| High-silicon aluminum alloy has excellent properties such as light weight,high strength,high thermal conductivity,excellent wear resistance and low thermal expansion coefficient.It has good compatibility with aluminum alloy cylinders and pistons.Refer to the literature to prepare high-silicon aluminum alloy cylinder liners by spray deposition technology.However,due to its very complicated process and low production efficiency,the preparation cost is relatively high.Based on the development of high-silicon aluminum alloy as the surface wear-resistant layer,this paper uses the internal diameter-supersonic plasma spraying high-silicon aluminum coating to achieve wear-resistant strengthening on the inner wall of the cylinder to replace the role of the cylinder liner and realize the lightweight of the engine.This article first optimizes the process parameters of the internal diameter-supersonic plasma spraying,and then explores that the total gas flow,hydrogen content,current,voltage and spraying distance have relevance to the temperature as well as velocity of the flying particles in the plasma jet.At the same time,the influence of the temperature and speed of the flying particles on the quality of the coating was revealed,and the optimal process parameters for the preparation of the inner hole high silicon aluminum coating were determined.With the help of modern analysis methods,the microstructure of the inner hole coating is characterized and its mechanical properties are tested.Simultaneously,the wear resistance of the inner hole coating is tested by simulating actual working conditions,and its wear mechanism is analyzed.The influence of temperature on the wear resistance and wear mechanism of the coating under actual service conditions was explored.The main conclusions are as follows:(1)With a fixed power of 32kW,the increase in the total gas flow rate increases the particle temperature and velocity by approximately 12.2%and 46.9%,respectively.The increase in hydrogen content has basically no effect on the particle temperature,but will reduce the particle velocity by 12.5%.When the voltage is constant and the current increases,the particle velocity increases by 12.3%,while the temperature only increases by 4.3%.As the spraying distance increases within the test range,the particle temperature first increases and then decreases,and the particle velocity decreases monotonously.If the surface temperature of flying particles increases during deposition,the coating will melt more uniformly and the average microhardness will increase by 22.9%.If the speed of flying particles is increased during deposition,the porosity is reduced by 84.2%and the pore size is also greatly reduced.The optimal process parameters:total air flow 115L/min,hydrogen content 7.5%,voltage 86V,current 430A,spraying distance 90mm.(2)The ?-Si phase in the sprayed powder has a large size(above 3?m)and has an irregular shape.After the coating is prepared by internal diameter-supersonic plasma spraying,the size of the ?-Si phase is significantly refined(nano-level),and the shape is mostly spherical small particles.The average hardness of the inner hole coating is 267.09±14.85HV0.2,and its relatively high hardness is mainly due to the effects of fine-grained strengthening and solid solution strengthening.The average bonding strength of the inner hole coating is 44.1MPa.The tensile fracture site is on the side of the substrate where the substrate and the coating are joined.(3)The total wear of the inner hole coating is 2.77×10-3mm3,the width of the wear scar is 654.3?m,the depth of the wear scar is 8.95?m,and the average friction coefficient is 0.20.The wear mechanism of the coating under oil lubrication conditions is mainly the furrow cutting and extruding peeling in the two-body abrasive wear,the three-body abrasive wear and a small amount of oxidative wear.The main material loss mechanism of the inner hole coating is the pressing of the grinding ball and cutting the worn surface,the shedding of the Si phase,and the exfoliated Si phase and oxide cutting the worn surface.(4)After the heat treatment at 255?,the silicon phase particles in the coating begin to aggregate and become massive,and the activation energy of the coarsening of the silicon phase in the coating is much smaller than the self-diffusion activation energy of silicon atoms,indicating that as the heat treatment temperature rises,the way silicon atoms diffuse From the interfacial diffusion dominated to the bulk diffusion dominated.After heat treatment,the microhardness of the coating decreases first and then stabilizes with the extension of the heat treatment time.This is formed by the joint action of the solid solution strengthening and the fine-grain strengthening failure and the precipitation strengthening.The amount of coating wear increases with the increase of heat treatment temperature.The wear mechanism is originally characterized by abrasive wear+a small amount of oxidative wear.After heat treatment at 255?,it transforms into abrasive wear+adhesive wear+a small amount of oxidative wear. |
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