Annealing Behavior of a Mg-Y-Zn-Al Alloy Processed by Rapidly Solidified Ribbon Consolidation

Area of Science:

• Materials Science
• Metallurgy
• Solid State Physics

Background:

• Mg-Y-Zn-Al alloys processed by rapidly solidified ribbon consolidation (RSRC) are promising for structural applications.
• Their mechanical strength is linked to solute-enriched stacking faults (SESFs), forming cluster-arranged layers (CALs), cluster-arranged nanoplates (CANaPs), or long-period stacking ordered (LPSO) phases.
• The thermal stability of these solute arrangements is critical for high-temperature mechanical performance.

Purpose of the Study:

• To investigate the structural evolution of an RSRC-processed Mg-0.9%Zn-2.05%Y-0.15%Al alloy during annealing near its melting point.
• To understand the influence of thermal treatment on solute arrangements and phase stability.
• To correlate microstructural changes with mechanical properties at elevated temperatures.

Main Methods:

• In situ synchrotron X-ray diffraction (XRD) was used to monitor structural changes during heating up to 833 K at 0.666 K/s.
• Ex situ electron microscopy (before and after annealing) provided complementary microstructural analysis.
• Analysis of matrix lattice constant ratio (c/a) and secondary phase XRD intensity.

Main Results:

• A significant decrease in the matrix lattice constant ratio (c/a) was observed above 753 K, attributed to partial melting in solute-rich regions.
• The decreased c/a ratio was restored upon cooling, indicating a reversible process.
• An increase in secondary phase XRD intensity during cooling suggested long-range ordering of the solute-enriched phase.
• Electron microscopy revealed coarsening of both matrix grains and solute-enriched particles after heat treatment.

Conclusions:

• Partial melting and subsequent solute re-ordering significantly influence the structure of RSRC-processed Mg-Y-Zn-Al alloys at high temperatures.
• The observed changes in lattice parameters and phase evolution provide insights into the thermal stability limitations for structural applications.
• Understanding these high-temperature behaviors is crucial for optimizing alloy design and processing for demanding environments.