Hardness and corrosion resistance of Zn−Mn/Al2O3 composite coatings produced by electrochemical deposition

Abstract

The aim of this study is development and characterization of the novel Zn-Mn/Al2O3 composite coatings. The coatingswere electrodeposited with constant current density on steel, from chloride solution, without any commercial additives. TheZn−Mn alloy coatings that show high corrosion resistance, may be used in future as an alternative to cadmium coatings.However, the pure Zn and Zn alloy coatings are characterized with poor mechanical properties. Therefore, in this work thealumina particles were incorporated into the Zn-Mn matrix, and the hardness and corrosion resistance of the obtainedcomposite coatings were tested. The mechanical and ultrasound agitation were used to achieve good dispersion of platingsolution and homogeneous co-deposition of second phase. The goal was to examine the effect of the agitation type in bath,on the attributes of the deposited composite coatings. The incorporation of Al2O3 particles was enhanced when themechanical agitation of the solution was applied. However, in case that this agitation method was used, the agglomeration ofthe alumina particles occurred. In contrast, when an ultrasonic agitation of the plating solution was applied, the uniformdistribution of the alumina particles could be achieved. The presence of particles in the matrix, along with appliedultrasound, resulted in grain refinement and homogeneous microstructure. The Al2O3 nanoparticles incorporated in Zn-Mnalloy matrix, resulted in a significant increment in the indentation hardness and a modest increase in the coating corrosionresistance. However, the coating hardness increased with alumina addition, only in case when an ultrasonic agitation of theelectrodeposition solution was used.