Nondestructive tests on the effect of Mg content on the corrosion and mechanical properties of 5000 series aluminum alloys

Using the nondestructive testing techniques conductivity measurement and ultrasonic testing, we explored the importance of the effect of Mg content (3–6 wt%) on the corrosion and mechanical properties of 5000 series chill-rolled Al–Mg alloys. The results indicate that all of alloys showed no β-phase precipitation before sensitization and that their conductivity and sound wave velocity decreased with increasing Mg content. After sensitization of the alloys, their grain boundaries showed significant β-phase precipitation and corrosion. The alloy conductivity and sound wave velocity increased with the increase in Mg content. Precipitates became more obvious and continuous, and the change in rate of conductivity was greater, while the change in rate of sound wave velocity had a less-significant trend. Addition of Mg atoms not only increased the strengthening effect on the solid solution of Al–Mg alloys, but it also reduced the stacking-fault energy of the alloys. During tensile deformation, the alloys exhibited high work-hardening rate, effectively suppressing the occurrence of necking. Thus, when the Mg content was higher, the strength and elongation of the alloy increased. In contrast, the strength of sensitized high-Mg alloys declined within a larger range. The conductivity, sound wave velocity, corrosion properties, and mechanical properties were linearly correlated. We thus demonstrated that nondestructive testing techniques can be effective methods for evaluating the effect of Mg content on the corrosion and mechanical properties of chill-rolled Al–Mg alloys. Moreover, the conductivity measurement was more sensitive than was ultrasonic testing in detecting precipitation of the strengthening phase.