| High-silicon aluminum alloy has excelient ccharacterisues such as high wear resistance,high conductivity heat transfer ratio,light weight and high strength,and low coefficient of thermal expansion,and there is good compatibility between high silicon aluminum alloy and common aluminum alloy cylinder block.Based on the outsanding wear resistance and light weight and high strength of high silicon aluminum alloy material,by preparing high silicon aluminum coating on the surface of the material can not only improve the wear resistance of the material,but also reduce the weight of the material and realize the light weight.However,considering the current problem that the hardness of high-silicon aluminum coatings is generally not high,this paper proposes to add TiB2 hard particle phase to further enhance the hardness and wear resistance of high-silicon aluminum coatings,and to prepare Al-Si-TiB2 composite coatings to enhance the wear resistance of engines and realize the lightweight of engines.In this paper,the process parameters of Al-Si-TiB2 composite coating prepared by supersonic plasma spraying were optimized by orthogonal test,and four factors and four levels orthogonal tests were established based on four factors affecting the coating:main gas flow rate,secondary gas flow rate,spraying power and spraying distance.Taking the porosity and microhardness of the coating as the main evaluation indexes,the optimal spraying process parameters of Al-Si-TiB2 composite coating were determined.The microstructure and mechanical properties of the composite coating were characterized.At the same time,the friction and wear experiment of the high-silicon aluminum coating was carried out by simulating the actual working condition of the engine,and the wear mechanism was analyzed.According to the actual service conditions of the engine,the heat treatment experiment of the high-silicon aluminum coating was carried out to explore the influence of high temperature on the wear resistance and wear mechanism of the coating and its rule.The specific research contents are as follows:(1)Through four-factor and four-level orthogonal tests,taking porosity and microhardness of coating as evaluation indexes,using range method and comprehensive score,the main and secondary factors affecting microhardness and microhardness of coating were obtained.The optimal spraying parameters of the coating were obtained by comprehensive scoring index.Then by changing the most important factors affecting the evaluation index,six groups of validation tests including better spraying parameters were developed.Finally,the best spraying parameters were determined by comparing the highest average hardness with the lowest porosity.(2)The Al-Si-TiB2 composite powder obtained by ball-milling and mixing was irregular in shape,and after the composite coating was prepared by supersonic plasma spraying,the average hardness of the coating reached 348.8 ± 37.6 HV0.2,which is a significant increase compared with that of the Al-Si coating.The main reason for the hardness enhancement is the addition of TiB2 hard particle phase,which leads to a significant increase in the hardness of the coating,and the average bond strength of the composite coating is 37.2 MPa.(3)The friction and wear tests of the composite coating were carried out.UMT-3 friction and wear tester are used.The average friction coefficient of the composite coating is 0.09,the total wear amount is 0.31×10-3 mm3,the width of the abrasion marks is 1.5mm,and the depth of the abrasion marks is 1.75μm.The wear amount was reduced by 57.5%compared with that of Al-Si coating.The wear mechanism of the coating under the oil lubrication condition is mainly the two-body abrasive wear with furrow cutting,extrusion spalling and abrasive wear.(4)In order to simulate the actual working condition of the engine,heat treatment experiments were conducted for the composite coating.Through the DSC analysis of the coating,and combined with the actual operating temperature range of the engine 100-300℃,the heat treatment scheme of the composite coating is selected as follows:150℃×48h,150℃×96h,200℃×48h,200℃×96h,250℃×48h,250℃×96h.It is found that the microhardness of the composite coating after heat treatment decreased gradually with the increase of the heat treatment time gradually decreases.In addition,with the increase of heat treatment temperature,the wear amount of composite coating also increases and the wear mechanism should be shown as abrasive wear,which is transformed into abrasive wear+adhesive wear after heat treatment at 250℃. |
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