结合自然时效和大预变形提升Al-Mg-Si-Cu合金蠕变时效响应研究

Improvement of creep ageing response for Al-Mg-Si-Cu alloy combining natural-ageing and large pre-deformation

通过改变常规冷变形和自然时效顺序,提出一种结合自然时效和大预变形提高Al-Mg-Si-Cu合金蠕变量和力学性能的工艺。通过硬度测试、蠕变时效测试、拉伸力学性能测试和透射电镜观察,对比了常规处理和改进工艺处理的试样在蠕变时效过程中的硬度、蠕变量、力学性能和微观结构的演变规律。结果表明,改进工艺处理能够有效延长合金蠕变时效第1阶段的持续时间,24 h内的总蠕变量比常规处理的试样提高约1.5~3.2倍,也能够显著提高Al-Mg-Si-Cu合金的强度,同时保持合金的断后伸长率不降低。透射电镜观察结果显示,大预变形合金初始位错密度大并在蠕变时效过程中显著降低,在晶格缺陷的诱导下,Al-Mg-Si-Cu合金中形成了壁状析出相,该析出相在经常规蠕变时效的合金中并未被发现。建立了基于位错密度和应力阈值的本构方程,可以准确预测大预变形态Al-Mg-Si-Cu合金的蠕变时效行为。

A process method combining natural ageing and large pre-deformation to improve the creep strain and mechanical properties of Al-Mg-Si-Cu alloy was proposed by modifying the sequence of conventional cold-rolling and natural ageing. The evolution of hardness,creep strain,mechanical properties and microstructure of samples treated by conventional treatment and improved process were compared by hardness test,creep ageing test,tensile test and transmission electron microscopy( TEM) observation. The results show that the duration of the first creep stage can be effectively prolonged by the improved process,and the total creep strain within 24 h is approximately1. 5 ~ 3. 2 times higher than that of conventionally treated samples. Moreover,the strength of Al-Mg-Si-Cu alloy can be enhanced significantly while the elongation after fracture is not reduced. TEM observation results show that the initial dislocation density of the large pre-deformation alloy is high and significantly decreases during creep ageing. Induced by lattice defects,wall-like precipitates are formed in the AlMg-Si-Cu alloy,which are not found in conventionally creep-aged alloy. The constitutive equation based on dislocation density and stress threshold was established,which can predict the creep ageing behavior of Al-Mg-Si-Cu alloy with large pre-deformation accurately.