Al-8%Mg合金の応力腐食割れに及ぼす水素の影響

抄録

The mechanism for stress corrosion in the Al-Mg alloy is investigated. Charged hydrogen has an influence to the susceptibility to stress corrosion and lowers the life. The upper and lower critical concentrations are found. Increase in the susceptibility is saturated beyond the former at the amount of hydrogen increase 0.35 cc/100g and the susceptibility is unchanged below the latter at 0.15 cc/100g. The amount of hydrogen absorbed in the alloy exceeds the latter even in the normal stress corrosion condition. The stress corrosion cracking proceeds through the following stages. i) Electrochemical pitting ii) A strong acid atmosphere constituted near the bottom of the pitts by impediment in fluidity of corrosive mediums leads to a continuous reaction accompanying hydrogen generation iii) A part of generated hydrogen absorbed and concentrated in grain boundaries results in formation of embrittle paths iv) Cracks nucreate when a concentrated stress exceeds a fracture strength of embrittled region, and stop by stress relaxation caused by crack opening or by reaching to an unembrittled region. And v) the stages above mentioned are repeated.