Study On Performance Of WC Coated 7A09 Aluminum Alloy By Thermal Deformation

7A09 high strength aluminum alloy with strong plastic deformation capacity,however its low wear resistance and corrosion resistance greatly limit its application range.High-velocity air-fuel spraying is an effective metal surface reinforcement technology and WC-10Co4Cr is a cermet composite coating material?hard alloy?with excellent corrosion resistance and friction resistance.Through the HVAF method,preparing the WC-10Co4Cr coating on the surface of7A09 aluminum alloy can enhance the wear resistance and corrosion resistance of 7A09aluminum alloy,which is significant.7A09 aluminum alloy is mainly used in harsh environments such as military and aerospace,the bonding strength of its coating should be high.The coating prepared by HVAF cannot meet the requirements.So exploring the method of reinforcing the bond strength between WC-10Co4Cr coating and 7A09 aluminum alloy,will greatly improve the life of the 7A09 aluminum alloy product and expand its application range.To prepare the WC-10Co4Cr coating with better performance on the surface of 7A09aluminum alloy,the orthogonal method was used to optimize process parameters.In the coating process,the WC-10Co4Cr powder with a particle size of 15-38?m is coated through the supersonic thermal spray equipment of Kermetico and the spray gun of CK05.The process parameters for obtaining the optimum coating performance are:air pressure is 89MPa;propane pressure is 91 MPa;combustion chamber pressure is 80.4 MPa;powder feeder speed is 6 rpm,traverse speed is1500 mm/s,spray distance is 180 mm,step distance is 2 mm.The calibration standard for the Bonding strength is established,which is the scratch method combined with EDS testing the main elements of the matrix.Due to the high bonding strength of the WC coating prepared by HVAF,the bonding strength of the coating cannot be determined according to the ASTM C 633?Stretching method is limited by bond strength?.Since the defects are not obvious in the scratches,the failure phase of the WC-10Co4Cr coating cannot be judged by the scratching method specified in GB/T30707.Through the principle of detecting the bond strength of the coating by the scratch method,the Al content in the scratched micro-area is detected by EDS and the bonding strength is calibrated.The bond strength of the coating prepared in this study was tested.The results showed that the minimum critical load is 160 N.For the first time,the method of thermal compression deformation was used to enhance the performance of the coating.The hot compression deformation was carried out for the7A09 aluminum alloy prepared with the WC-10Co4Cr coating.The conditions is the different temperatures?360?,390?,420?,450??,different deformation amounts?4%?0.2 mm?8%?0.4mm?,12%?0.6mm?,16%?0.8mm?,20%?1mm??and compression rates of 0.01s-1.The effect of hot compression deformation on the surface hardness of coating:the temperature rise causes the WC coating to form oxide phases with higher hardness such as CoWO₄,Cr₂O₅ and C₆WO₆.The increase in particle density and the reduction in porosity can improve the microhardness under the influence of pressure.At the deformation temperature of450?and the deformation of 16%,the microhardness of the coating is increased by 15%compared to the initial microhardness.The effect of hot compression deformation on bond strength:the transition layer with W and Al as main components in the mixed phase of the interfacial layer gradually disappears with the diffusion of Al.At the deformation temperature of 450°C and the deformation of 4%,the atom diffusion of the interface layer makes the content of each phase component basically keep balance.The material begins to flow in a steady state and the compressive stress load is small.Without affecting the performance of the coating,the bonding state of the interface layer is strengthened and the bond strength increased by 6.3%.In the process of increasing the deformation,the main factor affecting the gap between the coating and the matrix and increasing the contact area is the rheological degree of the interface layer matrix.At the deformation of 8%,the strengthening effect of the bonding strength is obvious,and the critical load for characterizing the bonding strength reaches 188N,which is 17.5%higher than the initial critical load;As the deformation increases,the rheological degree of the interface layer matrix material increases,destroying the original bonding state of the coating layer and the matrix,and the bonding strength begins to decrease.In summary,the performance of WC-10Co4Cr coating prepared on the surface of 7A09aluminum alloy by HVAF technology meets the requirements of the thermal spray and powder quality;The calibration method of high bond strength coating strength proposed in the work is practical in applications;The thermal compression deformation method has a significant strengthening effect on the microhardness and bonding strength of the coating.