EFFECT OF COATING THICKNESS ON CORROSION PROPERTIES OF PLASMA SPRAYED ALUMINA COATED AZ31B MAGNESIUM ALLOY IN NACL SOLUTION
Keywords:
Magnesium, Alumina coating, Atmospheric plasma spraying, corrosion resistanceAbstract
Alumina coatings with different thicknesses (160, 240, 320 and 400 µm) were deposited on AZ31B magnesium alloy by plasma spraying. The variation in microstructural characteristics and properties of coatings (porosity and hardness) with various thicknesses were investigated. Powders morphology and the microstructure of as-sprayed coatings were characterized by scanning electron microscopy and optical microscopy. The microhardness was measured using a Vickers' indentor. The corrosion behaviour of plasma-sprayed Al2O3 coatings in 3.5 wt% NaCl solution at a temperature of 25 °C was evaluated by potentiodynamic polarization test. Experimental results indicated that surface roughness showed no obvious dependence on the coating thickness. However, the porosity of Al2O3 coating was increased with increased thickness. The enhanced coating thickness also resulted in decreasing microhardness and reduced corrosion resistance. In this investigation, the Al2O3 coating with thickness of 160 µm possesses the lowest porosity level, the highest hardness and superior corrosion resistance.
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