The Influence Of Metallurgical Quality And The Corrosion Behavior Of Magnesium Alloys

Due to its advantages such as light weight,high specific strength and stiffness,excellent structural performance and easy to recycle,magnesium alloys have been paid more and more attention and become the most promising metal structure material.However,because the Standard Electrode Potential of magnesium is too low and the density of the oxide film is poor,the corrosion resistance of magnesium and its alloys is poor,which limits its wide application.In this paper,different magnesium alloy samples were prepared by the different metallurgical quality of pure magnesium,and the AZ31and AZ91 magnesium alloys were centrifuged and solidified to obtain solidification samples under different technological conditions,the corrosion behavior,corrosion morphology and related micro-components of each sample were analyzed by salt spray corrosiontest,scanningelectronmicroscopy（SEM）,energydispersive spectroscopy（EDS）.The corrosion characteristics and corrosion mechanism of various samples under different conditions were discussed.The relationship between the metallurgical quality.solidification structure and corrosion characteristics of pure magnesium and its alloys was revealed.The results show that:1.Metallurgical quality has an important effect on the corrosion resistance of pure magnesium especially the content of iron element.the pure magnesium surface with the the 0.0101%content of iron element appeared serious pitting pits,but the corrosion properties of the pure magnesium surface with the the 0.0047%content of iron element is more uniform.Metallurgical quality not only has an important effect on the corrosion properties of pure magnesium,but also has a profound effect on the preparation of magnesium alloy samples,showing a certain hereditary characteristics.Different AZ31and AZ91 magnesium alloy prepared by pure magnesium with different metallurgical quality,the same salt spray corrosion conditions,The corrosion properties of AZ91magnesium alloy containing more iron elements is almost nonuniform.However the low content of iron element is uniform relatively.The samples of corrosion properties are uneven in the AZ31 magnesium alloy,the pure magnesium with the little content of iron element has a deeper pitting pits compared with the high content of iron element.2.Different solidification obtained by different process conditions have an important effect on the corrosion properties of the samples.The maximum depth of AZ91 magnesium alloy corrosion pits decreases from 516μm to 178.5μm with the increase of centrifugal pressure,and the maximum weight loss rate decreases from0.145mg/（mm²h）to 0.05mg/（mm²·h）,The maximum depth of AZ31 magnesium alloy corrosion pits decreases from 275.5μm to 167.2μm,and the maximum weight loss rate decreases from 0.032 mg/（mm²·h）to 0.021 mg/（mm²·h）.As the centrifugal force increases,the structure of magnesium alloy will be refined,and the shrinkage and other defects will be reduced,the organization becomes more compact,and the second phase by the isolated granular Gradually become a continuous mesh in the AZ91 magnesium alloy,which will protect the magnesium alloy matrix,therefore,the corrosion resistance of magnesium alloy has improved.3.With the increase of corrosion time,the weight loss rate of magnesium alloy increases rapidly and finally remains stable.In AZ91 magnesium alloy,the initial weight loss rate is about 0.035 mg/（mm²·h）,the weight loss rate achieve to 0.100mg/（mm²·h）and remain constant after the salt spray corrosion for 30h,the initial weight loss rate of about 0.013mg/（mm²·h）,and finally reach 0.025mg/（mm²·h）remained unchanged in the AZ31 Magnesium alloy.4.The Energy spectrum analysis result shows that Pitting pits only have magnesium element,this is due to the magnesium matrix and the second phase Mg₁₇Al₁₂ constitute the micro-cell,and the magnesium is preferentially corroded as the anode,and the second phase has been present on the surface of magnesium alloy in the NaCl solution.