Corrosion Behavior Of Extruded And Forged WE43 Rare Earth Magnesium Alloy In NaCl And Na₂SO₄ Solution

Magnesium and magnesium alloys have many advantages such as high specific strength,low density,good electromagnetic shielding performance and biocompatibility,but their simultaneous low strength,insufficient plasticity,and poor corrosion resistance restrict their large-scale engineering applications.Deformation treatment is an effective way to improve the comprehensive properties of magnesium and magnesium alloys.However,the current research on the corrosion of deformed magnesium alloys focuses on the comparison of corrosion resistance before and after deformation,and the relationship between the microstructure and corrosion behavior of magnesium alloys after different deformation processes.In particular,the corrosion behavior of magnesium alloys in different solutions after different deformation processes is still unclear.In this paper,the commercial extruded and forged WE43 rare earth magnesium alloys were used as the research objects.X-ray diffractometer（XRD）,optical microscope（OM）,scanning electron microscope（SEM）,transmission el ectron microscope（TEM）,immersion experiment,hydrogen evolution test,weight loss tests and electrochemical tests were applied to systematically compare the microstructure,microgalvanic corrosion behavior,corrosion resistance and electrochemical proper ties of extruded and forged WE43 magnesium alloys in sodium chloride and sodium sulfate solutions.The results show that the extruded and forged WE43 magnesium alloys have the same phases,namely Mg,Mg₁₄Nd₂Y,Mg₂₄Y₅ and Zr,respectively.In the OM and SEM images,the extruded WE43 magnesium alloy exhibits an equiaxed grain structure with complete dynamic recrystallization,and its average grain size is 18μm,whereas the extruded WE43 magnesium alloy has coarse grains with abnormal grain growth,with an average grain size of 40μm.The second phase of the extruded magnesium alloy is uniformly distributed on the surface of the alloy,and its surface area fraction is 4%.Among the two forms of the second phase in the forged magnesium alloy,the large-scale second phase is scattered on the surface of the alloy,and the pearl-shaped second phase is distributed along the grain boundary,and their total surface area fraction is 3.4%.Further TEM tests showed that,except for the plate-like phase existing in the forged magnesium alloy grains,the difference between the second phase of the extruded and forged WE43 magnesium alloy was mainly reflected in the size.In 0.6 M NaCl solution,the corrosion rate of forged WE43 magnesium alloy is much higher than that of extruded WE43 magnesium alloy,and the second phase of the extruded and the forged WE43 magnesium alloy acts as the cathode and forms microgalvanic corrosion with its surrounding magnesium matrix.Different sized second-phase particles in the two alloys may lead to different corrosion behaviors,and the large-scale second phase has a higher electrochemical influence range than the pearl-shaped second phase,which in turn induces strong localized corrosion.The corrosion product films of the extruded WE43 magnesium alloy still maintains a good protective ability after a longer soaking time,while the corrosion product film of the forged WE43 alloy fails in a shorter time.In 0.6 M Na₂SO₄ solution,the corrosion rate of forged WE43 magnesium alloy is slightly lower than that of extruded WE43 magnesium alloy,and the second phase of the extruded WE43 magnesium alloy and the large-sized second phase of the forged WE43 alloy act as anodes to form microgalvanic corrosion with the surrounding magnesium matrix.The corrosion product films formed in the Na₂SO₄ solution of the extruded and forged WE43 magnesium alloys cannot play a good protective role,and the two alloys showed different corrosion rates,which were related to the differences in the microstructures between them.