Microstructure And Properties Of Laser Cladding Ti/TiBCN Composite Coating On 7075 Aluminum Alloy Surface

Aluminum alloys is well-known as a material with a low density,high specific strength,a good plastic toughness,as well as low thermal expansion coefficient and machinability.Thus,aluminum alloys can be used in the automobile,steamships,aerospace and other fields.However,the low corrosion resistance and micro-hardness of aluminum alloys limit their practical application.Therefore,it is of great practical significance to use surface modification technology to improve the corrosion resistance and micro-hardness of aluminum alloy surface.In this paper,7075 aluminum alloy was used as the research object,and the composite coating was prepared on the surface of aluminum alloy by laser cladding to improve its surface properties.The influence of the geometrical characteristics of process parameters laser cladding Ti powder on the 7075 aluminum alloy surface.It is significant that the geometry characteristics of process parameter is laser power,scanning speed and powder feeding rate.The results show that the clad height is controlled by P^1/4S^-4/5F parameter with the correlation coefficient R=0.97.Similarly,the clad width and clad depth are controlled by the P^1/3S^-1/3and P^4/5S^-1/3F^-1/5parameter with the correlation coefficient R=0.95 and 0.96,respectively.The dilution and wetting angle are important geometric characteristic values of good metallurgical combination.The dilution and wetting angle are proportional to P^1/8S^1/5F^-1/2?P^1/2S^-3/4F³/4/4 parameter with the correlation coefficient R=0.95 and R=0.96,respectively.Furthermore,the processing map of the laser cladding of Ti powder on 7075 aluminum alloy substrate is designed by the above empirical relations.The best process parameters are laser power of 1000W,scanning speed of3mm/s,and powder feeding rate of 250mg/s.The influence of TiBCN ceramic powder content on macroscopic morphology and phase composition.When 15wt.%TiBCN powder,the microstructure of the different regions was studied.The results showed that,the clad height of cladding coating is decreases with the increase of TiBCN powder content.The cladding coating presents a relatively flat macroscopic morphology,and the cladding coating has a large number of TiBCN,TiN,Al₃Ti and little of Al,Ti phases with TiBCN content was 15wt.%.The microstructure of coating zone mainly composed of equiaxed grains and white lath-like crystals and that of transition zone mainly consisted of the elongated dendrite crystals and white small particles.The microstructure of the heat affected zone is mainly composed of transverse isoaxial crystals,and the transverse isoaxial crystal rich Al.The influence of TiBCN ceramic powder content on micro-hardness,wear resistance corrosion and electrochemical of the cladding coatings were studied.When TiBCN ceramic powder content was 15 wt.%,the average micro-hardness of the cladding coating is 750HV_0.2,which was about 5 times higher than that of the substrate(¹27HV_0.2).When TiBCN content was 0wt%,the corrosion performance is lower than that of 7075 aluminum alloy.It is good corrosion resistance with TiBCN content was 15 wt.%,and the corrosion potential?Ecorr?reached-1.271 V and the corrosion current density?Icorr?was 3.155e^-005A/cm²,which was one magnitude low than that of the substrate(2.269e^-004A/cm²).Under the same wear condition,the average friction coefficient decreased with the increase of the content TiBCN of cladding coating.When TiBCN content is 15 wt.%,the average friction coefficient is 0.182,the wear loss of 2.4mg,but the substrate of wear loss is 8.2 mg.The surface of 7075aluminum alloy has deep and wide grooves,which is seriously damaged.When TiBCN content is 15wt.%,there are shallow and thin grooves or plastic deformation.