Mechanism And Mechanical Properties Of The Coating On Aluminum Produced By Friction Stir Processing

The aluminum alloy surface thermal spray coating for coating internal porous structure is not uniform, dense defects leads to the poor mechanical performance, and between the coating and the substrate was not well combined with problem, this work using friction stir processing technology of thermal spraying coating was modified, to expect to help provide reference for the related research work.Using friction stir processing technology, processing the reaction spraying preparation of Al2O3-TiB2 multiphase coating on aluminum alloy. The mechanism and the effects of friction stir processing were studied; wear resistance and bonding strength of the coating were studied. This project has obtained the following important research results:(1) After the friction stir processing,the gap between the original laminated and porous particles almost disappeared with the effect of strong pressure and high temperature, the gap between coating and substrate have narrowed. The microstructure became compact and dense after FSPed. The coating organization has experienced the following stages: thinning compaction, streamline organization, dynamic recrystallization, and dense fine grain structure. Fusion utilizes between the coating and the substrate, the gap between coating and substrate disappear. The alloy elements in the substrate diffuse to the coating.(2) After the friction stir processing, the coating micro hardness increase from 62 HV to 269 HV. The hardness of compacted tissue reached 85 HV, and the hardness of streamline organization reached 151 HV. The binding strength increases from 5.2MPa to 48.6MPa. After friction stir processing, the wear resistance of the coating has been greatly improved, the average wear rate for 0.141g/h before the FSP, the average wear rate is only 0.00256g/h after the FSP.(3) Friction stir processing technology is a kind of hot machining deformation technology, which has a good comprehensive processing ability. By deformation induced split mechanism, multiple slip bands form in the original grain first, then the dislocations increase and aggregate to form small angle grain boundaries, and gradually transform into large angle grain boundaries, eventually the grain will split into many more fine grains Stirring friction processing of thermal mechanical deformation of the high temperature and high pressure dynamic recrystallization driving force, high strain rates of the fine grains are preserved, final coating microstructure evolution, dynamic recrystallization grain fine grains instead of the original structure.