Corrosive Properties Of ZK60 Alloy Prepared By Different Processes

The microstructures and the corrosion properties of the as-cast ZK60 (named as ZK60-CT), reciprocating extruded from ZK60-CT (RE-EX-ZK60-CT) and reciprocating extruded from rapidly solidified ZK60 ribbons (RE-EX-ZK60-RS) were sdudied. The corrosion rates of the RE-n-EX-ZK60-RS (n=2, 4, 8 expresses the reciprocating extrusion) alloy in the different NaCl solutions were investigated. Furthermore, the corrosion feature of the RE-n-EX-ZK60-RS alloy was discussed. The microstructure was studied by optical microscope, scanning electronic microscope, X-ray diffraction and transmission electronic microscope. The corrosion rates were investigated with weight loss method and the corrosion current densities were calculated with Tafel lines according to the polarization curves. The expansive process of the pit corrosion was recorded by optical microscope, the corrosion micro-morphologies were observed by scanning electronic microscope. Some results were concluded.The grains of the ZK60-CT alloy are coarse and the eutectic microstructure distributes as network, the grains of the ZK60-CT alloy are refined during the reciprocating extrusion, the microstructure of the RE-EX-ZK60-RS alloy is uniform with refined grain matrix. The corrosion rates of the ZK60-CT alloy, RE-EX-ZK60-CT alloy, RE-EX-ZK60-RS alloy prepared by different processes are different. With weight loss, the corrosion rate of the RE-EX-ZK60-RS alloy is the highest, the corrosion resistance of the ZK60-CT alloy is the best. According to the polarization curves, the corrosion potential of the RE-EX-ZK60-RS alloy is the highest and the corrosion current density is the lowest. The feature in microstructure of the RE-EX-ZK60-RS alloy is that the refined second phase particles precipitate during the reciprocating extrusion, and because of the feature, the corrosion resistance of the RE-EX-ZK60-RS alloy decreases.So, the corrosion resistance of the material couldn't be improved although the mechanical properties can be improved by the srenghen of the precipitated phase particles. However the undermining of the RE-n-EX-ZK60-RS alloy with refined grains in lagre area is not found.The more passes of reciprocating extrusion, the microstructure of the RE-n-EX-ZK60-RS alloy gets more uniform. With weight loss, the RE-n-EX-ZK60-RS alloy exhibits decrease in corrosion rate with increase in pH and increase in corrosion rate with increase in chloride ion concentration. With the increase in pH, the polarization curves of the RE-n-EX-ZK60-RS alloy shift to positive values, the corrosion potential gets higher and the corrosion current density gets lower; with the increase in chloride ion concentration, the polarization curves shift to negative values, the corrosion potential gets lower and the corrosion current density gets higher.