Abnormal Twinning Behavior Induced by Local Stress in Magnesium

Area of Science:

• Materials Science
• Metallurgy
• Crystallography

Background:

• AZ31 alloy is a widely used magnesium alloy.
• Twinning is a critical deformation mechanism in magnesium alloys.
• Understanding twinning behavior is essential for predicting alloy performance.

Purpose of the Study:

• To investigate the influence of compressive strain on twinning behavior in rolled AZ31 alloy.
• To analyze the factors controlling twin nucleation and growth.
• To elucidate the role of local stress and surrounding grains in the twinning process.

Main Methods:

• Uniaxial compression tests on polycrystalline AZ31 alloy (30 μm grain size).
• In situ electron backscattered diffraction (EBSD) for microstructure evolution.
• Analysis of kernel average misorientation (KAM) and Schmid factor (SF).

Main Results:

• Observed multiple primary twin variants and extension double twins within the same grain.
• Twin nucleation is influenced by both the Schmid factor and surrounding grain interactions.
• Existing primary twins alter local strain distribution, promoting secondary twin nucleation and primary twin growth.
• Simultaneous primary twin growth and secondary twin nucleation occur for strain accommodation.

Conclusions:

• Twinning in AZ31 alloy is governed by a combination of Schmid factor, intergranular strain accommodation, and local stress variations.
• Local stress exceeding the critical resolved shear stress (CRSS) is a key factor for twin nucleation.
• Twinning acts as a response to local stress states rather than solely the applied stress.