Abstract
Corrosion cracking or season cracking occurs in the Al-Mg base alloys containing more than 5%Mg when exposed to tensile stress and a certain environment. An extensive study was undertaken to develope an aluminum alloy resistant to stress corrosion cracking. The effect of additions of 0.3%Cu and 0.2%Zr in Al-6∼9%Mg alloys on stress corrosion cracking has been investigated in 3.5%NaCl solution at room temperature under conditions of constant load and constant deflection.
The lowest stress causing corrosion cracking i.e. “threshold stress” is less than 3 kg/mm2 (corresponds to 23% of the 0.2% proof stress) for Al-8%Mg alloy quenched from 400°C and aged at 130°C for 7 days. Small additions of Cu, Zr and especially both elements improve the resistance to stress corrosion cracking of Al-Mg alloys. For Al-8%Mg-0.3%Cu-0.2%Zr alloy the “threshold stress” is 10 kg/mm and it is increased up to 15 kg/mm2 (corresponds to 83% of the 0.2% proof stress) when the alloy was air-cooled from the solution temperature.
Mechanisms of these effects are discussed on the basis of the direct observation of precipitates in grain boundaries and the measurements of electrical resistivity.
