The Effect Of Electromagnetic Stirring And Rare Earth La Addition On Microstructure And Properties Of Al-Sn Alloy

Al-Sn alloys have excellent bearing properties and are lead-free and environmentally friendly,making them attractive as bearing materials.With the advancement of industrial technology,the working environment of bearings is becoming more and more complex,and it needs to work for a long time under special conditions such as high temperature,high load and strong corrosion,which puts forward higher requirements for the performance of bearing materials.In this paper,Al-Sn alloys were prepared by electromagnetic stirring(EMS)technology and the addition of rare earth La.The friction and wear test,electrochemical test and immersion corrosion experiments were carried out,combined with scanning electron microscope,3D surface profiler and X-ray photoelectron spectroscopy to study the effects of different stirring parameters and rare earth La content on the microstructure,tribological properties and corrosion resistance of Al-Sn alloys.The main results are as follows:(1)The Al-Sn alloy as-cast microstructure is dendrite.By controlling the magnitude of EMS current and frequency,the adhesion between grains is significantly improved,the grain size is reduced,and the morphology is more regular.When the stirring parameters are 60 A,30Hz,the average grain size decreased from 49.68μm to 21.72μm,decrease by 56.3%.With the addition of rare earth La,microscopic defects such as surface cracks and segregation of AlSn alloys are reduced.When the rare earth content is 0.34 wt.%,the Sn phase is uniformly distributed in the shape of short strips or ellipsoids,and the grains are refined.(2)The tribological properties of Al-Sn alloy were improved with the application of EMS,the fluctuation of the friction coefficient curve became smaller,and the peeling of the worn surface was reduced.The wear surface forms a smooth continuous oxide film,which plays a self-lubricating role.When the stirring parameter is 60 A,30Hz,the average friction coefficient and wear volume are the smallest,which are 0.312 and 0.1168mm~3,which are respectively 35.8%and 81.3% lower than those of the samples without EMS.The existence of rare earth hard spots provides the required strength of the alloy,and the wear resistance of the alloy is optimized to a certain extent.However,with the increase of La content,there are more hard particles that peel off the surface during the friction process,resulting in abrasive wear and weakening the tribology performance.(3)After applying EMS,the refined microstructure makes the chemical composition of the Al-Sn alloy more uniform,reduces local electrochemical differences,and reduces corrosion susceptibility.When immersed for 720 h,there are more corrosion product films composed of fine particles on the surface,the pores are reduced,the density is increased,and more Sn O2 is generated,which is beneficial to improve the corrosion resistance of the alloy.The corrosion performance of Al-Sn alloy increases first and then decreases with the increase of La content.Rare earth oxide La2O3 was detected on the surface of the La alloy,which was closely combined with the corrosion product film and improved the density of the corrosion product film.