Research On Optimization And Performance Of Laser Cladding Process On Gray Cast Iron Surface

In view of the complex working conditions faced by gray iron castings(engine rolls,machine tool guides,brake discs and industrial valves,etc.),iron castings often fail due to various forms of damage such as wear and corrosion during service.Laser cladding is widely used in the manufacture of high-quality iron castings due to its high energy density,high energy efficiency,low dilution and strong metallurgical bonding.However,in the actual repair and strengthening,the cladding layer is often cracked and fails due to the poor selection of process parameters,the inhomogeneity and incompatibility of thermal physical properties and properties between the powder material and the cast iron matrix,which makes the laser cladding of cast iron.The craft is very difficult.In this thesis,a high-power semiconductor fiber-coupled laser is used to clad the iron-based alloy powder cladding layer on the gray cast iron HT250 flat substrate.Preparation of high-performance cladding layers without cracks and defects on the surface of gray iron castings by two process methods.The first is to manage the cladding layer's dilution rate to limit the melting of the base material,hence minimizing carbon element diffusion in the cladding layer and the likelihood of hard and brittle phases forming in the cladding layer.The response surface approach is used in the test.Dilution rate(DR),cladding width(W),cladding height(H),cladding depth(D),and aspect ratio(W/H)are the key cross-sectional macroscopic geometric properties of the cladding layer.A statistical model is constructed based on the test data between process variables(laser power(LP),scanning speed(SS),and powder feeding speed(PFR))and physical features in the laser cladding process.The model's reliability is tested,and then multi-objective optimization of the laser cladding process' s process variables is performed,in order to regulate the cladding layer's dilution rate,according to realistic engineering.Overlap ratio(OV)is an important process parameter affecting large-area multi-channel cladding,and it is optimized with DR and surface finish(SR)as ideal targets.The second is to repair the gray iron castings by mixing pure nickel powder and iron-based alloy powder in different proportions with a ball mill.Nickel has a strong control effect on carbon distribution in the coating layer and lessens the impact of the bonding zone's hard and brittle structure.To evaluate the metallographic structure,hardness,wear resistance,and corrosion resistance of the cladding layer,a salt spray corrosion chamber,an optical microscope,a digital Vickers hardness tester,a WTM-2E micro friction and wear tester,and a salt spray corrosion chamber were employed.The powder ratio is optimized for the repair of gray iron castings under the same conditions,and the application scope of iron-based alloys in the repair of gray iron castings is expanded while obtaining a high-performance defect-free cladding layer.The experiment results obtained in this study illustrate that the process variables are closely connected to the macroscopic geometric features of the coating layer,that the percentage error of the single-channel cladding layer model is within the allowable range,that the maximum error of the dilution rate is 7.296 percent,and that the optimal single-channel cladding process is 1400 w laser power,6mm/s scanning speed,and 17.2g/min powder feeding rate;under this group of processes.The impact of grain refining and solid solution strengthening lessened as nickel concentration rose,and hardness and wear resistance declined as corrosion resistance increased.The performance of the cladding layer may fulfill the repair requirements of the cylinder liner when 6% pure nickel powder is added to the iron-based alloy powder.