Mechanical Properties and Microstructure Evolution of Al-Li Alloy Under the PHF Process

Area of Science:

• Materials Science
• Metallurgy
• Aerospace Engineering

Background:

• Aluminum-lithium (Al-Li) alloys are crucial in aerospace due to their superior mechanical properties.
• Traditional thermomechanical treatments for Al-Li alloys are lengthy and require optimization.
• Developing efficient processing methods is vital for advancing Al-Li alloy applications.

Purpose of the Study:

• To introduce and evaluate a novel pre-strain and pre-aged hardening warm forming (PHF) process for Al-Li alloys.
• To investigate the influence of pre-strain, pre-aging, and warm forming parameters on microstructure and mechanical properties.
• To establish a shorter, more efficient thermomechanical treatment cycle for Al-Li alloys.

Main Methods:

• Implementation of a multi-stage process involving pre-strain, pre-aging, and warm forming.
• Macro-control of multiphase precipitation and phase transformation through controlled process stages.
• Microstructural analysis to observe phase evolution, particularly T1, δ', and θ' phases.
• Tensile and yield strength testing to evaluate mechanical performance.

Main Results:

• The optimal PHF process parameters for 2A97 Al-Li alloy were identified as 7% pre-strain, 80 °C/16 h pre-aging, and 250 °C/10 min warm forming.
• This specific process yielded optimal tensile and yield strengths of 565.3 MPa and 531.2 MPa, respectively.
• Pre-strain promoted T1 phase nucleation and dynamic recrystallization, while a 10-minute warm-maintaining time ensured fine, uniform T1 precipitates.

Conclusions:

• The proposed PHF process effectively refines the microstructure and enhances the mechanical strength of Al-Li alloys.
• Pre-strain plays a critical role in facilitating beneficial phase transformations and recrystallization during warm forming.
• This innovative short-process forming method offers significant advantages over traditional long thermomechanical treatments for Al-Li alloys.