High solid-solution strengthening mechanism of a novel aluminum-lithium alloy fabricated by electromagnetic near-net shape technology

Abstract

The microstructure evolution and precipitation strengthening behavior of Al–Li alloy manufactured by traditional casting, twin-roll casting (TRC) and electromagnetic twin-roll casting (E-TRC) were systematically investigated. The results show that the high cooling rate of the TRC process makes more alloying elements dissolve in the α(Al) matrix and improve the supersaturated solid solubility of the alloy. However, the application of the electromagnetic oscillation field (EOF) in the TRC process not only raises the undercooling of the alloy and increases the effective distribution coefficient Ke of the solute but also enhances the mixing capability and diffusion ability of the solute atoms and inhibit the recrystallization of deformed microstructure. On the one hand, the EOF reduces macro-segregation and refines the solidified microstructure of alloys. On the other hand, E-TRC increases the intragranular solid-solution capacity of the solute and effectively increases the intragranular solid-solution amount of solute elements in the α(Al) matrix. The higher the degree of supersaturated solid-solution, the greater the precipitation driving force of precipitates in the aging process, hence after the same heat treatment procedures, there are more volume fraction and finer strengthening phases such as T1 (Al2CuLi) phase and δ′ (Al3Li) phase precipitates in the E-TRC alloy, the aging strengthening effect is greatly improved, and the strength of the Al–Li alloy is significantly increased.