Al-Zn-Mg合金の定電位応力腐食割れのワイブル分布を用いた評価

抄録

Effects of controlled potential on fracture time, t_f, crack-initiation time, t_i and crack-propagation time, t_c in the stress corrosion cracking (SCC) of an Al-6.13 wt%Zn-2.10wt%Mg alloy were investigated by the Weibull's distribution method. Specimens were solutlon treated at 460°C for 1h, quenched into ice-water and aged at 120°C for 24h. The SCC test was performed at 33°C in 3.3%NaCl+0.2%H₂O₂ aqueous solution of pH 5.2 under controlled potential. The constant stress of 60% of the yield stress was applied. All the shape parameters (m) were larger than 1 indicating the wearing-out failure. The shape parameters for t_f and t_i decreased under the nobler potential than the rest one, while the shape parameters for t_f, t_i and t_c increased under the lower potential than the rest. The life time, η for t_f and t_i decreased under the nobler potential than the rest and increased under the lower potential than the rest. The life time for t_c was shorter than the half for t_i. The major part of the life time for t_f was that for t_i. This implies that the life time for t_f depends on that for t_i. The probability density function f(t) which corresponded to the actual failure was determined from the values of m and μ.