Research On Process Of Ni60 Alloy Coating Cladded By Laser On Mold Copper Plate

Because of its good thermal conductivity,copper alloys are often used to make continuous casting mold copper plates.The development of high-speed continuous casting puts forward higher requirements on the surface performance of the mold.When used in harsh environments,the mold copper plates are prone to surface wear.,High temperature oxidation and thermal cracking and failure.The damage of the crystallizer seriously restricts the production efficiency of the enterprise.For this reason,it is of great significance to prepare a crystallizer working mask with high wear resistance.Compared with the traditional surface modification technology,the coating prepared by the laser cladding technology has the advantages of high bonding strength,fewer defects,and the coating materials can be freely proportioned according to the requirements of use.Because of the very high reflectivity of copper-based materials to the laser and high thermal conductivity of its own,this project adopts a pre-heating method.The coaxial powder feeding laser cladding technology is used to strengthen the surface of the mold copper plate,and successfully prepared A single pass of Ni60 cladding layer,and found the best comprehensive quality process parameters.The cladding process was simulated and analyzed by ABAQUS,the heat transfer and internal temperature field related characteristics of the coaxial powder feeding laser cladding process were explored,and the defects in the experiment were analyzed with the help of temperature field.The internal structure and phase distribution were observed and judged by scanning electron microscopy and X-ray diffractometer.The solidification process of the structure was analyzed by the temperature field of numerical simulation,and the hardness and friction and wear experiments of the cladding layer were done.The hardness and friction and wear properties are analyzed according to the structure and the equivalent.The main results of this project on the above work are as follows:(1)For the chromium-zirconium-copper substrate coaxial powder feeding laser cladding Ni60 coating,the optimal process is: the laser power is 1700 W,the heat source moving speed is 3mm/s,the preheating temperature for the substrate is 500℃,and the powder is fed.The rate is 6g/min,and the spot diameter is a fixed value of 2.4mm.Considering these factors for the quality of coating preparation,when the laser power is 1700～2000W,the heat source moving speed is 3～4mm/s,the preheating temperature is 500℃,and the powder feeding rate is6～12g/min,the melt prepared The cladding has high bonding quality with fewer defects and suitable morphology.(2)According to the ABAQUS simulation of the cladding process: the highest temperature during the cladding process is located at the center of the spot on the surface of the cladding layer,and in three spatial directions,the farther away from the center of the spot,the lower the temperature.Among them,the changes along the longitudinal direction are the most dramatic.The maximum temperature during the cladding process is constantly increasing.For the nodes on the cladding layer,the temperature rise process is basically completed in an instant,and the descending process is also very short but significantly longer than the temperature rise process.Among them,the higher the laser power,the higher the overall temperature of the temperature field.The size of the laser spot and the moving speed of the heat source are negatively related to the temperature of the temperature field.The pre-heating temperature has no obvious effect on the maximum temperature of the cladding layer,but It has an obvious inhibitory effect on the temperature drop rate.(3)Regarding the defects in the experiment process: the fat of the cladding layer is mainly caused by the excessively small heat source moving speed and the accumulated droplets;the residue on both sides of the cladding layer is due to the linear energy density during the cladding process As a result,the molten pool is relatively small and cannot be completely combined with the droplets;the contamination of the composition of the matrix to the composition of the cladding layer is inevitable in the laser cladding process.For this topic,the dilution rate of the cladding layer is relatively low and uniform.Below 15%,it is acceptable;the existence of pores is mainly caused by insufficient drying of the powder and the excessively large cladding layer due to the very short solidification time of the top cladding layer,which makes the pores too late to overflow before the top of the cladding layer solidifies;As the maximum temperature of the cladding layer continues to increase,the size of the cladding layer is also increasing.This situation can be solved by gradually increasing the cladding speed and reducing the laser power.(4)The microstructure of the cladding layer from the bonding zone to the top of the cladding layer changes from planar crystals to dendrites to cellular crystals.According to the analysis of the temperature field on the solidification process of the structure,when the control shape control factor K value is low At 190×106℃·s,the structure is cellular crystal form,and when it is higher than 190×106℃·s,it is columnar dendritic form.Among them,the microhardness value of the cladding layer is about 800 HV on average,which is about 5 times higher than the 160 HV of the substrate.Under the same friction and wear test conditions of the prepared Ni60 cladding layer and the substrate,the weight loss of the coating is only 13.33%of that of the substrate.The wear resistance has been significantly improved.