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Studies of Defects in Laser Surface Treated Magnesium And Its Alloy
J. Dutta Majumdar, P. Mishra, D. Das, B.L. Mordike and I. Manna

Among the light metals, Mg and its alloys occupy a prominent position due to its low density, excellent machine-ability and high specific strength. However, a relatively poor resistance to corrosion and wear are serious impediments against a wider application of Mg alloys. To improve the wear and corrosion resistance, laser surface melting and alloying (with Al and Mn) of a commercial Mg alloy, MEZ (Zn 0.5%, Mn 0.1%, Zr 0.1%, rare earth elements 2%, Mg rest) were carried out with a 10 kW continuous wave CO2 laser. The formation of various point defects due to the rapid quenching associated with laser surface engineering may cause a deterioration of physical and electrochemical properties of the laser treated components. Dislocations, may be detected by transmission electron microscopy, but it is extremely difficult to identify point defects such as vacancies or their agglomeration, the density of which is more prone to vary with laser parameters. In the present study, a detailed investigation of the nature and extent of point defects have been carried out by positron annihilation lifetime spectroscopy. The defect characteristics of the alloyed zone have been correlated with the microstructure and phases of the surface modified layer. Finally, the microhardness of the surface modified layer was studied in detail.

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