Study On The Bonding Properties Of Plasma Sprayed Coatings And Aging Aluminum Alloys

Using plasma spraying technology to spray a hard coating on aluminum alloy substrate can effectively improve its wear resistance and service life.However,the low bonding strength between the coating and the substrate is a critical problem restricting its application of plasma spraying on aluminum alloy substrate.In the present paper,the bonding layers of NiCrAlY,Ni/Al and working coating of Ni60 A were deposited onto 6061 aluminium alloy substrate to improve the bonding strength between the coating and the substrate.The bonding strength of different spray materials and substrates were compared and the plasma spray parameters of NiCrAlY bonding layer and Ni60 A working coating were optimized.The influence of coating thickness on bonding strength was studied for coatings produced with optimized spray process.The effect of solid solution-aging of the substrate alloy prior to or after plasma spray on the bond performance of the coating and the surface properties of the substrate were investigated.On the other hand,NiCrAlY bonding layer and Ni60 A working coating prepared on the solution-aged substrate were heated and the effects of heating at different temperatures on the bonding strength of the coating was inspected.The morphology of particle deposition,microstructure,phase components and interface between coating and the substrate were analyzed.1.The bonding strength between the NiCrAlY layer and substrate is 32.5 MPa and the adhesion is 106.8N,better than those of the Ni/Al bond coating which are only 17.5MPa and 23.4 N.2.At spray power of 30 kW NiCrAlY layer shows the best bonding performance with the substrate.The bonding strength of the NiCrAlY coating reaches 34.8 MPa and the adhesion is 108.2 N.The working coating in of Ni60 A is the most compact and has the best bonding performance with the substrate when the spray power is 35 kW.The porosity and the bond strength of the Ni60 A coating were measured to be 3.2% and 30.4 MPa respectively.An increase in porosity,a decrease in bonding strength and microhardness,of the coatings were observed with increasing coating thickness.3.Solid solution-aging treatment of the alloy substrate after plasma spray coating reduces the bonding strength between the coating and the substrate.While plasma spray shows little effect on the property of the substrate and the bonding strength between the coating and the substrate.4.For the Ni60 A coating,the porosity is decreased and the bonding strength increased significantly,if heating-treated at 200 °C for 6 hours.The microhardness of the heated coating increased by 16.12% and the bonding strength increased by14.5% compared with the unheated coating.However,excessive heating temperature leads to aggravate oxidationof coating-substrate interface and deteriorate severely the bonding strength.