Microstructure evolution within adiabatic shear band in peak aged ZK60 magnesium alloy

Microstructure evolution in adiabatic shear band (ASB) in the peak aged ZK60 magnesium alloy cylindrical tube specimen after explosive radial compression was systematically investigated. High strain rate compression tests were performed by means of the radial collapse of thick-walled cylinder technique to achieve nominal strain rates of about 104 s(-1). The TEM results indicate that the elongated grains and deformed twins are the major characteristics in the boundary of the shear band. The central region in ASB was found to consists of ultrafme and equiaxed grains with a typical size of 100 nm. And it was found that precipitates within ASB were significantly reduced, namely the precipitates instantaneous dissolution during adiabatic shearing. It is proposed that fine equiaxed grains within ASB are the result of rotational dynamic recrystallization during localization. The free energy difference between the precipitates and matrix provided a thermodynamic condition for the dissolution of precipitates. Diffusion rate increased due to high strain rate, high shear stress (large strain) and adiabatic temperature rise, which caused instantaneous dissolution of precipitates.