间歇电沉积粒状铬镀层的过程及其性能

To improve the weldability of the Tin Free Steel, the granular chromium coatings were obtained on the steel by intermittent electrodeposit. The morphology and structure of the granular chromium were investigated and analyzed with scanning electron microscopy (SEM), X-ray diffraction (XRD), and the chromium content of the coatings were measured by the coulomb electrolysis method. The weldability of TFS was evaluated by measuring the contact resistance and observing the welding surface. Experimental results showed that the granular chromium distribute on the platelike chromium evenly. As the current interruption time extends, the density of the granular chromium gradually increases, while the welding resistance decreases. Compared with continuous electrodeposit, the preferred orientation of Cr(211) plane appears on the granular chromium prepared by intermittent electrodeposit. The chromium content of coating prepared by intermittent electroplating was higher than that of the continuous plating under the same charge amount. When the current is interrupted, the discontinuous oxide film is formed to make the layered chromium partially passivated, and the active point preferentially discharges to form dispersed granular chromium. When the pressure keeps constant, the contact resistance of the granular chromium coating is much smaller than that of the conventional chromium coating, and under same welding current, the former can be welded while the latter can't. During the current interruption, the presence of partial passivation contributes to the formation of granular chromium, which improves the weldability of TFS.