The Study On ZrB₂-TiB₂ Composite Coating On Surface Of Spot Welding Electrode By Electro Sparking Deposition

In order to improve the lifespan of electrodes used for spot welding galvanized steel plates, the paper proposes ZrB2-TiB2 composite ceramic were deposited as a coating on the electrode surface. ZrB2-TiB2 rod(discharge electrode) was prepared by mechanical alloying and atmosphere sintering, ZrB2-TiB2 composite coating was deposited on the electrode surface by electro-sparking deposition. The XRD of Zr, Ti, B,Ni mechanical alloying showed that, mixed powders can’t react chemically in the effective milling time(20h). The initial powders were uniformly mixed, and the powder particles were refined. Differential Thermal Analysis of the mixed powders after milling20 h showed that, the mixed powders were reacted completely and converted into ZrB2-TiB2 at 1472℃, therefore atmosphere sintering temperature was determined as1500℃. The orthogonal tests were based on the factors effecting coating, the results showed that when the voltage was 24 V, the capacitance was 2000μF, deposition time was 120 s, the quality of ZrB2-TiB2 coating deposition maximum. The XRD analysis showed that the coatings consist of ZrB2 and TiB2 phase. ZrB2-TiB2 was deposited onto their surface after pre-coating nickel as an intermediate layer. Ni+(ZrB2-TiB2) double coating can improve the defects of Zr B2-TiB2 composite coating. The spot-welding life of ZrB2-TiB2 composite coated electrode and double coated electrode were tested using a spot-welding machine. The result showed that the life of the double coated electrode was 3000 spots, which was much larger than that of the composite coated electrode(2300 spots). ZrB2-TiB2 composite coating had a lot of internal defects in the manufacturing process, resulting in ZrB2-TiB2 composite coating can’t fully play a protective role. Ni+(ZrB2-TiB2) double coating failure can be divided into two phases which are ZrB2-TiB2 composite coating failure and Ni layer failure.