Investigation On Preparation Of Multilayer Graphene By Template Method And Its Effect On Anodic Oxidation Coating Modification Of AZ31 Magnesium Alloy

Mg alloys are widely applied in fields of aerospace,automotive and 3C electrical products for their low specific gravity,high seismic performance and excellent conductivity.However,the poor corrosion resistance seriously limited its application.Therefore,the investigation of corrosion and protection of magnesium alloys has important significance of scientific and practical.In this paper,based on the preparation of multilayer graphene by using nano-tungsten carbide as templates,facing the shortage of porous structure of anodic oxidation coating of magnesium alloy,the multilayer graphene was added into the electrolyte to modify the anodic oxidation coatings.And the modification mechanism was explored.Firstly,the tungsten carbide/multilayer graphene compound particles with high specific surface area and high dispersing property were prepared by template method.Then the multilayer graphene is separated from the tungsten carbide/multilayer graphene compound particles.The morphology and performance of multilayer graphene were characterized by scanning electron microscope?SEM?,transmission electronic microscopy?TEM?,X-ray diffraction?XRD?,transmission electronic microscopy?TEM?,infrared and low temperature nitrogen adsorption desorption isotherm.Secondly,anodic oxidation coating of AZ31magnesium alloy with multilayer graphene was preparated.The effect of the multilayer graphene concentration,processing current and processing time on the microstructure and corrosion resistance of the anodic oxidation coating on AZ31 magnesium alloy were investigated.Furthermore,the modifying mechanism of multilayer graphene on anodic oxidation coating of AZ31 magnesium was explored.?1?The precursors of H₂WO₄/CNTs were prepared by the template method using CNTs as template and Na₂WO₄ as tungsten source.Furthermore,the CNTs was oxidized and the H₂WO₄ was carbonized to tungsten carbide using ethanol/methanol mixture as reducing agent and carbon source.The excess and remaining carbon was deposited on the surface of tungsten carbide to form multilayer graphene,and in which way tungsten carbide/multilayer graphene compound particles was successfully prepared.Multilayer graphene was separated from tungsten carbide/multilayer graphene compound particles by mixture of 5mLHNO₃+5mLHF+10mLH₂O.The achieved multilayer graphene has the characteristics of small damage,easy dispersed and large specific surface area.?2?The anodic oxidation coating modified by multilayer graphene was successfully fabricated on the surface of AZ31 magnesium alloy by adding multilayer graphene into the electrolyte.The optimum processing parameters are graphene concentration 0.5g/L,processing current 0.3A and processing time 60 min.?3?Compared with the anodic coating without multilayer graphene,the anodic oxidation coating with multilayer graphene additive is more compact,and the phase is composed of Mg,MgO,MgSiO₃and graphene.The corrosion resistance of the coating is improved obviously.The R₁ and R₂ values from 1.74K?.cm² and 146.90K?.cm² to 79.25K?.cm²and 2108.60K?.cm².?4?The modifying mechanism of multilayer graphene on anodic oxidation coating of AZ magnesium alloy is as following;the addition of multilayer graphene increased the breakdown potential of magnesium oxide,and it inhibit the growth of oxide film.At the same time,the multilayer graphene filled the discharge channel and t hindered he corrosion medium reach the surface of AZ31magnesium alloy substrate.