructure Evolution of As-extruded 7A85 Aluminum Alloy during High Temperature Deformation

7A85铝合金密度小、强度高、热加工性能好、焊接性能优良,而且具有较好的耐腐蚀性和较高的韧性,广泛应用于航空和航天中的受力结构件.本文通过挤压态7A85铝合金的单向等温热压缩实验,利用光学显微镜、透射电镜研究了合金在变形温度为300℃,350℃,400℃,450℃,应变速率为0.01s^(-1),0.1s^(-1),1s-1,10s^(-1)时的高温流变行为和显微组织演变.结果表明:变形温度和应变速率对挤压态7A85铝合金热压缩后的组织有重要影响.随着变形温度的升高和应变速率的降低(lnZ减小),组织中亚晶长大,位错密度逐渐降低,析出相数量减少,再结晶晶粒长大,动态软化机制由动态回复转变为动态再结晶;挤压态7A85铝合金热压缩后组织中大量的析出相弥散分布在基体内或沿晶界分布,抑制了动态再结晶的发生.

7A85 aluminum alloy, possessing the characteristics of low density, high strength, excellent hot working property, fine weldability, good corrosion resistance and high toughness, has been widely used in aerospace and mechanical structural parts. High temperature rheological behavior and microstrueture e- volution of as-extruded 7A85 aluminum alloy were investigated by optical microscope（OM）, transmission electron microscope（TEM）and the unidirectional isothermal compression tests conducted at different tem- peratures（300,350,400 and 450~C）with different strain rates of 0.01,0.1,1 and 10 s-l.It is concluded that the deformation temperature and strain rate have an important effect on the microstructure of the as-extru- ded 7A85 aluminum alloy after hot compression.With the increase of deformation temperature and the de- crease of strain rate（decreasing of lnZ）,the subgrains and the reerystallization grains grow,the dislocation density and the quantity of precipitates decrease, and the softening mechanism transforms from dynamic re- covery to dynamic recrystallization. Plenty of precipitates of as-extruded 7A85 aluminum alloy after hotcompression,dispersing in the matrix or along the grain boundaries, inhibit the occurrence of dynamic re- crystallization.