| Magnesium alloys are used in the biomedical field due to their close proximity to human bones and their ability to degrade themselves into harmless ions.Although traditional titanium alloys,stainless steel and other bone implant materials can meet the mechanical properties of the human body,the release of toxic substances easily causes a series of side effects in the human body.Therefore,the advantages of magnesium alloys in biomedical materials have gradually emerged.However,due to the poor corrosion resistance of magnesium alloys,the recovery period of human bones cannot be satisfied,which greatly limits its application.Polycaprolactone?PCL?is a non-toxic and harmless polymer with good biocompatibility and histocompatibility.It has been widely used in biomedical applications such as tapes,bandages and sutures,and small weight-bearing bone implants.It is worth noting that it can be degraded by the action of microorganisms or enzymes.For example,PCL can be degraded into H2O and CO2 in environment of soil and water within 6-12 months.Therefore,PCL can be degraded in the human body together with the magnesium alloy,and the pain and trouble caused by the secondary surgery can be reduced while satisfying the recovery cycle.However,the weak bonding force between the PCL and the magnesium alloy matrix seriously affects the protection of the coating on the magnesium alloy,so proper pretreatment is required.In this paper,AZ60 magnesium alloy is used as the substrate,and polycaprolactone is used as the organic coating.The phosphating and silane?SCA?pretreatment methods are used to explore the bonding connection and corrosion resistance of layers.After phosphating the magnesium alloy substrate,a layer of PCL organic coating is applied to obtain a calcium phosphorus/PCL composite coating.After comparing the electrochemical properties,immersion properties,surface morphology and other properties of untreated,single coatings and composite coatings,it was found that the composite organic coating exhibited a more positive potential Ecorr=-1.17 V and a lower current density Icorr=2.93×10-7 A/cm2.The potential of the untreated magnesium alloy matrix is shifted by 0.24 V,the corrosion starting point becomes higher,the current density is reduced by two orders of magnitude,and the corrosion rate is greatly reduced.After the composite coating treatment,the amount of hydrogen evolution was lower and the rate was slower.The total amount of precipitation after seven days was0.5 ml,which was 1/8 of the untreated substrate,showing good corrosion resistance.According to the elemental analysis of the energy spectrum,the corrosion products and deposition materials on the surface of the sample are MgO,Mg?OH?2 and calcium phosphate after 7 days of immersion in SBF.Therefore,the composite coating can increase the bonding force between the PCL and the magnesium alloy,and effectively enhance the coating's ability to protect the magnesium substrate.The silane coupling agent KH550 was used as the pretreatment,and the PCL polymer was used as the organic coating to obtain the SCA/PCL composite coating.The electrochemical properties,immersion performance,surface morphology and bonding properties of untreated,single coatings and composite coatings were investigated,and the reasons for the performance changes were studied from the reaction mechanism.The composite organic coating exhibits a more positive potential Ecorr=-0.365 V and a lower current density icorr=2.93×10-7 A/cm2,which is shifted nearly 1 V more than the untreated magnesium alloy substrate and current density reduced by two orders of magnitude.When the surface of the substrate is coated with a composite coating,the rate of hydrogen evolution is significantly suppressed.After 7days,the amount of hydrogen evolution is only 1/4 of the substrate,1/2 of the single coating,showing excellent corrosion resistance.The scratch test showed that the silane treatment played a good connection between the magnesium alloy and the PCL organic coating,which enhanced the bonding force.In summary,the composite coating exhibits great adhesion and corrosion resistance. |
PDF Full Text Request