Corrosion-Electrochemical Behavior of 7075 Aluminum Alloy Laser-Modified with SiC Carbides in Neutral Aqueous Solutions

We establish the influence of the structure of surface layers of aluminum alloy formed as a result of laser modification with silicon carbides on their corrosion-electrochemical behavior in neutral aqueous media. For the laser modification of the surface of 7075 alloy, we use a SiC powder with particle sizes of 80 μm, a hardness of 2600 HV, and a melting point of 2760°С. The SiC powder is blown into the surface layer of the specimens melted by a laser beam in argon. To increase the depth of penetration of solid particles into the surface layers of the alloy, the substrate was heated to 100 and 250°C immediately prior to the laser modification. By the metallographic analysis of the corroded surface, it is established that, unlike the unmodified alloy, where the areas enriched with MgZn2 (Al/MgZn2 galvanic couple) dissolve under the influence of corrosive media, the procedure of modification of 7075 alloy with SiC particles inhibits this process and retards corrosion, as a result of which the sizes and depths of local defects substantially decrease. It is clear that, as a result of modification, we observe the formation of another Al/Al4SiC4 galvanic couple and, hence, corrosion fracture is localized and accompanied by the formation of pits at the sites containing Al4SiC4 inclusions. As a result of potentiodynamic investigations, it is established that the procedure of heating of the substrate to 250°C is less efficient than its heating to 100°C due to a larger volume content of Al4SiC4 inclusions, which play the role of the cause of corrosion damage to the modified layer. It is discovered that, despite the heterogeneity of the modified layer, its corrosion resistance becomes 2–6 times higher depending on the medium.