Study on hardenability of 2050 Al–Cu–Li alloy ultra-thick plate

Abstract

The hardenability of the 2050 Al–Li alloy ultra-thick plate was evaluated by end quenching and interrupted quench methods. Microstructural investigation at different thickness positions after quenching and aging were conducted using optical microscopy, scanning electron microscope, and transmission electron microscope. The factors affecting the hardenability were discussed in combination with cooling rate and composition examination using energy dispersive spectroscopy. The results indicated that the tensile strength of different thickness positions decreased as the distance from the quenching end increases. Coarse Cu-rich phase particles, formed at the grain and grain boundaries during the end quenching process, lead to solute depletion around the grain boundaries, causing a precipitate-free zone. This zone obstructs the formation of the T1 phase, thereby reducing strength. At identical distances from the quenching end, the tensile strength at the mid-thickness (T/2) location consistently exceeds that at the quarter-thickness (T/4) location. This is due to the original microstructural differences, where the T/2 position experiences a slower cooling rate, has a lower copper content, and shows an increase in the number but a decrease in the size of precipitated coarse Cu-rich phase particles from the supersaturated solution, with the solute consumption remaining relatively constant. Consequently, the tensile strength variation at equal distances from the quenching end is minimal.

Keywords

• 2050 Al–Cu–Li alloys
• Thick plate
• Hardenability
• Microstructure
• TTP curve