Research On Remanufacturing Repairing Of Cylinder Liner By Steady-State Magnetic Field Assisted Laser Cladding

With the vigorous development of the national economy and the growing equipment manufacturing industry,the working conditions of equipment parts required by all walks of life are becoming more and more complex.Many components fail before their service life,resulting in a huge waste of resources.Marine diesel engine is an important power plant on the ship,and cylinder liner is an important part of it.However,the working environment of cylinder liner is very bad.Reciprocating friction and electrochemical corrosion caused by coolant affect the service life of cylinder liner,resulting in early scrapping of cylinder liner and waste of resources.Through laser cladding technology,the repair and reuse of cylinder liner can be realized and the use efficiency can be improved.In order to further improve the repair quality,this paper investigates and analyzes the application of magnetic field assisted laser cladding technology at home and abroad.The variation characteristics of temperature field and velocity field of molten pool under steady-state magnetic field were simulated by COMSOL Multiphysics,and the steady-state magnetic field assisted laser cladding experiment was carried out at the same time.The microstructure and properties of the cladding layer were analyzed by means of characterization.The results show that :(1)The influence mechanism of the steady-state magnetic field on the molten pool mainly includes two aspects : one is the electromagnetic braking effect of the steady-state magnetic field on the molten pool,and the other is the thermoelectric magnetic fluid effect of the steady-state magnetic field.The electromagnetic braking effect will weaken the flow velocity of the fluid,thereby inhibiting the formation of equiaxed crystals and promoting the growth of columnar crystals.The thermoelectric electromagnetic force acting on the dendrites by the thermoelectric magnetic fluid effect will play a role in grain refinement.The velocity field and temperature field of the molten pool were simulated by COMSOL Multiphysics.The results show that the steady-state magnetic field could inhibit the convection inside the molten pool,and the change of molten pool temperature is small.(2)According the perspective of the morphology and structure of the molten pool,as the steady-state magnetic field strength increases,the molten pool tends to be flat and the dilution rate decreased.When the horizontal magnetic field was applied,the height and width of the molten pool were larger,and the penetration depth and dilution rate were lower.With the increase of the steady magnetic field strength,there was a phenomenon that the dendritic structure transforms into equiaxed crystal structure in the middle and top of the cladding layer.At the bottom,a large range of directional and thicker columnar dendrites appeared,and the growth direction of the dendrites at the bottom tended to turn to the direction of the magnetic field.The steady-state magnetic field did not change the phase composition in the cladding layer.As the magnetic field strength increased,the matrix phase content increased,the Laves phase content decreased,the grain size decreased,and the crystal structure was stabilized.(3)According the experimental data of mechanical properties,the microhardness of the cladding layer was much higher than that of the matrix,and the hardness distribution value increased with the increase of magnetic field strength,and the wear resistance and corrosion resistance were improved.When the steady-state magnetic field was vertically downward,the hardness of each region of the cladding layer was the highest,the wear resistance was better,and the corrosion resistance of the cladding layer was lower than that in the horizontal direction.