Effect of Graphite Coating on Microstructure and Corrosion Properties of High Power Diode Laser Surface Melting of 7075 Aluminum Alloy
In this article, a high power diode laser is used for surface melting a 7075-T651 aluminum alloy with and without graphite coating to induce microstructural changes on the surface and to improve corrosion resistance. LSM (Laser Surface Melting) is investigated using 3 kW power with the scan rate of 4 mm/s and 5 mm/s for the graphite coated and non-coated samples in the nitrogen atmosphere respectively. The microstructural analysis observations show that, most of the grain boundaries of the wrought structure and the coarse constituent phase are altered in the re-solidified laser melted layer. The potentiodynamic polarization of the alloy is determined using corrosion study, whereas the electrochemical impedance study is evaluated by treating the alloy in 3.5% sodium chloride solution. Based on this study, it is observed that the corrosion current of the laser treated sample is reduced by 5 times when compared to the un-treated samples. Superior corrosion resistance occurs due to the absence of coursed constituent phases at the surface of the laser-melted layer.
High power diode laser, Graphite coating, Corrosion, Potentiodynamic polarization, Electrochemical impedance.