Search

Due to the prominent advantages of low density, high elastic modulus, high specific strength and specific stiffness, cast Al-Li alloys are suitable metallic materials for manufacturing complex large-sized components and are ideal structural materials for aerospace, defense and military industries. On the basis of the microstructural characteristics of cast Al-Li alloys, exploring the role of alloying and micro-alloying can stabilize their dominant position and further expand their application scope. In this review, the development progress of cast Al-Li alloys was summarized comprehensively. According to the latest research highlights, the influence of alloying and heat treatment on the microstructure and mechanical properties was systematically analyzed. The potential methods to improve the alloy performance were concluded. In response to the practical engineering requirements of cast Al-Li alloys, the scientific challenges and future research directions were discussed and prospected.

Ti is regarded as one of the promising grain refiners in cast Al-Li-Cu alloys, but few research works have been done on its independent role. In this study, the effect of Ti on the microstructure evolution and mechanical properties of cast Al-2Li-2Cu-0.5Mg base alloy was investigated. The results revealed that the grains can be prominently refined with the increase of Ti addition. After adding Ti, high density TiB2-Al3Ti composite particles with a low lattice misfit form as heterogeneous nucleation sites for the α-Al matrix. δ′(Al3Li) and T1(Al2CuLi) precipitates that provide enhanced strength are dominated in the alloys after T6 aging treatment. The average size of both δ′ and half-width of δ′-precipitation free zone (PFZ) decreases gradually with the increase of Ti content. This is because the higher binding energy between Ti atoms and vacancies limits the diffusion efficiency of Li atoms, and thus results in a higher ductility. Additionally, no nano-sized Al3Ti or core-shell structure of Al3(Li, Ti) particles are found. The tensile property test results indicate that the Al-2Li-2Cu-0.5Mg alloy achieves optimal properties after aging at 175 °C for 32 h when 0.15wt.% Ti is added. It exhibits a yield strength of 352±5 MPa, an ultimate tensile strength of 423±6 MPa, and an elongation of (3±0.4)%. These findings are expected to offer a reliable theoretical guidance for the industrial composition design of the Al-Li-Cu series cast alloys.

2195 AlLi alloy is being used in the manufacturing of ultra-lightweight external fuel tanks for launch vehicles, but the correlation between the local properties and microstructure of its tungsten inert gas (TIG) welded joint has not been thoroughly investigated. In this work, softening and hardening behaviors of the welded joint are detected through microhardness and tensile tests. Due to the coarse dendritic structure and severe elemental segregation at the grain boundaries, the weld nugget zone (WNZ) is the softest position among the whole joint. A local hardening in the heat affected zone (HAZ) is attributed to the optimal combination of solid solution strengthening brought by the full redissolution of aging precipitates and subsequent precipitation strengthening of the Guinier-Preston (GP) zone. Furthermore, intergranular corrosion (IGC) test shows that severe IGC and sub-grain boundary corrosion (SGC) occurs in the base material (BM), while slight IGC and SGC develops in the HAZ and some pits are left in the WNZ. The corrosion mechanism is proposed to be: In the BM and HAZ, the T1precipitates at the grain boundaries and sub-grain boundaries degrades the IGC and SGC resistance. In the WNZ, large numbers of Cu-rich secondary phases and the anodic dissolution of surrounded Cu-poor α-Al matrix leads to the pitting of the secondary phases.