Microstructure specific process chain design for the manufacturing of Al-Li-strips by means of twin-roll casting

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Al-Li alloys are attractive for aircraft and aerospace applications because their properties are superior to those of conventional Al alloys. Their exceptional properties are attributed to the formation of a finely dispersed non-equilibrium Li-rich phase in the Al-matrix. The main issue of Al-Li alloys is an anisotropic behaviour accompanied by a limited formability. The main reasons for this are the specific features of the strengthening phases, the grain microstructure and the crystallographic texture, which are formed during direct chill or mould casting and subsequent thermomechanical processing (TMP). Since the potential of conventionally prepared alloys is limited, methods of alloy chemistry adaptation, novel casting and TMP techniques have to be applied to improve the formability of Al-Li alloys while maintaining their high specific strength. Precipitates rich in Mg and Cu further strengthen the Al-Li alloy, while the fine-grained microstructure will be stabilised by precipitates of Sc and Zr containing particles. The combination of twin-roll casting (TRC) and TMP - including hot asymmetric rolling - will be used to provide a macroscopic homogeneous distribution of alloying elements in a supersaturated Al-matrix, to create a beneficial crystallographic texture, to engineer the grain microstructure and the size and morphology of the precipitates, and to enhance the formability of the material. The main objective of the project is to establish correlations between the processing conditions during TRC and the subsequent TMP of thin strips of high-strength Al-Li-Mg-Cu-Sc-Zr alloys and their microstructural characteristics as well as the mechanical properties.