Stress Corrosion Cracking and Corrosion Resistance of Mg–6%Al–1%Zn–2%Ca Extruded Magnesium Alloys

抄録

Stress corrosion cracking (SCC) and corrosion resistance of Mg–6 mass%Al–1 mass%Zn–2 mass%Ca (AZX612) extruded alloy were investigated by slow strain rate tensile tests (SSRT) in 0.01 M NaCl solution and immersion tests in 5 mass% NaCl solution, and compared with those of Mg–6 mass%Al–1 mass%Zn (AZ61) extruded alloy. In the SSRT in the salt solution, as-received AZX612 exhibited lower elongation and higher SCC susceptibility than those of as-received AZ61, indicating that calcium addition in Mg–Al alloy deteriorated SCC resistance. On the other hand, after solution treatment, improvement of elongation and SCC susceptibility occurred in both the alloys. Observation of surface profiles for AZX612 and AZ61 after the SSRT in salt solution revealed that corrosion pits on surface likely initiated SCC in both the alloys. The results of immersion tests showed the same tendency with those of SSRT in salt solution. It is suggested that SCC resistance of AZX612 and AZ61 was likely related to the microstructural change accompanied with calcium addition and solution treatment such as the change in distributions of Al₂Ca phase and Al-rich phase.