The Effect Of Tensile Deformation On The Stress Corrosion Behavior Of AZ31 Magnesium Alloys

Magnesium alloy is called"the lightest structural material"by its low density,high specific strength and high specific rigidity.Meanwhile,good biocompatibility,non-toxicity,and in vivo degradability make magnesium alloys have broad prospects and positive significance in the field of green development and medical health.Practical utilizations of magnesium and magnesium alloys are limited due to their poor room temperature formability and poor corrosion resistance.As a wrought magnesium alloy,it faces various corrosive environments in engineering and medical applications.In this study,AZ31 magnesium alloy rolled sheet(NaCl solution,Na₂SO₄ solution and simulate body fluid(SBF)solution)is used to explore the influence of tensile deformation in different corrosive media on the corrosion behaviour of magnesium alloy sheets and their mechanism.The results show that:(1)The microstructure of AZ31 alloy is affected by tensile deformation along the rolling direction(RD),the increase in strain does not affect the average grain size and surface roughness.However,the basal texture intensity increases with the increase of strain.When the strain exceeds 12%,twins are generated and increase as the amount of strain increases.With a strain of 6%,there is almost no change in the average grain size when stretched in different directions.(2)The anion type has a significant effect on the corrosion behaviour of magnesium alloys.Compared with SO₄^2-,Cl^-has a smaller ion radius and is more corrosive for AZ31magnesium alloy rolled sheet.The weight loss corrosion rate of rolled AZ31 magnesium alloy sheet in the two solutions differs by more than 50%.(3)In NaCl solution,as a high surface energy site,twins promote galvanic corrosion,destroy the integrity of the basal texture,and make the corrosion inhibitory effect of the basal texture disappear.Conversely,twins that work as grain boundaries hinder electron migration in the Na₂SO₄ solution.(4)In different corrosive media,there are obvious differences in the effects of tensile strain along RD on the corrosion behavior of AZ31 magnesium alloy.In the NaCl solution:Corrosion resistance decreases after tensile deformation compared with undeformed sample.Before reaching 12%strain,the corrosion rate of AZ31 magnesium alloy sheet first increases and then decreases,and reaches its maximum value at 3%strain.When the strain exceeds 12%,internal defects and twins promote galvanic corrosion,and the corrosion resistance declines rapidly.In the Na₂SO₄ solution:The corrosion resistance of AZ31 magnesium alloy sheet increases first and then decreases with the increase of tensile strain,and reaches the highest at 15%strain.In the SBF solution:There is no obvious linear relation between corrosion resistance and tensile strain.As the strain increases,the corrosion resistance increases and then decreases and increases again(in a zigzag shape).The 6%and 12%strains are the two inflection points on the curve.The self-corrosion current in SBF solution is much larger than that in the other two solutions.(5)Compared with tensile strain,the tensile direction has less influence on the corrosion behavior of AZ31 magnesium alloy sheet.In the NaCl solution:The corrosion resistance of AZ31 magnesium alloy sheet increases first and then decreases with the increase of the angle between the tensile direction and the RD.The corrosion resistance is the best when the angle is45°.In the Na₂SO₄ solution:The change trend of corrosion behavior is the same as that in NaCl solution.The corrosion resistance is best when the tensile direction and the RD are at an angle of 45°.In the SBF solution:With the increase of the angle between the stretching direction and the RD,the change of the corrosion resistance shows a W shape.The valleys appear at angles of 30°and 60°,and the peak appears at the angle of 45°.