Plastic instability of Al-Mg alloys during stress rate change test

Plastic instability or Portevin-Le Châtelier effect is observed during stress rate change test of Al-Mg alloys 5005O and 5052O at room temperature. In the stress rate change experiments, strain retardation and plastic instability are observed, that is, although the applied stress rate changes, plastic strain is insignificant until the plastic instability occurs. The occurrence of plastic instability is related to the applied stress rate and retention time before the applied stress rate change. For the fixed final stress level, the faster of stress rate change, the more significant instability of plastic deformation is; also at the same stress rate, the longer the retention time, the higher the relative stress value of initial instability is. Compared with the same test condition of both 5005 and 5052 alloys, the latter one shows more energy needed in the occurrence of plastic instability due to higher magnesium content. By the argument of dynamic strain ageing effect, plastic instability during stress rate change test could be justified as the interactions between solid solution element, magnesium, and dislocations.