Time dependent springback of a magnesium alloy

• Springback of the bent AZ31 sheet continued for months at room temperature.
• Springback decreased dramatically in samples held in the bent state for months.
• Localized twin bands were observed in the compression zone of the bent samples.
• Detwinning occurred and contributed to the time dependent springback.
• The time dependent springback indicates creep occurred at room temperature.

A time dependent springback was observed in a Mg–Al–Zn (AZ31) rolled sheet after three-point bending at room temperature (RT). Two types of test were performed: (1) baseline springback – specimens were bent and immediately released and the springback was measured every month; (2) springback after holding – after bending, specimens were held in the bent state for up to five months, and the springback was measured after release. It was found that the springback increased nonlinearly with time in all the specimens. The springback dramatically decreased after being held for one month compared with specimens that were not held. The decline in springback increased as the holding time increased. These results indicate that creep and creep recovery occurred. Microstructure examinations revealed high density {101‾2}〈101‾1‾〉 twins in the compression zone of the bent specimens in the form of localized twin bands. After the specimens were unloaded, detwinning occurred and continued spontaneously over the five month time period, contributing to the observed time dependent springback.