Gradient Microstructure Induced by Surface Mechanical Attrition Treatment (SMAT) in Magnesium Studied Using Positron...

Area of Science:

• Materials Science
• Surface Engineering
• Corrosion Science

Background:

• Magnesium alloys are susceptible to corrosion.
• Surface modification techniques can improve material properties.
• Understanding subsurface microstructural changes is crucial for material performance.

Purpose of the Study:

• To investigate the effects of Surface Mechanical Attrition Treatment (SMAT) on the microstructure and properties of commercial grade magnesium.
• To correlate microstructural changes with hardness and corrosion behavior.
• To analyze defect evolution using positron annihilation spectroscopy.

Main Methods:

• Surface Mechanical Attrition Treatment (SMAT) was applied to commercial grade magnesium.
• Characterization involved positron annihilation lifetime spectroscopy, variable energy positron beam measurements, microhardness testing, electron backscatter diffraction, X-ray diffraction, and electrochemical corrosion tests.

Main Results:

• SMAT induced a gradient microstructure with increased dislocation density and grain refinement, leading to higher subsurface hardness.
• Positron lifetime analysis indicated positron trapping in vacancies associated with dislocations.
• Electrochemical tests showed increased susceptibility to anodic oxidation, enhanced hydroxide formation, and reduced corrosion current.
• Residual stress was not significantly affected by the SMAT duration or vibration amplitude.

Conclusions:

• SMAT effectively modifies the subsurface microstructure of magnesium, enhancing hardness.
• The induced microstructure alters the corrosion mechanism, improving surface protection and reducing corrosion rates.
• Positron annihilation spectroscopy provides insights into defect evolution and its correlation with mechanical and electrochemical properties.