Preparation And Properties Of 7075 Aluminum Alloy By Cold Spraying

Aluminum alloy has been widely concerned for its low density,high strength and corrosion resistance,and has become the preferred material for aerospace industry.However,due to its poor wear resistance,Aluminum alloy parts are easy to fail or scrap due to wear,resulting in great potential safety risks and economic losses.Remanufacturing technology can repair the failed Aluminum alloy parts and reduce the waste of resources to the greatest extent.Although the traditional repair technology represented by thermal spraying technology has been applied to some extent,its extra high-temperature heat source will inevitably have a thermal impact on the repaired parts,bringing negative effects such as thermal deformation,high-temperature oxidation and so on.As a new coating preparation technology,cold spraying has the characteristics of low-temperature solid-state deposition,the deposited layer is dense,and the temperature of raw material is below its melting point in the working process,which is not easy to cause thermal deformation to the substrate,and retains the structure and composition of raw material to the greatest extent,which provides a new possibility for the repair of waste Aluminum alloy parts.However,in the research of the cold spraying technology reported at present,there are still some problems such as low bonding strength and less dense structure in the preparation of Aluminum alloy repair layer,especially the high-strength 7075 repair layer by cold spraying technology.The properties of the prepared Aluminum alloy coating are not ideal,and it can not meet the use requirements of most Aluminum alloy parts.In the manufacturing of aviation industry,5052 Aluminum alloy is often used as the priority material for aircraft mailbox and pipeline,while 6061 and7075 Aluminum alloy are often used as the priority material for turbine disk,gearbox and spacer.Therefore,this project aims at the preparation of 7075Aluminum alloy repair coating by high-performance cold spraying.The 7075Aluminum alloy powder is used as the raw material,and the high-temperature and high-pressure cold spraying technology is adopted,on the basis of different raw material powder morphology?irregular and spherical morphology?,gas temperature?450?,500?,550? and 600??,spraying angle?60°,75°and 90°?and different material characteristics?5052,6061 and7075?were used to investigate the influence of raw material powder characteristics,working gas temperature,deposition angl e and substrate material characteristics on the deposition properties,microstructure and mechanical properties of Cold Sprayed 7075 Aluminum alloy coating.It can provide theoretical support for cold spraying technology to repair key parts of aviation light weight.The results show that the 7075 Aluminum alloy coating with high density?99.9%?,close interface and excellent mechanical properties can be prepared by increasing the main gas pressure to 5MPa only using cheap nitrogen as working gas.At the same spraying temperature,the coating quality of irregular powder is lower than that of spherical powder,and the deposition efficiency is slightly lower.The bonding mechanism between particles and substrate is metallurgical.In the temperature range of 450? to 550?,the main gas temperature has little effect on the microstructure and properties of the coating,and the microhardness has not increased,even slightly decreased.When the spraying temperature increased to 600?,the microstructure of the coating changed abruptly,and the flat macropores of hundreds of microns appeared at the same height of the original dense coating.The porosity of the coating was as high as 4.2%.When the spraying angle increased from 60°to 90°,the comprehensive properties of the coating became worse,the density decreased from 99.78%to 99.48%,the hardness decreased from 137.8 HV_0.1 to 123.7HV_0.1,but the bonding strength decreased from 69.3MPa to 25.3MPa.When the coating is sprayed on 6061 substrate,the particles and the substrate have the same level of coordinated deformation,the bonding strength is higher?more than 56.3MPa?,and the coating performance is better.However,when the particles hit the 5052 and 7075 substrate,the deformation is unbalanced,and the combination of coating and substrate is poor.The results show that the best process parameters of 7075 Aluminum alloy coating is 6061 Aluminum alloy substrate,spherical powder as raw substrate,main gas temperature 500?,spraying angle 60°coating.