Influence of Industrial Heat Treatments on the Precipitation Kinetics of an Al-Cu-Mg-Ag-Zr Alloy

Abstract

The impact of different industrial heat treatments on the precipitation kinetics and phase transformation of an Al-Li alloy is studied. AA2195 (Al -1.69 at.% Cu-3.87 at.% Li-0.39 at.% Mg-0.06 at.% Ag-0.04 at.% Zr), a commonly used aluminum alloy, was selected as a model system in this study. Evaluation of the microstructure is performed using differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and field ion microscopy (FIM). Three-dimensional atom probe tomography (APT) was utilized to investigate the intermetallic precipitates in the microstructure after applying T4, T8 and T6 heat treatment tempers. After conducting the T4 heat treatment, β' dispersoids were found to potentially act as nucleation sites for the T 1 phase. The segregation of Li and Cu to the β'/ matrix interface is reported. The microstructure of the samples subjected to the T8 heat treatment exhibit the intersections of different T 1 platelets, which favor a mechanism to hinder the motion of dislocations, resulting in a high hardness value. Growth of the T 1 platelet which proceeds via a ledge mechanism and the dissolution of the θ' phase were observed with increasing aging temperature. After conducting the T6 heat treatment, the microstructure predominantly consists of the T 1 phase. The nucleation of the T 1 platelets on Mg enriched regions that contain localized Ag atoms was observed, suggesting a potential role of Mg to enhance the nucleation of the T 1 phase. Influence of Industrial Heat Treatments on the Precipitation Keywords:Atom probe tomography, Aluminum alloy,Industrial heat treatments, precipitation kinetics Research ArticleOpen Access IntroductionIn response to the demands of various industries for light structural materials, different aluminum lithium alloys have been developed [1]. These alloys are commonly selected because they exhibit an enhanced strength/weight ratio and therefore are typically applied as functional materials with high performance in the aerospace and automobiles industries. Economically, Al-Li alloys are only three times as expensive as conventional aluminum alloys, whereas competing hybrid materials can be up to 10-30 times more expensive [2]. In the context of high fuel prices and fierce competition between composite, hybrid materials and aluminum alloys, different Al-Li-Cu alloys have been developed to overcome most of technical issues associated with the formerly available materials [3]. In the space industry, for instance, Al -Li -Cu based alloys are the candidate material for the construction of launchvehicle liquid-propellant tanks because the ductility and toughness of the alloy are not affected at the lower temperatures. These alloys are known to be strengthened through precipitation hardening and are attracting strong interest in the framework of the development of new alloys, particularly for aerospace components [4]. The current study selects one of the widely used Al-Li-Cu alloys from the Weldalite family [1], namely, the commercial AA2195. This alloy was deve...