等通道挤压变形结合中间退火制备Al-7Mg合金的组织、硬度演变及热稳定性

在室温条件下采用Bc模式等通道挤压变形（ECAP）结合中间退火方法制备二元Al—7Mg合金。经6道次ECAP变形后，该材料硬度高达HV218。透射电镜（TEM）表征揭示该Al—7Mg合金的晶粒得到明显细化。经5或6道次变形后得到的超细晶组织平均尺寸为100～200nm。X射线衍射分析表明Mg主要以固溶原子的形式存在。因此，由于Mg偏析或析出相造成的可能强化影响均忽略不计。经6道次ECAP变形后的A1-7Mg合金的高硬度主要来自于晶界强化，大约占总强度的41％，其次，位错强化及Mg原子的固溶强化分别约占总强度的24％和35％。此外，通过测量硬度变化研究了该A1—7Mg合金的热稳定性。结果表明在250℃退火处理时该材料相对稳定，然而当温度升至300℃时，该Al—7Mg合金的软化趋势明显加快。

Microstructure,hardness evolution and thermal stability of binary A1-7Mg alloy processed by ECAP with intermediate annealing

A binary Al-7Mg alloy was processed by equal channel angular pressing （ECAP） at room temperature via route Bc, combined with intermediate annealing. After 6 passes, a high hardness of HV218 is achieved. Transmission electron microscopy （TEM） observations demonstrate that ECAP leads to a significant grain refinement and ultrafine grains down to 100-200 nm are developed after 5 or 6 passes. X-ray diffraction （XRD） analysis indicates that the major part of Mg atoms are in solid solution in the deformed material, and the possible strengthening effect of Mg solute atom clusters or precipitates is neglected. The high hardness of the 6 pass-treated materials comes mainly from grain boundary strengthening, which contributes about 41% to the total strength, while dislocations and Mg solid solution contribute about 24% and 35% to the remaining strength, respectively. Also, the thermal stability of this severely deformed material was investigated by hardness measurements. The material is relatively stable when annealed at a temperature lower than 250 ℃, while annealing at 300 ℃ leads to a rapid softening of the material.