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

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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.