Research On Surface Alloying Of SUJ2 Steel Via Plasma Transferred Arc

Injection molds,as a key process equipment for injection molding,have been widely used in the production of plastic parts for automobiles,medical devices,home appliances,and military industries.As the guiding device of the core pulling device in the injection mold,the inclined guide column has an important influence on the smoothly opening and closing of the injection mold.Since the axial direction of the inclined guide column is not parallel to the opening and closing direction of the injection mold,besides,the thermal stress is generated due to uneven heating of the mold parts during operation,resulting in the inclined guide column enduring a large lateral force,so it is very easy to occur with severe wear.Therefore,in order to improve the wear resistance of the inclined guide column material,quenching or conventional surface hardening methods are generally used.In addition,copper bushings are added outside the inclined guide column,so the assembly is complicated and the cost is high.In order to solve the above problems,a Cu composite coating is synthesized on the surface of SUJ2 steel by plasma transferred arc surface alloying technology.The effects of different process parameters(main arc current,scanning speed and nozzle height)on the alloyed coating were studied.In addition,the influences of the arc current on the wear resistance and wear mechanism of the alloyed layer were investigated at room temperature and high temperature,respectively.For controlling the surface quality of the reinforced materials,the relationship between process parameters and the pool size was established,laying the foundation for later adjustment of process parameters.It is found that after alloying,at low current,there was no alloying layer formed,the microstructure of the heated affected zone mainly consists of cryptocrystalline martensite,retained austenite and spherical carbides without any Cu particles dissolved.With the increase of current,the microstructure of alloying layer consists of plate martensite and residual austenite with many Cu particles dissolved.The width and depth of the pool are steadily decreasing as the scanning speed increased.The nozzle height directly affects the surface quality and molten pool morphology.As the nozzle height increases,the stiffness and stability of the plasma beam decrease,resulting in a decrease in surface quality;at the same time,the width and depth of pool both show a trend of rising first and then decreasing,and in the nozzle height of 5mm,the size of the pool reaches its maximum value.The friction and wear results indicate that micro-hardness of alloyed specimens increased by about 4 times than that of the matrix;the wear rate of the alloyed specimens is much lower than that of the matrix and the remelted specimens,while the wear rate is slightly higher at high temperature.At room temperature,the friction coefficient firstly decreased and then increased with the increase of the main arc current.When the arc current is 90 A,the friction coefficient is the lowest,which is about 29.7% ~ 42.8% lower than that of the matrix;the main wear mechanisms are abrasive wear and slight adhesive wear.At high temperature,the friction coefficient gradually decreases with the increase of the main arc current.Due to the formation of oxide films and Cu films,the main wear mechanisms of the alloyed sample are changed to be dominated by oxidative wear,accompanied with slight abrasive wear,and the friction performance is best when the main arc current was 110 A.In the end,taking the process parameters as input data and the melt pool size as the output data,a BP neural network relationship model with 3-10-2 structure of process parameters and pool size was established,realizing the prediction of the melt pool size under different process conditions.Through verification,the prediction error of this model is within 10%,which has a good prediction ability.