Study On Corrosion Behavior Of Magnesium-based Nanocomposites In Different Solutions

Magnesium-based composite materials have many excellent mechanical properties,so they have broad application prospects and have been widely used in medical,transportation and aerospace.The corrosion resistance of magnesium-based composites is an important factor that limits its rapid development,and the current research on corrosion resistance based on magnesium-based composites is not systematic enough.Therefore,it is very important to study the corrosion performance and corrosion mechanism of magnesium-based composites.In this paper,powder metallurgy technology was used to prepare Mg/SiO₂ and Mg/HAP magnesium-based nanocomposites.Optical microscope,scanning electron microscope and laser confocal microscope were used to characterize the microstructure and three-dimensional morphology of magnesium-based composite.The corrosion rate of the composite material was measured by hydrogen evolution,weight loss method,polarization and AC impedance test methods.At the same time,using X-ray photoelectron spectroscopy to quantitatively analyze the composition of corrosion products and scanning Kelvin probe force microscope to analyze the potential distribution of the composite material surface.This paper focusing on the study of the two magnesium-based composite materials in different corrosion solutions Corrosion behavior.The main content is summarized as follows:(1)The influence of the composition of Mg/SiO₂ in 3.5 wt.%Na₂SO₄ solution on its corrosion behavior.The experimental results show that after adding SiO₂ nano-reinforced particles,the corrosion resistance of the composite material is lower than that of pure magnesium.The increase in the mass fraction of reinforcing particles,the worse the corrosion resistance of the material,which is more obvious in the early stage of corrosion.Through optical microscope observation,it can be seen that the added reinforcement particles are mainly agglomerated at the grain boundary,making the grain refinement.The material has more dislocations at the grain boundary and higher energy.The potential distribution on the surface of the composite material shows that the potential at the grain boundary is significantly lower than that of the matrix,which is prone to micro-galvanic corrosion.(2)The effect of the corrosion time of Mg/SiO₂ in 3.5 wt.%Na₂SO₄ solution on its corrosion behavior.The experimental results show that as the immersion time of the composite material in the corrosion solution increases,the corrosion rate of pure Mg,Mg/0.5SiO₂ and Mg/1.0SiO₂ is gradually decreasing.And the influence of the reinforcing particles on the corrosion rate is gradually weakening.Because the magnesium-based nanocomposite material will form a protective film on the surface of the substrate during the corrosion process,which provides a good protective effect for the composite material in the corrosion solution.The components of corrosion products analyzed by X-ray photoelectron spectroscopy are Mg(OH)₂ and Mg CO₃.(3)The corrosion test results of Mg/HAP in 3.5 wt.%NaCl solution show that hydroxyapatite(HAP)reinforced particles reduce the corrosion resistance of the composite material.The chemical formula of HAP is Ca5(PO4)3(OH).With the increase of the mass fraction of the reinforced particles,the corrosion resistance of the materials is going worse.And the longer the composite material is immersed in the corrosion solution,the more obvious the effect of the reinforcing particles on the corrosion rate.Observing the morphology of the microstructure after corrosion by scanning electron microscope,it is found that the corrosion type of the material is mainly intergranular corrosion and filiform corrosion.Observation under the optical microscope shows that the particles agglomerate at the grain boundary.The surface potential distribution of the composite material shows that the electric potential of grain boundary is significantly lower than that of the substrate,which is prone to micro-galvanic corrosion.The corrosion rate of the composite material was measured.It is found that the corrosion rate of the composite material in the sodium chloride solution was very fast.(4)Pure Mg,Mg/0.5HAP and Mg/1.0HAP were subjected to heat treatment at 150?,250?and 350?respectively for 8 h,and then subjected to open circuit potential for 10 min in 3.5 wt.%NaCl solution.And then the Polarization test and AC impedance test were carried.The measurement results show that the current density of the heat-treated sample is greater than or slightly about that of the unheated sample,and the impedance value is lower than that of the unheated sample,which indicates the corrosion rate of the heat-treated samples have not slowed down.And the corrosion resistance of the material has not been effectively improved.(5)After pure Mg has been heat treated at 150?,250?,350?for 30 min and 150?for 90 min,the grain size of pure Mg has not changed significantly from the microstructure morphology.Observe the change of the surface corrosion morphology of the sample during the immersion process of 3.5 wt.%NaCl solution from the macroscopic view.The corrosion resistance of the material after heat treatment has improved.The corrosion resistance of150?-30 min,250?-30 min and 150?-90 min after heat treatment are improved compared with pure Mg without heat treatment from the microscopic corrosion morphology.And it is consistent with the former conclusion from the result of electrochemical test.The greatest improvement in corrosion resistance is heat treatment at 150?-90 min,followed by 150?-30 min and 250?-30 min.This indicates that the material made by this process can improve the corrosion resistance of the material through heat treatment.