Microstructure Evolution And Electroplating Characteristics Of Phosphor Copper Anode

In this paper,a phosphor copper anode with a diameter of 28mm for electroplating was fabricated by continuous extrusion-upsetting and direct upsetting.Firstly,the microstructure and texture evolution of phosphor-copper anode during different forming processes were studied by using electron backscattering diffraction technique.Then the effects of phosphorus content in the phosphor-copper anode,the plating operation conditions and the phosphor-copper anode formed by two different processes on the plating process and the properties of the coating were studied by using Hastelloy cell experiment.Finally,the electrochemical behavior of the phosphor-copper anode under the two different processes was studied by using a three-system electrochemical workstation.The main findings are as follows:By analyzing the microstructure and grain size,it is found that the original microstructure of the upper lead rod is mainly columnar grain and central equiaxed grain,and the grain boundary angle is mainly low angle grain boundary.In the process of continuous extrusion upsetting,after continuous extrusion,the grains of the casting rod are transformed into recrystallized grains and annealing twins,and the grain boundary angle is mainly high angle grain boundary.After upsetting,the annealing twins almost disappear,the recrystallized grains decrease,and the deformed grains are mainly formed.The grain boundary angle changes to the low angle grain boundary.In the direct upsetting process,the original microstructure is broken unevenly,mainly composed of a large number of deformed grains and a small number of recrystallized grains.The grain boundary angle remains low angle grain boundary.The average grain size in the upper casting rod is 248μm.After continuous extrusion and upsetting,the average grain size of the sample is 1.5μm,and the grain refinement is uniform.After direct upsetting,the maximum grain size of the sample reaches 68.4μm,and the minimum grain size is 0.2μm.So the grain size is not uniform.Different forming processes produce different textures.The main composition of the casting rod texture is（001）<110>.After continuous extrusion,the texture in the sample is（001）<100>.After upsetting,there are mainly<001>and<111>fiber textures in the sample.After direct upsetting,（110）<112>texture is the main texture in the sample.The content of phosphorus in phosphorous copper anode has a great effect on electroplating.When the phosphorus content in the phosphorous copper anode is0.0475%,the anode slime in the tank is the least,and the macroscopic morphology of the coating has no burning and pitching.Its microscopic morphology is compact,uniform,smooth,without concave and convex phenomenon.So the electroplating effect obtained by electroplating is the best.The black film formed in the electroplating process was analyzed by EDS and XDR.The results show that the black film contains Cu₃P,Cu SO₄?5H₂O of crystal,and other non crystal.Temperature and current density have great influence on electroplating.The thickness of the coating increases with the increase of current density,but decreases when the current density exceeds a certain value.The surface roughness of the coating increases with the increase of current density.With the increase of temperature,the anode surface is more easily passivated.When the temperature is 40℃,the coating shows smooth,bright,and the roughness is the lowest.No matter at different temperature or different current density,the electrocrystalline plane of the coating is mainly（220）or（111）plane.The phosphorous copper anode formed by continuous extrusion-upsetting process shows better effect in electroplating.Under the same electroplating parameters,no matter from the macroscopic and microscopic morphology of the coating,or from the three-dimensional morphology and roughness of the coating,the surface of the coating obtained by continuous extrusion-upsetting of the phosphorous copper anode has no burning,pitting.The surface of the coating is smooth,bright.The roughness is the lowest.So the phosphor copper anode formed by continuous extrusion-upsetting process is more suitable for electroplating anode material in acidic sulfate base plating bath.In electrochemical behavior analysis,both in terms of anode polarization curve,cyclic voltammetric curves,the apparent activation energy,or constant electric potential oxidation,continuous extrusion-upsetting molding of phosphor copper anode has better dissolution features with the features of passivation of harder.The phosphorous copper anode formed by continuous extrusion-upsetting process is more suitable for electroplating in acidic sulfate base bath.