1. Mihael Bučko, University of Defense, Military Academy, , Serbia
2. Marija Mitrović, University of East Sarajevo, Faculty of Technology, Republic of Srpska, Bosnia and Herzegovina
3. Milorad Tomić, University of East Sarajevo, Faculty of Technology, Republic of Srpska, Bosnia and Herzegovina
4. Jelena Bajat, University of Belgrade, Faculty of Technology and Metallurgy, , Serbia
In this work Zn-Mn-Al2O3 composite coatings electrodeposited on steel were studied. The influence of Zn2+/Mn2+ ion ratio in the plating solution (1:1, 1:2 and 2:1), deposition current density (1-4 A dm–2), size of alumina particles (300 nm and 10 μm) and type of agitation (magnetic stirring and ultrasound) on morphology and corrosion stability were examined and compared. Composite coatings were deposited from additive-free chloride-based plating baths. In order to avoid agglomeration after alumina addition in the plating baths, the suspension was intensively agitated by a magnetic stirrer (200 rpm) for at least 2 h at room temperature before the codeposition experiments and during deposition either magnetic stirring (200 rpm) or ultrasound (38.7 W cm3 power) were used. The corrosion behaviour of Zn-Mn-Al2O3 composite coatings electrodposited at different parameters was evaluated by polaryzation measurements and electrochemical impedance spectroscopy in 3% NaCl solution. Morphology and chemical content was determined by SEM-EDS measurements. The high current efficiency of over 90% was achieved in all plating solutions containing 10 μm particles. The highest amount of Mn and Al2O3 were incorporated in composite alloy deposited from solution with Zn2+/Mn2+ ion ratio of 1:1. These coatings also showed homogenous morphology and greatest corrosion stability so they were chosen for further analysis of the influence of particle size and stirring type. Incorporation of 300 nm alumina particles in plating bath resulted in higher amounts of both Mn and Al2O3 in composite coatings. In addition, more homogenous coatings morphology and improved corrosion stability were obtained, with most optimal deposition current density of 4 A dm–2. Current efficiency remained high when magnetic stirring was used for agitation and somewhat dropped upon utilization of ultrasound. However, the composite coatings deposited with mechanical stirring also showed a high degree of agglomeration of alumina particles on top of the coating. In contrast, the uniform particles distribution was achieved by using ultrasonic agitation. Besides, considerable higher corrosion resistance was achieved by ultrasound assisted electrodeposition. Based on all results the highest corrosion stability, determined by both the smallest corrosion current density and the greatest low frequency impedance modulus values, were obtained by deposition from bath with 300 nm particles at current density of 4 A dm–2 and deposited with ultrasound aggitation.
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