Ａｌ‐Ｚｎ‐Ｍｇ合金の応力腐食割れの統計学的研究

Abstract

Effects of aging on the failure time in stress corrosion cracking of Al-5.3Zn%-1.4wt%Mg alloy was studied by the Weibull distribution method. All test pieces were solution heat treated at 460°C for 1h and quenched into ice-water. Some of them were aged in three different ways, i) at 120°C for 2 days, ii) at 100°C for 3 days and iii) at 80°C for 4 days. The others were preaged at room temperature for a week and aged in the ways above mentioned. The test pieces were stress corrosion tested under constant applied stresses 80, 60 and 40% of the yield stress in 3.5%NaCl+0.2%H2O2 solution of pH4.0. The failure time obeys the single Weibull distribution with a location parameter. Shape parameters of Weibull distribution for the failure time are nearly unity under the applied stress 80% of the yield stress, but are larger than unity under those 60 and 40% of the yield stress. Aging temperature dependences of the mean and median failure times indicate that split aging prolongs the failure time. The longest failure time is achieved for the test pieces split aged at 120°C.