Investigation Of Stress Corrosion Behavior Of Fine-grained AZ31 Magnesium Alloy Fabricated By Friction Stir Processing

Magnesium alloys have been attracted to many field such as aviation and aerospace due to their low density,high specific strength et.,but largely restricted in industrial application by their poor corrosion resistance.While researchers abroad and domestic have done many investigations,the corrosion behavior and mechanism featured different microstructure has been little reported.Hence this paper,based on the magnesium alloy with different grain size and grain orientation fabricated by Friction Stir Processing technique(FSP),investigated the static corrosion behavior and Stress Corrosion Cracking(SCC)when serving under external stress of AZ31,by proceeding electrochemical measurement technology,immersion tests and neutral salt spray tests(NSS)and analyzed by scanning electron microscope(SEM)and X-ray diffraction technology(XRD),.The static corrosion behavior of AZ31 in 0.1M NaCl solution is investigated.Results showed different microstructure generated different corrosion behavior.When the grain size is same,specimens with FSP texture have smaller corrosion current density than those with rolling texture(BM),and the corrosion rate in early stage is more significant with descending to lower than BM after certain time.In NSS tests,specimens with FSP texture generated uniformly distributed corrosion products in bulk and needle-shape,contributing more protecting affect to increase corrosion resistance.When the grain orientation is the same,400 rpm specimens with finer grains have smaller corrosion current density than the 1600 rpm specimens with coarser grains,and the corrosion rate in early stage is more significant with descending to lower than coarser specimens after certain time.In NSS tests,fine grained specimens produced fine and closely distributed corrosion products,offering better protect to inner matrix resulting an increase in corrosion resistance.By conducting slow strain rate tests(SSRT),it is found that magnesium alloys is susceptible to distilled water.The hydration of oxidation film let electrolytic hydrogen atom reside at both the surface and interior of the matrix,causing the SCC in specimen,which pronounce the SCC mechanism in distilled water is dominant by hydrogen embrittlement(HE).In 0.1M NaCl aqueous solution,pit corrosion and filiform corrosion can be observed on the specimens surface,leading inner magnesium matrix to stress corrosion failure predominant to anodic dissolution and hydrogen embrittlement,in which FSP texture and coarser grains are more susceptible to SCC.