Al-Zn-Mg合金の応力腐食割れに関する研究-1-

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Al-5.3wt. %Zn-1.4wt.%Mg alloy specimens were heated by three conditions of aging (1) at 120℃ for 2 days, (2) at lOO℃ for 3 days and (3) 80℃ for 4 days after quenching into water at 0℃, after solidification at 460℃ for an hour. Nineteen test pieces on each aging condition were tested under the constant applied stress (80% or 60% of the yield stress, σy) in 3.5% NaCl+0.2% H202 solution of pH 4.0. Crack initiation time (ti), crack propagation time (tc) and failure time (tf) were measured and plotted on the Weibull's probability paper which is widely used in reliability engineering. Probability distributions of failure time (tf=ti+tc) were found to be described as the single Weibull's distributions. The shape parameter (m) of the Weibull's distribution of failure time was found to be nearly unity (m≒1) at applied stress of 80% of the yield stress, and larger than unity (m＞1) at applied stress of 60% of the yield stress, on each aging condition. Other parameters of the Weibull's distribution which are the location parameter (γ) and the scale parameter (α) were calculated. And then, the cumulative failure distribution function F(t), failure probability density function f(t) and failure rate λ(t) vs time curves, and the calculated frequency (fc) were described on the histogram of each condition. By microscopic observations, the crack propagations by stress corrosion cracking of the alloy seemed to be the type of intergranular cracking in all conditions.
奈良教育大学の論文

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岡敏博
奈良教育大学技術教室

Al-Zn-Mg合金の応力腐食割れに関する研究-1-

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