Integrating reversion ageing and forming of high-strength Al alloys: Principles and theoretical basis
Integrating reversion ageing and forming of high-strength Al alloys: Principles and theoretical basis
复制标题
DOI：
10.1016/j.ijmachtools.2023.104091
复制
发表时间：
2023-11
影响因子：
14
通讯作者：
Chunhui Liu;Jun He;Zhuangzhuang Feng;P. Ma;Lihua Zhan
中科院分区：
文献类型：
--
作者：
Chunhui Liu;Jun He;Zhuangzhuang Feng;P. Ma;Lihua Zhan
同时提高高强度铝（Al）合金（例如Al-Zn-Mg-Cu合金）的可成形性和成形后强度在制造复杂形状的面板部件中是必不可少的。热处理条件要求高、模具成本高限制了现有成形方法的应用。提出了一种新的工艺，称为集成回复时效和成形（IRAF）形成自然时效（NA或T4回火）铝合金。对IRAF工艺进行了基于原理的概念分析和系统的热力冶金研究。此外，进行拉伸试验以评估包括加热速率、保持时间和成形温度在内的参数对成形性和烘烤强度的影响。AA 7075-T4合金的可变形性可通过快速加热至回复时效温度（150-300 °C），随后短期保持而显著增强，如200 MPa的降低的屈服强度和增加的均匀延展性所证明的。在短烘烤硬化（BH）处理后，获得了瞬时强度增加到接近T6状态的值。此外，温度-时间-性能（TTP）图建立的基础上测得的机械性能和整个过程的微观结构演变之间的相关性，以解释IRAF的优化处理窗口的机制。结果表明，快速加热速率（>300 °C/min）促进了NA团簇的逆转，抑制了溶质的再沉淀，从而改善了热成形性。高于240 °C的回复时效可诱导粗的γ ′/η相的形成，导致BH响应显著下降。为了准确预测IRAF过程中的强度演化和变形行为，考虑NA团簇的逆转和溶质再析出，建立了基于物理的统一本构模型。对AA 7075-T4合金板的弯曲和拉伸试验验证了处于最回复状态的IRAF能够实现最佳成形性。这些发现启发了促进预先存在的亚稳颗粒的回复，以改善热成形性和成形后的时效硬化。
Simultaneously improving the formability and post-formed strength of high-strength aluminum (Al) alloys, such as Al–Zn–Mg–Cu alloys, is essential in manufacturing complex-shaped panel components. The strict requirements on heat-treatment condition and high tooling costs limit the applications of current forming methods. A novel process called integrated reversion ageing and forming (IRAF) is proposed to form naturally aged (NA or T4 tempered) Al alloys. A principle-based concept analysis and systematic thermo-mechanical-metallurgical study of the IRAF process were performed. Additionally, tensile tests were conducted to evaluate the effects of parameters including heating rate, holding time, and forming temperature on formability and baked strength. The deformability of the AA7075-T4 alloy can be significantly enhanced through rapid heating to the reversion ageing temperature (150–300 °C), followed by short-term holding, as evidenced by the reduced yield strength of 200 MPa and increased uniform ductility. An instant strength increase to a value close to that of the T6 state was obtained after a short bake hardening (BH) treatment. Further, temperature-time-property (TTP) diagrams were established based on the correlation between the measured mechanical properties and through-process microstructure evolution to explain the mechanism underlying the optimised processing window of IRAF. The results indicate that fast-heating rate (>300 °C/min) promotes the reversion of NA clusters and inhibits re-precipitation of solutes, thereby improving the warm formability. Reversion ageing above 240 °C could induce the formation of coarse η'/η phases, leading to a considerably declined BH response. To accurately predict the strength evolution and deformation behavior during IRAF, a physical-based unified constitutive model was constructed by considering the reversion of NA clusters and solute re-precipitation. The bending and drawing tests on the AA7075-T4 alloy sheets verified that IRAF in the most-reverted state enabled optimum formability. The findings inspire promoting the reversion of pre-existing metastable particles to improve warm formability and post-formed age hardening.