Research On Preparation And Properties Of Plasma Sprayed Fe-based Coatings On Aluminum Alloy Surface

Energy saving and emission reduction are huge challenges for automobile manufacturing industry.The lightweight and performance improvement of engine is one of the important ways to solve this problem.Although the aluminum alloy engine cylinder meets the requirement of lightweight,their poor wear resistance is prone to cause the failure of the inner surface of the cylinder.Compared with the traditional embedded cast iron cylinder liner,the preparation of the coating on the inner wall of the cylinder can improve the wear resistance and reduce the overall quality of the cylinder.In this study,Fe-based coatings were prepared by supersonic plasma spraying technology on the aluminum alloy substrate,including gray cast iron,high-chromium steel and Fe-based self-melting alloy materials,and the performance of the coatings was evaluated by combining the microstructure,phase composition,hardness,bonding strength and wear performance of the coatings.In order to further improve the wear performance of the best Fe-based coating material selected by the experiment results,the effect of the addition of Mo S₂solid lubricant on the microstructure and related properties of Fe-based self-lubricating composite coating was systematically studied.The results show that the oxide content of gray cast iron coating is much higher than that of high chromium steel and Fe-based self-melting alloy coating.Before and after spraying,the high-chromium steel coating did not undergo phase transformation,while the transition of?-(Fe,Ni)phase into?-(Fe,Cr)phase was confirmed in the Fe-based self-fluxing coatings.The microhardness of gray cast iron coating,high chromium steel coating and Fe-based self-melting alloy coating were 313±12HV_0.1,394±27HV_0.1and 428±17HV_0.1,respectively,which were significantly higher than that of aluminum alloy substrate(29±4HV_0.1).The bonding strength of high chromium steel and Fe-based self-melting alloy coating is higher than that of gray cast iron coating,which is mainly attributed to the lower oxide content in the coating and Cr and Ni alloy elements effectively promote the mutual diffusion of Fe and Al between coating and substrate interface.According to the results of friction coefficient and wear volume loss,gray cast iron coating,high chromium steel and Fe-based self-melting alloy coating showed good wear resistance compared with aluminum alloy substrate,especially the wear volume loss of the high chromium steel coating is reduced by 98.8%compared to the aluminum alloy substrate.Therefore,compared with gray iron and self-melting alloy coatings,high chromium Fe-based coatings have both good bonding strength and wear performance.Fe-based self-lubricating composite coatings with different contents of Mo S₂were successfully prepared,and the Mo S₂in the coatings was not completely decomposed.With the increase of Mo S₂content,the microhardness and interfacial bonding strength of the coating decreased gradually.When the Mo S₂content increased from 0wt.%to15wt.%,the friction coefficient and wear mass loss of the coating presented a trend of decreasing first and then increasing.When the Mo S₂content added in the high chromium Fe-based coating material is 5wt.%,the Mo S₂lubricating phase can be well combined with the Fe-based material and has a good self-lubricating effect,the friction and wear performance of the coating is improved,that is,the lowest friction coefficient(0.5)and wear mass loss(0.0704mg).The wear mechanism of the Fe-based composite coating with 0wt.%Mo S₂was oxidative wear,and the wear mechanism of the Fe-based composite coating with 5wt.%,10wt.%and 15wt.%Mo S₂was coexistent of oxidative wear,abrasive wear and fatigue wear.