Research On Preparation And Performance Of Weldable Chromium Plate

Chromium plate is a functional material coated with chromium layer on the surface of cold-rolled low-carbon steel sheet.With its low production cost,excellent corrosion resistance and wear resistance,good appearance of decorative,chromium plate gradually replaced part of the tin plate.However,an insulating chromium oxide layer would cause poor weldability which is on the surface of the chromium plate.So,the chromium oxide layer would be removed by special welding equipment or by grinding when chromium plate is welding.After grinding,the corrosion resistance of chromium plate will be worse,and grinding dust will bring environmental problems.Thus,This article attempts to develop the weldable chromium plate without grinding by controlling morphology of chromium coating.And,this article focuses on the research of the discontinuous chromium and granular chromium plating technology.By SEM,XRD,electrochemical workstation and other methods,morphology and properties were screened to determine the technological parameters of the discontinuous and granular chromium,and investigate their weldability.The discontinuous chromium coating was prepared by high current density electroplating for a short time firstly and then low current density electroplating for a long time.Its performance was characterized by SEM-EDS,XRD,and electrochemical measurements.The results are shown as follows:(1)The content of chromium plate increases linearly with the increase of electroplating time.When the chromium content is 150mg/m~2,the porosity and the proportion of exposed iron in chromium coating are less.In addition,corrosion resistance and weldability change little with the increase of chromium content;(2)The chromium oxide is the main reason for the poor weldability of chromium plating;(3)The optimal electroplating condition is that high current density is 50A/dm~2 and corresponding electroplating time is 0.2s,low current density is 30A/dm~2 and corresponding electroplating time is 1.6s.The discontinuous chromium coating formed under optimal condition exposed iron evenly.The proportion of exposed iron on discontinuous chromium coating is higher than that on continuous chromium coating,so the former has slightly poorer corrosion resistance and better weldability.(4)The EDS shows that the chromium deposit dispersedly after high current density electroplating for short time and the coverage area of chromium changed little after low current density electroplating for long time.The coverage area of chromium on discontinuous chromium coating is less than that on continuous chromium coating.The granular chromium was prepared by intermittent electroplating and the effects of process parameters on the morphology and properties were investigated by means of SEM-EDS,XRD,electrochemical and weldability test.A formation mechanism of granular chromium was also put forward.The results show that the granular chromium was dispersed on the continuous platelike chromium evenly.The characteristic diffraction peaks of the granular chromium was the same as the platelike chromium,but the former shows the preferred orientation of Cr(211)crystal face.The current efficiency of intermittent plating was higher than that of continuous plating.Prolonging the current break time and the second electroplating time will increase the density of granular chromium,decrease the brightness of the coating,but current density of the second electroplating had no obvious effect on that.The chromium oxide was not related to the formation of granular chromium,and local passivation was the cause of its formation.Compared to the common chromium plate,granular chromium was provided with better corrosion resistance and excellent weldability.Meanwhile,the granular chromium could meet welding requirements because of its contact resistance was much smaller than the common chromium plate.