Creep aging in aluminum-copper alloys – Interrelations between precipitate characteristics, monotonic behavior and fatigue properties

在过去的几十年里，对轻质材料的需求不断增长，以及制造专门满足任何给定强度要求的部件的需求，促使研究人员和科学家将铝合金应用于各种工业应用。铝合金具有优异的室温强度密度比、高断裂韧性和耐腐蚀性，在航空航天、交通运输和汽车工业中得到了广泛的应用。多年来，研究人员一直致力于通过使用各种热机械工艺路线来提高合金的强度。由于这种热处理工艺提供的部件具有高强度和足够好的延展性，因此重点仍然放在沉淀硬化/时效上。沉淀硬化还可以提高合金的断裂韧性。虽然常规时效已经使用了几十年，但蠕变/应力时效直到最近才引起人们的广泛关注。蠕变时效是人工时效和塑性变形的结合，可以同时达到所需程度的塑性变形和沉淀硬化。因此，这种方法在许多实际应用中显示出了巨大的潜力。分析了蠕变时效对铝合金组织发展和力学性能的影响。然而，目前对铝合金蠕变时效各方面的数据和认识还很缺乏。蠕变时效后的析出组织如何依赖于热机械工艺参数，蠕变时效过程中的析出动力学如何取决于热机械工艺参数，合金元素如何影响蠕变时效行为，以及d)蠕变时效铝合金的单调和循环力学性能如何影响尚不清楚。本项目的目的是深入了解铝合金蠕变时效的机理及其对最终力学性能的影响，并通过基于模型的评估来促进理解。与其他依靠析出强化的合金相比，在类似蠕变时效的加载条件下，容易发生组织变化。

In the past decades, the growing demand for lightweight materials and the need to manufacture components that specifically meet any given strength requirements have motivated researchers and scientists to qualify aluminum alloys for numerous industrial applications. Due to the exceptional strength-to-density ratio at room temperature, high fracture toughness and corrosion resistance, aluminum alloys are used extensively in the aerospace, transportation and automotive industries. For many years, researchers have endeavored to improve the strength of alloys through the use of various thermomechanical process routes. The focus remains on precipitation hardening / aging due to the fact that this heat treatment process provides components with high strength and sufficiently good ductility. Precipitation hardening can also improve the fracture toughness of alloys. Although conventional aging has been in use for decades, it is only recently that creep / stress aging has attracted significant attention. Creep aging is a combination of artificial aging and plastic deformation, making it possible to achieve the necessary degree of plastic deformation and precipitation hardening at the same time. Thus, this approach shows great potential for many practical applications. Studies carried out so far analyzed the influence of creep aging on the microstructural development and the mechanical properties of aluminum alloys. However, there is a significant lack of data and understanding on various aspects related to creep aging of aluminum alloys. It remains unclear how a) the precipitation structure after creep aging depends on thermomechanical process parameters, b) the precipitation kinetics during creep aging depend on thermomechanical process parameters, c) alloying elements influence the creep aging behavior and d) the monotonic and cyclical mechanical properties of creep-aged aluminum alloys are affected. The aim of the present project is to gain a profound understanding of the mechanisms involved in creep aging of aluminum alloys and their effects on the final mechanical properties as well as to foster understanding by model based assessment, i.a. with reference to other alloys relying on precipitation strengthening being prone to changes of microstructure under loading conditions similar to creep aging.