Effect of electric current on recrystallization kinetics in interstitial free steel and AZ31 magnesium alloy

The effect of electric current on recrystallization kinetics in interstitial free (IF) steel and AZ31 magnesium alloy was investigated based on Vickers hardness measurements and microstructural observation. Electropulsing treatment (EPT) and furnace heat treatment (HT) for these work-hardened metals were carried out under various temperature and time conditions. The Vickers hardness value after EPT was clearly lower than that after HT at the same annealing condition in both IF steel and AZ31 alloy. The microstructural observation confirms that the reduced hardness value was caused by recrystallization. This implies that the recrystallization kinetics was accelerated by the athermal effect distinct from Joule heating. To identify the athermal effect of the electric current on the recrystallization kinetics, the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation was adopted. In both IF steel and AZ31 alloy, the value of the Avrami exponent, which depends on the nucleation rate in recrystallization, was higher in EPT than in HT. In addition, it was observed that the activation energy for recrystallization was reduced in EPT.