Evolution of micropores and second phases during hot deformation of 2050 Al-Li alloy

Abstract

Microporosity and second phases are typical components for casting 2050 alloy. In this paper, the evolution of both microporosity and the second phases during hot deformation of casting 2050 Al-Li alloy was studied. Firstly, based on industrial CT technology, the typical morphology characteristics of micropores during the hot deformation process of the alloy were studied and related statistics were carried out. The results show that with the increase of deformation strain, the volume, volume ratio, and porosity of the micropores gradually decreased, and the roundness gradually increased. Secondly, the detailed evolution mechanism of the second phases during hot deformation was studied by SEM, XRD, and TEM. It was found that with the increase of deformation strain, the thin plate T1 phase gradually undergoes shearing and exhibits bend-shaped morphology in the SEM image, which was essentially a process of stress transfer from Al matrix to the T1 phase. Meanwhile, the T1 phase also experienced thinning and secondary precipitation. This is mainly attributed to the intensive interaction between the alloying elements within T1 phase and the dislocations pile-up around T1 phase during the hot deformation process. While for the large-size intermetallic phase AlCuFeMn, it breaks up gradually and oxide inclusion is generated at the broken site, which provides favorable conditions for the initiation and propagation of cracks during hot deformation. From TEM observation, it is found that there is Al6Mn intermetallic phase in the alloy matrix with different morphologies under different deformation strains. When the deformation strain reaches 70%, a large number of nanometer Al6Mn particles are dynamically precipitated near the dislocations.