Study On HVAF WC Coating Sprayed At Aluminum Substrate

Aluminum alloy has been widely used in aerospace,aeronautic,car and ship industry due to its high specific strength,good thermal conductivity,moldability,low price and etc.Especially high strength Aluminum alloy there is wide application in aerospace,aeronautic,vehicle and ship etc industry as one of the main structural materials.However,high strength Aluminum alloy owns low hardness and bad wear resistance,therefore it is significant to enhance its hardness and abradability to extend its application field and make launch vehicles light weight via surface treatment.In this paper,High-Velocity-Air-Fuel(HVAF)WC-14Co and WC-10Co4Cr coatings on 7075 aluminum alloy substrate were prepared.The microscopic structure and chemical composition of both coatings were investigated by SEM,XRD and EDS respectively.Under tensile state,stress distribution at the interface between coupled part and glue was analyzed by finite element analysis.The result shows that large stress concentration at the interface between coupled part and glue was occurred as a result of low elastic modulus of coupled part,resulting in the failure of glue at low stress level. The bonding strength between the 7075 aluminum alloy substrate and WC coating was higher than 50MPa due to the glue failure.The bonding mechanism of HVAF WC coating was mainly governed by mechanical bond through splat analysis;also the metallurgical bond seemed to take effect.Wear behaviors of WC coatings demonstrated that adhesive in WC coatings was firstly worn and led to the outstanding of WC on the surface;then the outstanding WC was subsequently fractured and stripped from the coating,finally WC abrasives were observed due the stripping of surrounding WC at the large stress.The pull-out of WC particles degraded the wear resistance of WC coatings,and accelerated the wear of binder and newly exposed WC particles.The wear mechanism for HVAF WC coating against GCr15 steel was dominated by abrasive wear.The results of neutral salt fog experiment indicated that the corrosion resistance of the substrate and the coated 7075 Aluminum was ranked as:WC-10Co4Cr coating+ sealing treatment＞WC-10Co4Cr coating＞WC-14Co coating+sealing treatment＞WC-14Co coating＞7075 Aluminum substrate.Sealing treatment was beneficial to corrosion resistance.The mechanism was governed by the preferential corrosion of adhesive phase and the pervasion of corrosion medium into interface.Once corrosion medium reached interface,the preferential corrosion of substrate was occurred due to low corrosion potential.