不同时效态7050铝合金时效成形中析出相对应力松弛行为的影响

铝合金时效成形方法结合了合金的蠕变松弛和析出强化作用,作为一种先进的整体壁板制造技术倍受航空制造业青睐。7xxx系铝合金在时效成形过程中的应力松弛行为受到合金内析出相与位错蠕变交互作用的影响从而制约着成形后零件质量与性能。本文采用设计的应力松弛试验研究了不同时效态(固溶态,欠时效态和峰时效态)7050铝合金内析出相对时效成形过程中应力松弛行为的影响,并通过位错热激活动力学参数计算和显微组织表征分析析出相与位错运动的交互作用。结果表明时效成形过程中析出相对位错热激活运动有明显地阻碍作用,因此含有不同尺度析出相铝合金的应力松弛行为表现不同,随着析出相尺度的增加合金应力松弛速率减缓,应力松弛极限增大。不同时效态7050铝合金位错激活体积计算和显微组织表征结果都证明了应力松弛过程中析出相增大对位错运动的阻碍作用也越显著。峰时效态7050铝合金的位错激活体积最大,时效成形后塑性应变的转化率最低。此外,时效成形过程中,7050铝合金内析出相对位错热激活的阻碍作用引起了槛应力现象,且随着析出相的增大槛应力也逐渐增大。

Effect of precipitates on stress relaxation behavior of 7050 Al alloy with different tempers during creep age-forming process

Creep age-forming combined creep and precipitation strengthening on aluminum alloy is an advanced integrated panel forming technology in the aerospace industry, and has been widely studied. The interaction between precipitation and dislocation creep in7xxx series aluminum alloy significantly affect on stress relaxation behavior, which decides the forming quality and properties of integrated panel, during age-forming process, since 7xxx series aluminum alloy as a typical age-hardening alloys. In this paper, the effect of different size precipitates on stress relaxation behavior of 7050 aluminum alloy during age-forming process has been investigated, which is helpful to apply creep age-forming technology of 7xxx series aluminum alloy with different tempers. The precipitates can obstruct dislocation thermal activation, therefore 7050 aluminum alloy with different size precipitates obviously exhibits different stress relaxation behavior, and relaxation rate decreases and relaxation limit increases with increasing precipitates size respectively. The calculation of dislocation activation volume and microstructure characterization proves that the obstruction to dislocation motion from precipitates improves with increasing precipitates size. Besides, a special threshold stress phenomena was present in the stress relaxation of the age-forming process, which was scribed to the interaction between precipitation and dislocation in 7050 aluminum alloy.