Study On Coated Electrodes In Resistance Spot Welding Of Galvanized Steel Sheet

In this paper, deposit Ni / metal-ceramic coating on Cu-Cr-Zr electrodes by electric-spark deposition technique. Studied on using orthogonal test method deposition process on the deposition efficiency and coating quality and the impact, and optimize the process parameters. Use optimized coating fabricated by resistance spot welding galvanized steel sheet electrode. According to the shear strength of resistance spot welding joints standard assessment of coated electrodes and the non-coated electrode life; using scanning electron microscopy, energy dispersive spectroscopy and hardness testing by means of analysis of coated electrodes and the non-coated electrode before welding, 300 solder joint failure during and after the appearance, structure and composition. On this basis, discusses the failure mechanism of galvanized steel welding electrodes, and propose further measures to improve the coating electrode life.Deposition current, deposition voltage, electrode rotation speed, bar EDM electrode surface affect the speed of multi-layer coating deposited the main process parameters. Deposition voltage is the greatest impact. Nickel coating deposition optimum parameters are: deposition current value of 20A, deposition voltage of 7.5V, speed at the 40r/min-60r/min electrode between the bars speed of 3000r/min. The best ceramic layer deposition of metal deposition process parameters are: deposition current value of 20A, deposition voltage of value of 7.5V, speed at 20r/min electrode between the bars speed of 3500r/min.The maximum hardness value of coated electrode is 778HV, much higher than the hardness of Cu-Cr-Zr substrate. Coated electrode face and the cross-section microstructure and composition analysis showed that: a better coating quality surface does not see any form of crack, porosity and other defects exist. The structure of coating includes metal ceramic layer / metal ceramic + Ni layer / Ni layer / Ni + Cu-Cr-Zr layer / Cu-Cr-Zr body.This experimental results show that: the life of uncoated electrodes at least 800 times, while the life of coated electrodes at least 2,000 times, compared to the uncoated electrode, coated electrode life increased by about 2.5 times. Analysis, coated electrodes to improve the life of resistance spot welding of galvanized steel is coated to improve the main mechanism of resistance to plastic deformation of the electrode capacity and limits of zinc and metallurgical reaction between the electrodes. Improve the resistance spot welding electrode matrix strength and resistance to plastic deformation capacity, improving coating composition, structure, designed to improve the coating and substrate bond strength and coating performance, spot welding electrode life can be further enhanced.