<論文>Cl^-を含むH_2SO_4溶液中におけるAl-Zn-Mg合金の応力腐食割れ

概要

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Stress corrosion cracking (SCC) of solution-treated Al-Zn-Mg alloy wasmainly examined in O.2N-H,SO, +7.2XlO-3M-NaCI (Solution-A) and 0.4N-H,S04+2.4xlO-3M-NaCI (Solution-B) solutions in relation to pitting potential, crackinitiation sites and crack morphology. Pitting potentials (V c) obtained fromcurrent-time curves under various potentials were at -O.78V in solution-A, andat -O.68V in solution-B. The time to fracture decreased with an increase of appliedpotential in both solutions. It seems that the critical potential for SCCcorresponds to the pitting potential under stress (V'c σ). Transgranular SCCwas observed in both solutions. The crack directly initiates on the surface inthe range of V' c σ - V c, and ini tia tes a t the bottom of pits in the range of V c-Vc' (potential which crack growth rate equals to pit growth rate). Mechanicalfracture occurred in the potential above V c'. Cracks initiating from thebottom of pit stops growing below the protective potential (E R ). Therefore,it is necessary for SCC that dissolving pits be present. The crack path is atthe grain boundary at pH=3.3 depending on the pH, however, crack and pittingpotential does not exist at pH =5.8.
秋田大学の論文