Study On Surface Residual Stress Of Preset Tension Laser Cladding

Laser cladding is widely used in surface modification of parts,green remanufacturing and many other fields because of its advantages such as high bonding strength,low dilution rate,small thermal effect on the substrate,and wide range of coating thickness.But the crack sensitivity and crack problem of laser cladding layer,because of its multiple influencing factors and difficult to control,has been a difficult problem for researchers at home and abroad,and also a big obstacle for its engineering application and industrialization.Considering that the residual stress has a great influence on the surface properties of the product,it is also the most fundamental reason for the cracking of the cladding layer.Therefore,in this paper,the residual stress on the surface of Q235 steel cladding layer is controlled by setting the preset stress field,so as to inhibit the generation of laser cladding cracks.The main research contents are as follows.(1)Firstly,the laser power,scanning speed,powder feeding speed and other process parameters were determined,and f3450 iron-based powder was clad on Q235 steel.The pre-set tensile force in parallel cladding direction and vertical cladding direction were set respectively to study.Six groups of pre-set tensile force values of 0n,200 N,400N,600 N,800N and 1000 N were applied,The 20 mm x 5 mm x 10 mm sample was prepared by WEDM.The samples were rough ground with 200 #,400 #,600 #,800 #,1000 #,and the surface oxide was removed by nitric acid.Finally,the required cladding layer was prepared.The surface residual stress of Q235 steel sample was tested by high-speed residual stress tester.Three equidistant test points in a single sample were tested.The surface residual stress values were obtained and the average value was calculated.The influence of different preset tension values on the surface residual stress of the product and the influence of different preset tension directions on the surface residual stress of the product were analyzed,When the tensile force is 600 N,the maximum residual compressive stress is obtained on the surface of the cladding,which has a certain inhibition effect on the cracks.(2)The residual stress analysis model of Q235 steel cladding layer was established by simulation software.The pre-set force field in parallel cladding direction and vertical cladding direction were applied on the simulation model diagram,and the tensile force values were 0n,200 N,400N,600 N,800N and 1000 N.The influence of various pre-set tensile force values on the residual stress of cladding layer surface was solved.Combining the experimental results with the simulation results,the influence of the preset tension on the residual stress of the surface layer of laser cladding products is summarized.It is found that with the increase of the preset tension,the surface residual stress decreases gradually.When the applied tension is600N,the surface has the maximum residual compressive stress,which is basically consistent with the experimental results.(3)Finally,by using microhardness tester,scanning electron microscope and friction and wear tester,the surface hardness,microstructure and wear resistance of the samples under different preset tension values were tested and observed.The results show that with the increase of preset tension value,the hardness value of the cladding layer gradually increases,and the hardness value reaches the maximum when it increases to 600 N.It is found that the martensite on the surface of the cladding layer increases gradually,which affects the hardness of the cladding layer.With the increase of the preset tensile force,the average friction coefficient and wear rate of the sample decrease gradually,and the main wear mode is abrasive wear,which shows the best friction and wear performance at 600 N.