Preparation And Corrosion Behavior Of Poly-dopamine/Cu Composite Coating On AZ31 Magnesium Alloy

Magnesium and magnesium alloy,as the light metal material,has obvious advantages in processing and manufacturing owing to their advantages,such as light weight,high heat dissipation capability,good electromagnetic shielding performance,good machinability and anti-deformation ability,high strength,nontoxic,easy recovery.With the development of science and technology,magnesium alloys have been widely used in the fields of electronic intelligent products,national defense,medical equipment and so on.However,the chemical and electrochemical properties of magnesium alloys are relatively active,which leads to the oxidation and corrosion of magnesium alloys.Therefore,it is an important research direction to improve the corrosion resistance of magnesium alloy by proper methods.In this paper,in order to improve the corrosion resistance of AZ31 magnesium alloy,the poly-dopamine / copper composite coating was prepared by different methods.First of all,the surface of the AZ31 magnesium alloy was modified with poly-dopamine film.It was characterized by X-ray photoelectron spectroscopy(XPS).Secondly,copper film was fabricated on poly-dopamine modified AZ31 magnesium alloy surface through electroless plating method.To optimize condition,the effect of pH value,concentration of reducing agent and reaction temperature on the stability of electroless plating solution was investigated.The performance of the polydopamine / copper composite film was tested by electrochemical workstation,scanning electron microscope,X-ray energy spectrum,X-ray diffraction spectrum and tape test.The results showed that: the bath solution consist of 50 mM/L copper chloride,50mM/L EDTA and 0.1 mol/L boric acid.Under the condition of pH 12,water bathing at 35℃ and agitation,50 mM/L dimethylamino borane solution,the ratios of the volume to the bath solution is 25%,was added into the bath solution.With above conditions,a complete bright poly-dopamine / copper composite film can be prepared on the surface of AZ31 magnesium alloy sample.The surface morphology of the composite film shows a micro / nano size lamellar structure,and has good bonding property with the substrate.The film can achieve long-term stability of superhydrophobic by assembling stearic acid modified to and super hydrophobic film by electrochemical test showed that the modified magnesium alloy corrosion potential of magnesium alloy compared with bare positive shift of about 240 mV,the corrosion current density decreased two orders of magnitude,the corrosion resistance is improved obviously.Finally,the preparation of poly-dopamine / copper composite coating on the surface of AZ31 magnesium alloy was investigated by electroplating.The optimum electroplating conditions were determined by adjusting the current density and electroplating time.The properties of the composite films were tested by electrochemical workstation,scanning electron microscope,X-ray energy spectrum,X-ray diffraction spectrum and tape test.The results show that when the current density is-1.5 A·dm-2 and the plating time is 900 s,the coating with uniform and bright color can be prepared on the surface of magnesium alloy samples.The surface morphology of the composite film is a micro / nano sized lamellar structure.The water contact angle shows the film is hydrophobic.When compared with that of bare alloy,the Ecorr value of composite film modified samples shifted towards positive direction by 134 mV and Icorr can be reduced in an order of two.