Laser surface alloying of an Mg alloy with Al + Mn to improve corrosion resistance

Abstract

In the present study, an attempt has been made to enhance the corrosion resistance of a Mg alloy (MEZ) by laser surface alloying with Al + Mn. Laser surface alloying has been carried out with a 10 kW continuous wave CO₂ laser by melting and simultaneous feeding of a powder mixture of Al and Mn in the ratio of 3 : 1 and 1 : 3, respectively. Following laser irradiation, the alloyed zone has been characterized by a detailed microstructural observation and phase analysis. Moreover, the properties of the surface alloyed layer like microhardness and corrosion have been evaluated in detail. The surface modified layer predominantly consists of dendrites of Al + Mn and Al + Mg. The microhardness of the alloyed zone has been significantly enhanced to as high as 250-350 VHN as compared to 35 VHN of the substrate region. The corrosion rate in a 3.56 wt.% NaCl solution has significantly reduced to 250 mpy for laser surface alloyed specimen as compared to 1520 mpy of the MEZ substrate. The enhanced corrosion resistance was attributed to the presence of Al₂O₃ and Mn₃O₄ oxide layer on the surface.