Analysis and Characterization on Dynamic Recrystallization in Casting AZ31 Mg Alloys Under Plane Strain Compression

Area of Science:

• Materials Science
• Metallurgy
• Mechanical Engineering

Background:

• Twinning and dynamic recrystallization are critical for the mechanical properties of magnesium (Mg) alloys.
• Understanding these phenomena is essential for improving the strength and formability of coarse-grained Mg alloys under severe plastic deformation.

Purpose of the Study:

• To investigate the influence of strain rate and temperature on twinning and twin-induced dynamic recrystallization (TDRX) in AZ31 Mg alloys.
• To characterize the relationship between TDRX, stress concentration, and microstructural evolution near crack boundaries.

Main Methods:

• Plane strain compression tests were performed on casting AZ31 Mg alloy samples.
• Electron backscatter diffraction (EBSD) was used to analyze twinning and recrystallization behaviors.
• Microstructural characterization was conducted near and away from crack boundaries.

Main Results:

• Increased strain rates significantly promote extension twinning and TDRX, especially near crack tips due to stress concentration, indicating positive strain-rate sensitivity.
• TDRX is stress-favored and temperature-dependent, but not directly proportional to temperature.
• 300°C was found to be more beneficial for TDRX than 400°C, leading to improved strength and plastic deformability.

Conclusions:

• Higher strain rates and lower temperatures (300°C) enhance TDRX by increasing strain-hardening rate and flow stress, facilitating the transformation to fine twin-walled grains.
• Stress-favored TDRX is crucial for grain refinement and sustained plastic deformation in coarse-grained AZ31 Mg alloys.
• Optimizing TDRX conditions is key to enhancing the performance of Mg alloys in severe plastic deformation applications.