Grain Refinement and Thermal Stability of 2219 Aluminum Alloy in the Warm Deformation Process

Abstract

2219 Al alloy is an important material for manufacturing launch vehicles, and its grain structure has a substantial effect on the performance of storage tank transition rings. In this work, warm compression tests (100–350 °C) of 2219 Al alloy were carried out, a grain refinement model of warm deformation was established, and the evolution and thermal stability of the static recrystallized grain size D were analyzed. The results showed that static recrystallization is the main mechanism of grain refinement, and that the nucleation rate and grain refining effects were significantly improved by decreasing the deformation temperatures (T). The established model was found to be accurate, and the predicted and experimental values exhibited high degrees of coincidence. When T and the amount of deformation (Δd) were respectively 150 °C and 70%, the value of D was reduced from 60 μm to 21 μm. Additionally, when the solution treatment time was increased from 0 to 4 h, there was a slight change in the values of D (high thermal stability) when T was lower than 250 °C and Δd was greater than 20%, but they significantly increased when Δd was less than 10%. In this paper, the effects of different deformation temperatures T and deformation amount Δd on average grain size D of 2219 Al alloy forgings were investigated, and the evolution rule and thermal stability of D were analyzed. The research results showed that static recrystallization was the main mechanism for grain refinement of 2219 forgings, and the nucleation rate and grain refining effects were improved by increasing Δd and decreasing T. Warm compression was conducive to accumulating higher-density dislocations, storing more deformation energy, generating more high energy distortion points. Hence, increasing the recrystallization nucleation rate and decreasing grains growth velocity. Furthermore, the thermal stability of grain sizes increased with the decreasing recrystallization grain size and uniformity. Because there is a low energy difference between fine and uniform grains (the interface energy was very low), which led to slow grain boundary migration speed and restraining grain growth even at high temperatures.