Preparation and properties of plasma sprayed NiAl10 and NiAl40 coatings on AZ91 substrate

Magnesium alloys are, due to high specific strength and stiffness, materials suitable for lightweight applications in automotive and aeronautical industries. Very poor corrosion resistance of magnesium and magnesium alloys significantly limits their wide utilization. Magnesium alloys are very susceptible to galvanic corrosion that can result in serious pitting corrosion, particularly in wet and salty environment. Magnesium and its alloys can be protected by formation of protective surface layers which can be achieved by plasma spraying capable of preparing metal and/or ceramic coatings. In this work, plasma coatings of NiAl10 and NiAl40 on AZ91 magnesium alloy substrate were prepared by the hybrid plasma spraying system WSP®-H 500. Present results show a significant effect of the preheat temperature of the AZ91 substrate during plasma spraying on development of a diffusion bonding due to the formation of sub-layer composed of Mg3AlNi2, Al12Mg17 phases and of Mg and Al solid solutions. The plasma sprayed coatings were observed by scanning electron microscope with elements point analysis and by X-ray phase analysis. The mechanical properties of prepared coatings were evaluated by adhesion tests. The corrosion resistance of prepared coatings was evaluated using the method of potentiodynamic measurements performed in the 0.5 mol·l− 1 NaCl solution while the long-term corrosion resistance was assessed in condensation chamber in wet air atmosphere at the temperature of 35 °C. Both the tests showed significant effect of present sub-layers on resulting corrosion resistance.