Study On Pulsed Electrolytic Coloring Process And Properties Of Pure Aluminum In Ferrous Sulfate Solution

Aluminum and its alloys are widely used in production and living because of their small density,easily processing,good physical and mechanical performance.Aluminum is active metal element and is easy to create a compact natural oxidation film in air and aerobic environment and is protected.However,the natural oxidation film is too thin,uneven and discontinuous and is limited in practical application.Aluminum and its alloys are needed to be surface treated for improving their abrasive resistance,corrosion resistance,decoration,function,etc.Anodic oxidation and electrolytic coloring are usual methods.In the usual technology of anodic oxidation and electrolytic coloring of aluminum and it alloys,the problem of color monotonic and a few kinds of coloring solution are exist.The technology of pure aluminum was electrolytic colored by a numerical control pulse power supply was researched in this thesis.Firstly,Aluminum was pulse electrolytic colored in silver sulfate solution.The technologic parameter was made sure to offer a rough technologic range for subsequent pulse electrolytic colored in ferrous sulfate.Experimental results showed that the optimum technologic parameters of aluminum pulse electrolytic coloring in silver sulfate solution were: negative voltage 14 V,positive voltage 13 V,total duty cycle 30%,work frequency 50 Hz,negative duty cycle 70%,positive duty cycle 30%.In the research of technologic condition of aluminum electrolytic colored in ferrous sulfate solution,Single factor experimental method was adopted.The color departure value of the coloring film relative to black color was as standard.The optimum technologic parameters of aluminum pulse electrolytic coloring were: FeSO₄·7H₂O 30 g/L,?NH₄?₂SO₄ 15 g/L,H₃BO₃ 15 g/L,pH of coloring solution 3-4,work frequency 50 Hz,total duty cycle 40%,positive duty cycle 30%,negative duty cycle 70%,positive voltage 12 V,negative voltage 16 V,coloring time 10 min.The coloring film was nigger-brown,uniform and bright.By qualitative assessing coloring film of aluminum pulse electrolytic colored in ferrous sulfate solution,the results showed that the film thickness of colored sample prepared at optimum technologic condition was about 12 mm.The film had good abrasive resistance,corrosion resistance and thermal stability,but its hot crackability was not good.By physical testing pure aluminum sample,anodic oxidized sample and pulse electrolytic colored sample,respectively,the results showed that the macrocosmic surface forms of the anodic oxidized sample and pulse electrolytic colored sample were smoother and leveler than that of the pure aluminum sample.By SEM,EDS,and XRD testing,the microcosmic surface form of the pulse electrolytic colored sample was much more flat and compact.The pulse electrolytic colored film containing iron element.By polarization curves and AC impedance figures of electrochemical test,it showed that the pulse electrolytic colored sample had excellent corrosion resistance.