DSC and TEM analysis of lattice defects governing the mechanical properties of an ECAP-processed magnesium alloy

The mechanical properties of the Mg alloy AM60 can be improved significantly by severe plastic deformation (SPD). The lower the temperature (down to 150 °C) of equal channel angular pressing (ECAP) the higher is the resulting strength (up to 310 MPa) which can be ascribed to the concomitant decrease of grain size (down to 1 ?m). After ECAP-processing at temperatures 150¿210 °C the ductility remains at about the same high level (?15%) as in the initial material. This is explained with the presence of Al12Mg17 precipitates with a size of about 500 nm, which decrease the remaining concentration of Al in the solid solution of the matrix. Differential scanning calorimetry (DSC) revealed four peaks during heating runs. The most remarkable peak occurs at 390 °C in the initial sample, and at 360 °C in the material ECAPed at 150 °C. Transmission electron microscopy (TEM) analyses showed that this peak can be associated with the dissolution of the Al12Mg17 precipitates as well as with the annealing of dislocations and possibly vacancy clusters, and that ECAP has the potential to induce a shift of a phase boundary to lower temperatures because of ECAP induced lattice defects.