Machinability study of aluminum-lithium alloys for aerospace applications: influences of heat treatments and machining conditions

Abstract

This thesis investigates the machinability of advanced aluminum-lithium alloys (Al-Li, Al-Li- Cu, and Al-Li-Cu-Sc), prized for their low density, high tensile strength, and corrosion resistance, making them essential for aerospace applications. However, machining challenges such as reducing the surface roughness, the cutting forces and the fine metallic particles emissions remain critical concerns. This study provides a detailed analysis of how alloy composition, heat treatments, and machining parameters affect these challenges. This study thus fills a crucial gap in the literature by focusing on the effects of scandium and copper additions to Al-Li alloys and their effects on heat treatments and machinability. Heat treatments were optimized for each alloy to achieve the highest hardness, with the Al-Li alloy reaching 97 HV under 580 °C/1 h solution treatment + 150 °C/45 h artificial aging, and the Al-Li-Cu and Al-Li-Cu-Sc alloys reaching 164 HV and 182.7 HV, respectively, under 505 °C/5 h solution treatment + 180 °C/20 h artificial aging. End milling experiments were conducted at constant depth of cut (2 mm) under both wet and dry conditions, varying feed rates (0.05–0.15 mm/th) and cutting speeds (200–600 m/min). Key findings demonstrate that the Al-Li alloy required the lowest machining force (52.3 N), while Al-Li-Cu and Al-Li-Cu-Sc alloys required 90 N and 67 N, respectively. Cutting forces decreased with higher cutting speeds and increased with higher feed rates for all alloys. The use of cutting fluid significantly enhanced the surface finish of Al-Li (by 32.2%) and reduced cutting forces in Al-Li-Cu-Sc (by 26.6%), although it had minimal effect on Al-Li-Cu. Particle emissions during machining were primarily influenced by cutting speed, followed by alloy hardness and feed rate. The Al-Li-Cu-Sc alloy, despite its high hardness, demonstrated superior machinability due to refined microstructure enabled by scandium additions. The findings highlight the importance of optimized heat treatments and improving machining parameters in developing lightweight, high-strength materials for aerospace components with superior surface quality and machining precision.

Date	19 Dec 2024
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Victor Songmene (Supervisor) & Samuel Fawzy Hosny (Co-supervisor)