Abstract
Al-Li based alloys are attractive materials for the aerospace industry. The twin-roll casting of such materials could provide properties not achievable by conventional direct-chill casting and downstream processing methods due to significantly higher solidification rates. An Al-Li-Cu-Mg-Zr alloy was twin-roll cast with the same alloy containing a small addition of Sc. The microstructure of as-cast materials and the influence of Sc on the behavior of the alloy at elevated temperatures were studied by means of light and electron microscopy and by resistivity measurements. A fine-grained structure was formed during twin-roll casting, but several surface and internal defects were found on the strips, which should be suppressed by a further adjustment of the casting conditions. The addition of Sc had a positive effect on grain size uniformity and microstructure stabilization at elevated temperatures, as shown by the precipitation of a fine dispersion of coherent Sc- and Zr-containing precipitates.
Highlights
Al-Li alloys have found increasing use in weight and stiffness critical structures for aircraft and aerospace applications as they have better properties than structures made of commercial Al alloys [1,2,3,4]
The superior properties of Al-Li alloys are mainly attributed to the added Li, which influences the weight reduction and elastic modulus
One wt.% of Li reduces the density of the resulting Al alloy by approximately 3% and increases the elastic modulus by approximately 6% [4,5]
Summary
Al-Li alloys have found increasing use in weight and stiffness critical structures for aircraft and aerospace applications as they have better properties (low density and high specific strength) than structures made of commercial Al alloys [1,2,3,4]. The superior properties of Al-Li alloys are mainly attributed to the added Li, which influences the weight reduction and elastic modulus. The addition of Li to Al produces fine precipitates, which improve the stiffness and strength of the Al alloys [6]. These aspects make Li the optimum metallic element for Al alloys used in the aircraft industry. The main strengthening in Al-Li alloys is generally due to a huge volume fraction of the Al3 Li (δ’) phase, which is the main reason for the high elastic modulus observed in these alloys, since Al3 Li itself has a large intrinsic modulus [3,4,9]
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