| Chromium plating is one of the most widely used technologies in electroplating industry. Chrome layer has not only beautiful appearance, but also high hardness, good wear resistance and other properties. So it has been widely used in many fields. At the present, the most used chrome plating process is the DC or pulse plating. Due to the restriction of manufacture technology of the pulse power, High-frequency pulse electroplating is general used in the study of pulse electroplating chromium. The frequency is above 100Hz or bi-directional pulse electroplating technology is used. Studies on low frequency pulse plating chromium plating are reported less. In order to improve performance of chrome plating layer and try to find out the effects of low frequency pulse electroplating parameters on preparation technology and coating stability, this experiment is unfolded.In this study, low-frequency pulse plating process was used to study chromium plating, and the pulse frequency was 0~5.0Hz. 30CrMnSiA steel, 1Cr11Ni2W2MoVA and 15-5PH (0Cr15Ni5Cu3Nb) stainless steel are the most commonly used materials for landing gear hydraulic airtight parts, which were selected in this study. On the basis of without changing hexavalent chromium plating chromium solution, the research method which is the combination of five factors five levels orthogonal experiment and single factor experiment is adopted to test and characterize different properties of chromium coating. So a series of meaningful research results can be got.First of all square wave is selected to be as the pulse current waveform by extensive literature analysis and experimental researches. The five research parameters in orthogonal experiment are bath temperature (50 to 60 Celsius degree), plating time (1 to 5 hours), current density (50 to 70 A/dm2), pulse frequency (1.0 to 2.0Hz) and duty cycle (20 to 60 percent). The appearance of chromium coating, thickness, hardness, binding force, micro cracks, porosity, and the average grain size on coating were selected to be the research object. The comprehensive degree of the coating properties of these seven indicators was as the index. By analyzing the data of orthogonal experiment and optimizing the experimental parameters, the final results were got: for 1Cr11Ni2W2MoVA and 30CrMnSiA, the bath temperature is 55 Celsius degree, current density is 70A/dm2, duty cycle is 30 percent, pulse frequency is 3.0Hz and plating time is 3 hours; For 15-5PH, the bath temperature is 55 Celsius degree, current density is 70A/dm2, duty cycle is 40 percent and plating time is 3 hours. At these conditions, the best comprehensive properties can be got on the three types of coating material.In the single factor experiment, the effects of pulse current density, pulse frequency and duty cycle on the properties of chrome plating were studied. By analyzing chrome plating appearance, thickness, hardness, binding force, micro cracks, porosity and the average grain size on coating, the influence order of various factors on the cladding material is concluded. In the experiment of plating chrome plating on the actual workpiece by the best pulse parameters, the bright, uniform, dense chromium plating can be got. Compared with the cladding material by the currently plating process in enterprises, the microstructure of the obtained coatings is more flat, the grain is smaller and the other properties of cladding material can meet production requirements. So the feasibility of this research conclusion can be proved and can provide the scientific basis for the use of low-frequency pulse plating in industrial production.
|
PDF Full Text Request