Optimizing Thermomechanical Processing for Producing Bulk Fine-Grained Aluminum Alloy with Thermal Stability

Area of Science:

• Materials Science
• Metallurgy
• Physical Metallurgy

Background:

• Fine-grained metallic structures offer enhanced mechanical properties.
• Achieving and maintaining fine grains under thermal stress is a significant challenge.
• Aluminum alloys with scandium and zirconium exhibit potential for high-temperature applications.

Purpose of the Study:

• To evaluate the thermal stability of fine-grained Al-0.1Sc-0.1Zr alloy produced by severe plastic deformation (SPD).
• To compare the effects of different SPD routes (Bc and C) and aging sequences (pre- and post-ECAP) on microstructure and thermal stability.
• To identify the microstructural features responsible for thermal stability.

Main Methods:

• Bulk Al-0.1Sc-0.1Zr alloy preparation.
• Equal channel angular pressing (ECAP) using routes Bc and C.
• Aging treatment applied before and after ECAP.
• Electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) for microstructural analysis.
• Thermal stability testing at 450 °C for 10 hours.

Main Results:

• All tested microstructures exhibited excellent thermal stability, maintaining mean grain sizes below 5 μm after thermal exposure.
• Nano Al₃(Sc,Zr) precipitates were identified as key pinning structures, preventing grain growth.
• ECAP route Bc resulted in more stable high-angle grain boundaries (HAGBs) compared to route C.
• Similar microstructural outcomes were observed regardless of whether aging preceded or followed ECAP.

Conclusions:

• The combination of SPD and nano-precipitates provides exceptional thermal stability in Al-Sc-Zr alloys.
• The choice of ECAP route influences grain boundary stability, with Bc being superior.
• The processing route offers flexibility for tailoring microstructures for specific applications without compromising thermal stability.