Process Study Of Chemical Liquid Assisted Laser Polishing Of Ti6Al4V

Ti6Al4V,also known as TC4,is an α+β titanium alloy with high strength,low density,excellent fracture toughness,corrosion resistance,heat resistance,and biocompatibility;it is widely used in various fields.Usually,3D printing technology is used for processing and manufacturing Ti6Al4 V,but there will be a step effect,resulting in a high surface roughness of Ti6Al4 V,which has a great negative impact on the biocompatibility and corrosion resistance of Ti6Al4 V.Therefore,polishing processing of Ti6Al4 V is necessary.Laser polishing,as an advanced polishing technology,can effectively reduce the surface roughness generated in modern manufacturing processes and thus improve the processing quality.However,laser polishing of metals produces heat-affected zones and microcracks on the workpiece surface,and these defects still need to be addressed by exploring new treatment methods.In this regard,this paper will explore the mechanism of the action of two kinds of laser polishing Ti6Al4 V through the comparison experiment of nanosecond laser and picosecond laser,and newly propose a new process of chemical liquid assisted laser polishing,which has the advantage of removing the heat-affected defects of laser polishing cleanly without damaging the workpiece,and can reduce the roughness of Ti6Al4 V surface and improve the surface properties The process has an important theoretical significance and practical value for promoting the comprehensive development of Ti6Al4 V polishing technology in China.Through the comparison experiment of Ti6Al4 V polishing by nanosecond laser and picosecond laser,the optimal process parameters for Ti6Al4 V surface polishing by nanosecond laser were determined as follows: scanning speed 100 mm/s,scanning times 10,laser power 12 W,repetition frequency 200 k Hz,and surface roughness reduction rate of 70 %;the optimal process parameters for Ti6Al4 V surface polishing by picosecond laser were The optimal process parameters for Ti6Al4 V surface polishing by picosecond laser are: scanning speed 400 mm/s,scanning times 4,laser power 9 W,repetition frequency 600 k Hz,and the surface roughness reduction rate is only 39 %.The average surface hardness of Ti6Al4 V after nanosecond laser polishing was increased by nearly 60 HV or 17.6 % compared with that before polishing for both lasers at the optimal process parameters;the average surface hardness of Ti6Al4 V after picosecond laser polishing was almost the same as that before polishing.The basic reason is that the polishing mechanism of the two is different,the thermal effect of nanosecond laser is stronger and that of picosecond laser is relatively weaker,and for the metal material like Ti6Al4 V,the nanosecond laser which can produce stronger thermal effect is obviously more suitable for polishing processing than the picosecond laser.The strong thermal effect of nanosecond laser polishing makes the temperature gradient of Ti6Al4 V surface too large,resulting in a series of heat-affected defects on the polished surface,the most obvious of which is microcracking.A chemical liquid assisted nanosecond laser polishing of Ti6Al4 V is proposed as a process to eliminate microcracks.A 5 mol/L sulfuric acid solution was chosen as the chemical solution medium,and the thickness of the chemical solution film was controlled at 2 mm～2.5 mm in the polishing experiments.The laser process parameters and surface roughness were modeled using Design-Expert software,and the analysis based on the proposed model showed that the laser power had the most significant effect on the surface roughness,followed by the scanning speed and the number of scans,and the repetition frequency had the least effect on the surface roughness.The optimal process parameters for chemical liquid assisted laser polishing of Ti6Al4 V are: scanning speed of 500 mm/s,laser power of 10 W,number of scans of 12,and laser frequency of200 k Hz.polishing experiments using the optimal parameters,the actual surface roughness after polishing is detected to be 0.507 μm,and the actual reduction rate is65%,which is in accordance with the established model.The scratch grooves on the Ti6Al4 V surface were significantly removed after chemical liquid assisted laser polishing,and no significant microcracking phenomenon was observed.The average surface hardness after polishing increased from 315.3 HV to 328.7 HV,an increase of4.07%.The results of this paper have a certain reference value for laser polishing of Ti6Al4 V,and are of great significance for subsequent experiments to eliminate heat-affected defects,reduce microcracks,optimize the polishing process parameters and improve the polishing quality.