Corrosion Resistance And Corrosion Wear Behavior Of Anodic Oxidation Coating On 70 Series Aluminum Alloy

Anodic oxidation is a very common surface treatment technology of aluminum alloy,with simple process,economical and practical characters and so on.At present,the research of aluminum alloy anode oxidation film is mainly focused on sealing hole and corrosion resistance.There is very little study about the corrosion wear of film,especially researching in corrosive environment.In real life,the use environments of materials are not single usually,so the study of friction wear under corrosive environment will have more practical significance and use value.In this article,the sulfuric acid solution was chosen as the electrolyte to anodize 7075 aluminum alloys.Then the oxidation samples were post-processed with chemical plating,and the thickness,hardness,morphology,composition and corrosion resistance of film were measured and analyzed.Finally,deionized water and 3.5%NaCl solution were selected as the liquid medium to study friction and wear behavior of the film in water and saline water.The main work and results obtained are as follows:1.Digital multiple coating thickness gauge,the microhardness meter,SEM,EDS and XRD were used to measure and analyze the film thickness,hardness,and appearance structure.The results show that oxidation film has double structures and some loose holes,and thickness and hardness of the film will be affected by changes of oxidation time,current density and sulfuric acid concentration.2.The aluminum alloy oxide samples without sealing,chemical plating and sealing dichromate were carried on doing immersion experiment(in the acid,the alkali,and the salt)and electrochemistry experiment(open circuit potential and the Tafel polarization curves).The results show the chemical plating can improves the corrosion resistance of the sample,and the corrosion potential increases by 130mV than the non-sealing sample.With oxidation time and sulfuric acid concentration increasing,the corrosion resistance of the film increases at first and then decreases.With the current density increasing,the corrosion resistance of the film gradually decreases.3.The wear condition of the simples in the corrosion medium(salt water)was studied.The results are as followed:The chemical plating samples have much better corrosion wear-ability than simples without sealing.When the load increases,the friction coefficient reduces,and the wear loss changes with fluctuation-style.When the friction speed increases,the friction coefficient changes with fluctuation-style,and the wear loss reduces gradually.If the wear time increases,the friction coefficient and wear loss will both increase linearly.Along with oxidation time of the film increasing,the friction coefficient increases first then declines.However,the current density and the sulfuric acid concentration have little effect on the friction coefficient.With the oxidation time,current density and the sulfuric acid concentration increasing,the wear loss declines firstly and then increases.4.The attrition situation in the water and the interaction between corrosion and wear were studied.The results show that the amount of wear in the water is always less than in the salt water and the friction coefficient in the water is larger than in the salt water.A layer of liquid film will be formed between couple samples when samples are wearing,which has functions on reducing friction coefficient and shear stress.At the same time,the salt water film will also have a corrosive effect on film defects.