Dual wavelength laser beam alloying of aluminum alloy for enhanced corrosion resistance

Aluminum alloys are known for their poor resistance to localized attack and, in particular, for pitting in chloride-containing electrolytes. In this paper, improvement of the pitting corrosion resistance of 2014-T6 aluminum alloy has been investigated by means of laser surface alloying of Cr into the substrate. Since aluminum is a highly reflective and thermally conductive material, it is often difficult to process with laser beams. Oxide films on the surface can prevent surface alloying as with the case of Cr alloying into aluminum by in-situ powder feeding. This work describes a new technique using mixed excimer laser and CO2 laser beam processing to generate a Cr alloyed layer on a 2014 aluminum alloy substrate. It is shown that improvement of alloying homogeneity following in-situ powder feeding can be achieved with mixed beam processing. Conditions under which this can be achieved have been studied and the effect of laser processing parameters on the surface roughness, oxidation and absorption is discussed. Microstructural and surface morphological analysis using optical microscopy, scanning electron microscopy and energy dispersive spectroscopy are also discussed. The electrochemical behavior of the treated samples in de-aerated 1 m NaCl solution has also been studied and has indicated that an improvement of pitting resistance by laser surface treatment can be achieved.