Eliminating Anisotropy of 7085 Alloy Forgings via Temperature Combination Control During Two-Stage Multi-Directional...

Area of Science:

• Materials Science
• Metallurgy
• Mechanical Engineering

Background:

• 7085 aluminum alloy possesses desirable properties for aerospace applications.
• Large cross-section forgings exhibit significant mechanical anisotropy, particularly in the vertical direction (over 40%).
• This anisotropy limits the effective utilization of 7085 aluminum alloy components.

Purpose of the Study:

• To investigate the effectiveness of two-stage multi-directional forging (MDF) in reducing mechanical anisotropy in 7085 aluminum alloy.
• To compare the microstructural and mechanical property outcomes of isothermal medium-temperature composite MDF (MC-MDF) and isothermal hot MDF (H-MDF).
• To determine if anisotropy reduction can be achieved without sacrificing ultimate tensile strength (UTS).

Main Methods:

• Application of two-stage multi-directional forging (MDF) techniques to 7085 aluminum alloy ingots.
• Utilizing two distinct temperature combinations: isothermal medium-temperature composite MDF (MC-MDF) and isothermal hot MDF (H-MDF).
• Conducting three-dimensional (3D) microstructure analysis and evaluating mechanical properties (UTS, YS, EL).

Main Results:

• MC-MDF successfully reduced anisotropy to below 10% without a significant loss in UTS.
• MC-MDF samples showed increased dislocation density and an enhanced recrystallization structure compared to H-MDF.
• Vertical direction elongation improved significantly, lowering directionality and increasing forging utilization.
• MC-MDF resulted in lower yield strength (YS) but higher work hardening and increased ductility.

Conclusions:

• Isothermal medium-temperature composite MDF (MC-MDF) is a highly effective method for mitigating mechanical anisotropy in 7085 aluminum alloy.
• MC-MDF offers a superior balance of reduced anisotropy, maintained strength, and improved ductility for aerospace forgings.
• The microstructural enhancements, including higher dislocation density and recrystallization, underpin the improved mechanical performance of MC-MDF processed 7085 aluminum alloy.