Research Of Corrosion Behavior Of AZ31 Magnesium Alloy With Different Gd Contents

As a kind of structural material,magnesium alloys have attracted the attention of the automotive industry,electronics industry,aerospace industry and other industries due to its excellent properties,especially for the current world where resources and energy are vanishing and the environment pollution is becoming more and more serious.However,the poor corrosion resistance of magnesium alloy limits its application in industry at a certain extent.So far,related researchers have done a lot of researches regarding to the corrosion and protection of magnesium alloys,and have also achieved certain results,but the understanding of the corrosion mechanism of magnesium alloy is still not perfect,leading to the failure of its large-scale industrial applications.The four groups AZ31 magnesium alloys with different Gd contents in the experiment was smelted and produced in well type resistance furnace under the protect of Ar gas,and then the microstructure and phase composition ofAZ31-xGd?x=0,3.12,4.12,4.78?alloys was characterized by OM,SEM,EDS and XRD.The weight-loss tests and electrochemical experiments for the specimens were carried out in the neutral solution of 3.5% Na₂SO₄,at room temperature,and at the same time,the atmospheric corrosion experiments were done by exposing the specimens to the open air in Taiyuan City.After the best content of Gd was determined,the corrosion behavior of AZ31-4.12 Gd alloy in the Na₂SO₄ solutions with different pH values was also explored.The variation of the surface morphology of specimens before and after the removal of the corrosion products was observed by SEM,and the phase composition of the corrosion products was analyzed by XRD.Then the effects of Gd addition on grain size,the second phase and corrosion rate were researched,and on this basis,the corrosion behavior of AZ31-4.12 Gd alloy in the Na₂SO₄ solutions with different p H values was also further analyzed.There is no doubt that the acquired date in this experiment will contribute to large improve magnesium alloys,corrosion resistance and expand their application fields.The following conclusions were reached:1.In the weight-loss tests,the corrosion rates of alloys significantly decrease with the addition of Gd.Especially when the Gd content reaches4.12%,the corrosion rate of alloy is the least,only 0.675mg/?cm2.d-1?,compared to 4.572mg/?cm2.d-1?without the addition of Gd,the corrosion rate of alloy decreases by about 85%.2.In the electrochemical tests,the addition of Gd increases theself-corrosion potential and reduces the corrosion current density.Especially when the Gd content reaches 4.12%,the self-corrosion potential increases from-1.6987 V to-1.5966 V and the corrosion current density decreases from6.7372×10-4mA to 2.9315× 10-4mA.In addition,the experimental results of the impedance spectra are in good agreement with the experimental results of the polarization curves.3.The addition of Gd,on the one hand,refines the grain size and reduces the micro-galvanic corrosion between the matrix and precipitates,on the other hand,it has also changed the quantities and distribution of the second phase in the matrix,which is equivalent to play a role to reduce the corrosion current density.At the same time,the newly formed Al2 Gd phase and the Gd atoms dissolved in the matrix generate a anticorrosion film on the surface of the specimens,which is similar to coating,so as to improve the corrosion resistance of the alloy.4.After AZ31-4.12 Gd alloy immersed in different pH values Na₂SO₄ solutions,with the increase of pH values of solutions,the corrosion rates of the alloys decreases continuously.In addition,the increase of pH value improves the self-corrosion potential of the substrate and reduces the corrosion current density in the corrosion process.Especially when the pH value of solution is 12,the self-corrosion potential of alloy is the maximum and the corrosion current density is the minimum.These results indicate that the corrosion resistance of the alloy increases with the increase of pH values of solutions.