Time Dependent Springback of a Magnesium Alloy

A time dependent springback was observed in a Mg-Al-Zn (AZ31) rolled sheet after three-point bending at room temperature (RT). The springback increased nonlinearly with time at RT. After bending, specimens were held in the bent state for up to five months, and 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 at RT. Microstructure examinations revealed that high density { 10\bar 12} < 10\bar 1\bar 1 > twins in the form of localized twin bands were present in the compression zone of the bent specimens. After the specimens were unloaded, detwinning occurred and continued spontaneously over the five month time period at RT, contributing to the observed time dependent springback.