Dynamic precipitation and enhanced mechanical properties of ZK60 magnesium alloy achieved by low temperature extrusion

Abstract

In this study, dynamic precipitation was observed in ZK60 (Mg-6.0Zn-0.5Zr) alloy during low temperature extrusion. The microstructure and mechanical properties of the alloy were investigated for various extrusion temperatures (400 oC, 350 oC and 300 oC). Decreasing extrusion temperature resulted in an increased dynamic precipitation as well as grain refinement. With decreasing extrusion temperature from 400 oC to 300 oC, the grain size was refined from 9.6 μm to 1.4 μm, and the dynamic recrystallization was changed from a discontinuous mechanism to a continuous one. The low temperature extrusion (300oC) resulted in an increased defect density and a supersaturated Zn in Mg matrix, which promoted the nucleation and potential for precipitation during extrusion process. The dynamic precipitates accelerated the nucleation of new grains during the dynamic recrystallization process. Besides the grain size, the texture intensity was also reduced. Due to the grain refinement and texture weakening during low temperature extrusion, both the mechanical strength and tensile ductility were improved with decreasing extrusion temperature. When extruded at 300 oC, the ZK60 alloy achieved a relatively high tensile yield strength (TYS) of 295 MPa and a remarkably high tensile elongation of 27.7%.