Preparation And Properties Of Aluminum-Based Films On Magnesium Alloy(AZ91D)

Green development is the theme of today's times.As a green environmental protection engineering material in the 21st century,magnesium alloy,with the continuous expansion of its application field,how to extend the service life of magnesium alloy and solve the problem of its poor corrosion resistance has become an important subject to be urgently solved.In this paper,the electrochemical properties of AlCl₃-EMIC(molar ratio 2:1)ionic liquid electrolyte were studied,the aluminum film,graphene and graphene/gold composite aluminum film were prepared on magnesium alloy by electrodeposition,and the aluminum film and aluminum/cerium oxide/aluminum composite film prepared on magnesium alloy by magnetron sputtering and their properites were discussed.The main findings are as follows:1 Electrochemical properties of AlCl₃-EMIC ionic liquid:the electrochemical workstation CHI660D is used to measure the C-V curves of EMIC ionic liquid at different scanning rates of 30 mV/s,50 mV/s,70 mV/s and 90 mV/s,respectively.Epa moves positively with the increase of sweep speed,which indicated that the electrode process was a quasi-reversible process.Linear regression was made between the values of the peak value of the reduction current | ipc | and the peak value of the oxidation current | ipa | and the square root of the sweep speed V1/2.It was found that the values of the | ipc | and | ipa | were positively correlated with V1/2,which indicated that the electrode process was is a reversible process controlled by diffusion.And the effects of temperatures on electrochemical properties were studied,as can be seen from C-V curve results,with the temperature rising to 70?,the initial reduction potential Einltial is moving to-0.75 V,indicating that the stronger reduction ability of AlCl₃-EMIC solution is at 70?.In order to improve the quality of Al film electrodeposited by AlCl₃-EMIC ionic liquid,both graphene and graphene/gold with their excellent electrical properties were added to the ionic liquid as additives.Combined with the results of C-V curve,it is considered that the electrode process in G and G/Au-EMIC ionic liquid is a quasi-reversible process.The electrochemical performance was enhanced with the increase of temperature(40?70?).2.5 g/L was the optimised experimental condition for graphene(G).The addition of(0.5?2.5 g/L)G/Au increases the values of Einitial,|ipc|,Epa and | ipa | in EMIC ionic liquid,which indicates that the addition of G/Au is a feasible method to improve the electrochemical properties of ionic liquid.2 Both A1 films and G or G/Au-Al composite films on Mg alloy were prepared by electrodeposition in AlCl₃-EMIC ionic liquid.Combined with the results of Atomic Force Microscopy(AFM),X-Ray Diffractometer(XRD)and electrochemical properties,it can be seen that when the deposition potential is at-0.8 V,the surface average roughness of Al film with compact and smooth surface is the minimum value of 23.2 nm,and the average grain size of Al films under different deposition conditions is about 40 nm.Better corrosion properties such as Ecorr(-0.921 V),jcorr(1.07×10-3 A/cm2),| Z | f=0.1HZ(2.0×102?·cm2)can be obtained for Al films at-0.8 V with appearence of passivation region by measuring polarization curves and electrochemical impedance spectra.Especially,Al composite films electrodeposited by G or G/Au-AlCl₃-EMIC solution show good electrochemical performance due to their addition.Additionally,surface pretreatments including anodic oxidation,dilute phosphoric chemical acid,Zn and Al metal sublayers has been carried out to improve the growth of susequent Al films on Mg alloy.Results show better corrosion resistance for Al films deposited after differrent surface pretreatments on Mg alloy.Amongst all methods,both anodic oxidation and Al sublayer show better surface morphological such as Ra?20.0 nm and larger positive corrosion potential such as Ecorr?-0.755 V by AFM morphology observation and electrochemical performance test,suggesting that suitable surface pretreatments for Mg alloy are necessary for the improvement of Al films.3 Both Al films and Al/CeO₂/Al composite films on magnesium alloy were deposited by magnetron sputtering,and effects of processing parameters such as negative bias voltage(-200?-400 V),sputtering power(100?200 W),as well as substrate heating temperature(50?200?)on their structural,morphological and corrosion resistance properties via orthogonal test were investigated.It is found that the optimised processing parameters at-300 V,200 W and 50? are obtained,with smaller surface roughness Ra of 11.6 nm and larger positive corrosion potential Ecorr of-1.411 V of the 40 nm-grain-size Al film.Moreover,there is the change of film stress mechnism from tensile stress at 50?150? to compressive stress at 200?.In Al/CeO₂/Al sandwich structure composite films with compact structure and smooth interface,the corrosion current density is increased by two orders of magnitude compared with Mg alloy substrate,but heat treament temperature above 350? will result in obvious change in the structurre and morphology of Al/CeO₂/Al films with poor corrosion resistance.