Al-Zn-Mg合金の応力腐食割れに関する研究-3-腐食電位の影響について

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To investigate the influence of corrosion potential on stress corrosion cracking (SCC) of A1-6.13wt.% Zn-2.10wt.% Mg alloy at five corrosion potentials with 150mV intervals from -1500 to -900mV vs Pt electrode, tensile tests under a constant load were carried out in 3.5 % NaCl + 0.2 % H202　aqueous solution of pH 5.4 at 33℃. Nineteen test-pieces at each potential were tested under the applied stress of 60% of the yield stress. Crack initiation time tj, crack propagation time tc and failure time tf were measured and plotted on the Weibull probability paper which is widely used in reliabillity engineering. The Weibull plots were analysed as the single Weibull distribution with both two parameters and three parameters. The shape parameter m and the mean value μ calculated from both Weibull distributions of tf, tj and tc were plotted as functions of the corrosion potential. The fracture surfaces of specimens were observed by Scanning Electron Microscope (SEM). The experimental results obtained were summarized as follows : (1) The higher the controlling potential as compared with the natural corrosion potential (-1200mV), the shorter the failure time of SCC. (2) The lower the controlling potential as compared with the natural corrosion potential, the longer the failure time of SCC. (3) The intergranular cracking occured with the hidrogen embrittlement by the pitting corrosion, the rupture of oxide film and the solution of η-phase precipitated along grain-boundaries. (4) The more the intergranular cracking were observed by SEM, the smaller the value of the Weibull distribution became. (5) The more the transgranular cracking were observed by SEM, the larger the value of shape parameter of the Weibull distribution became.
奈良教育大学の論文

著者

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-3-腐食電位の影響について

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