Study On Microstructure And Corrosion Behavior Of Mg-In Alloys

The magnesium alloy which has the characteristics of low density,high specific strength,electromagnetic shielding and biocompatibility is regarded as the green engineering material of the 21st century.It is one of the materials of aerospace,military weapon,clinical medicine,and automobile and so on.However,the high chemical activity of magnesium can be easily corroded in the humid environment,which is the main bottleneck restricting the application of magnesium alloys.The atomic number of indium element is 49,with low melting point,excellent ductility,stable chemical property,et al.,and indium has a high hydrogenation over potential,which can inhibit hydrogen generation.In this article,the Mg-In binary alloys were smelted.The microstructure and corrosion behavior of Mg-In alloys were studied by metallographic analysis,X ray diffraction analysis,scanning electron microscope,energy spectrum analysis,electrochemical measurement,soaking weightlessness test and X ray photoelectron spectroscopy and the conclusions are as follows:(1)Metallographic microscopic analysis and X ray diffraction analysis of Mg-In alloys with different In contents can be obtained.It can be concluded that the alloy structure is mainly a single-phase structure of alpha-Mg,and the lattice structure is a dense six square structure(HCP)after adding In element to pure magnesium.Due to the larger atomic radius of In,the lattice constant increases,that is,the value of a and C increase.Therefore,the D value of crystal spacing increases,and the diffraction peak moves slightly to the left.The microstructure of as cast magnesium indium alloy is mainly primary dendrite and relatively small.With the increase of In content,the dendrite spacing of alloy firstly decreases and then increases.When the content of indium is about1.1%,the dendrite spacing of alloy is the smallest.(2)The effects of the content of In elements on the corrosion properties of the alloy were investigated by electrochemical testing,soaking weightlessness test,scanning electron microscope analysis and X ray photoelectron spectroscopy.The corrosion mechanism of magnesium and indium alloy with different content of magnesium and indium alloy was discussed.The results show that adding indium in pure magnesium,the corrosion resistance of alloy is improved obviously.In the three alloys with different In content,when the content of indium is 1.1%,the corrosion resistance of Mg-In alloy is the best.The mechanism is that on the one hand,with the addition of indium elements which is high hydrogen overpotential metal,leading to the resistance of the hydrogen evolution reaction is not easy to be carried out on the surface corrosion of the alloy,thus reducing the corrosion.On the other hand,the X ray photoelectricity spectrum analysis shows that the indium in the corrosion product is in the+3 valence of indium hydroxide.The indium hydroxide can fill into the loose crevice of magnesium hydroxide,and can increase the integrity and tightness of the corrosion product film on the alloy surface.(3)The corrosion resistance of Mg-1.1In alloy in NaCl solution with different pH was tested and the surface corrosion morphology of the samples after weightlessness was observed by scanning electron microscope.It can be concluded that the corrosion resistance of Mg-1.1In alloy becomes better with the increase of pH value of the solution.This is because the surface corrosion products can be stabilized in the higher pH solution and increase the density of the corrosion product film.(4)The corrosion resistance of Mg-1.1In alloy in NaCl solution with different concentration was tested and the surface corrosion morphology of the samples after weightlessness was observed by scanning electron microscope.It was found that the corrosion resistance of Mg-1.1In alloy changed better with the increase of NaCl concentration in the solution.Because the ion exchange between the film is suppressed at the high concentrations,leading to lower the rupture of the passivation film critical concentration when the corrosive Cl~-reaches the surface of the saturation.On the other hand,alloy forms a denser protective layer to improve corrosion resistance which reduces the corrosion rate and improves electrochemical corrosion resistance of the alloy.