Microstructural evolution in ZK60 magnesium alloy during severe plastic deformation

A ZK60 alloy was subjected to severe plastic deformation by torsion straining under high pressure at ambient temperature. The data of microhardness, measurements, X-ray analysis and TEM observation showed that intense plastic straining resulted in formation of nanometerscale structure characterized by presence of high internal stress fields. The effect of phase composition of the magnesium alloy on the formation of ultrafine grain structure was examined. It was shown that prior aging promoted the formation of fully grained structure during severe plastic deformation, At the same time. the size of new grains formed was found to be smaller in the quenched state of the magnesium alloy than in the aged state. Grain formation during intense plastic straining was interpreted in terms of low temperature dynamic recrystallization. The mechanisms of ultrafine grain structure formation in hcp material during severe plastic deformation and the role of non-basal slip in this process are discussed.