Tribological properties and microstructure of plasma sprayed high silicon aluminium alloy coatings

Plasma spraying was carried out on aluminium alloy substrates using high silicon aluminium alloy powders (Al-40Si-Cu-Mg) to improve the wear resistance of the aluminium alloy. The coating exhibits superior more wear resistant to cast A390, and a low friction coefficient ranging from 0.2 to 0.25. The sprayed coating is much higher hardness of HV260 compared with that of cast A390, be cause of its quenched microstructure with sub-micron size silicon particles. The coating hardness does not decrease as annealing temperature up to 573 K, above 573 K it decreases rapidly. This drop in coating hardness is related to the coarsening of silicon particles and thus expanded interparticle distance. The wear resistance of coatings after annealing is inferior to that of sprayed coating. This is attributed to decrease in hardness value and coarsening of the microstructure. After annealing, the friction coefficient of the coatings shows a remarkable increase with increasing sliding distance. Since the plasma sprayed coating is in a non-equilibrium state, it maintains low friction coefficient even with a long sliding distance. Therefore, improvement in tribological properties is considered here to be due to change in wear mechanism brought by the formation of film-like layer, which prevents coating surface from adhering to iron.