Investigation into the impact of phase composition on the thermal expansion and mechanical properties of Al–Cu–Li alloys

Abstract

The study employed high-temperature X-ray diffraction, quantitative phase analysis, and tensile mechanical property measurements to investigate the relationship between coefficient of thermal expansion (CTE) and phase composition, along with the average yield strengths and Young's moduli of Al–Cu–Li alloys in three different sheet orientations: 1441, V-1461, V-1469, V-1480, and V-1481. The copper content within the solid solution and the mass fractions of the T1(Al2CuLi) and δ′(Al3Li) phases were determined using an innovative technique based on measuring the lattice distance of the α solid solution, Vegard's law, and balance equations for the elemental and phase compositions of the alloys. It was observed that as the lithium-to-copper ratio in the alloys increased from 0.32 to 1.12, the proportion of the δ′(Al3Li) phase increases from 6.3–8.4 wt.% in V-1481, V-1480 and V-1469 alloys to 16.0–17.3 wt.% in 1441 and V-1461 alloys, accompanied by a decrease in the T1(Al2CuLi) phase from 5 to 1 wt.%. This led to an increase in the Young's modulus from 75 to 77 GPa due to higher overall proportion of intermetallic compounds and a reduction in yield strength from 509 to 367 MPa due to the decrease in the T1 phase. This decrease in yield strength resulted from the fact that the hardening effect of the T1 phase was 3–4 times greater than that of the δ′ phase, and this couldn't be offset by an increase in the total intermetallic compound proportion. The observed increase in Young's modulus indicated that the elastic properties of the intermetallic phases were similar, and the rise in the total fraction of intermetallic compounds compensated for the decrease in the T1 phase. Furthermore, it was demonstrated that СTE, as measured based on the thermal expansion of the solid solution, also depended on the characteristics of the intermetallic phases present in the alloy. This expanded the potential interpretations of СTE measurement results.