Al-Zn-Mg合金の応力腐食割れにおよぼす微量添加元素の影響について

Al-Mg-Zn合金の応力腐食割れの研究(第6報)

抄録

Stress corrosion cracking tests were performed on Al-4.5wt.%Zn-2.9wt.%Mg alloy and the same alloy containing an additional element of about 0.1at.% of any one of Cu, Cr, Ti and Zr. In addition, metallurgical parameters assumed to have effects on stress corrosion cracking sensitivity of the alloys were determined.
The results obtained were summarized as follows:
(1) There were no parameters having a close relationship to stress corrosion cracking sensitivity of the alloys. Though there were great differences in metallurgical properties between the alloy containing copper and the alloy containing any one of Cr, Ti and Zr, any of these elements improved stress corrosion resistance of the alloys. These phenomena made us to suppose that the stress corrosion cracking sensitivity of the alloys would be attributed to a complicated composition of many factors.
(2)Al-4.5wt%Zn-2.9wt.%Mg alloy aged at 90°C for 30hrs. had greater toughness and some of their properties were more sensitive to corrosion circumstances as compared with the alloy subjected to two-stepped aging. The alloy containing copper had poorer toughness and its decrease of strength in a corrosive agent was greater, but its corrosion resistance was higher. The properties of the alloy containing any one of Cr, Ti and Zr were nearly inverse to those of the alloy containing copper.