Effect of extrusion temperature on the microstructure and mechanical properties of Mg97Y2Zn1 alloy

The influence of extrusion temperature on microstructure and mechanical properties of Mg97Y2Zn alloy have been investigated. The one-step extrusion and the two-step extrusion were conducted at the different temperatures. It was found that the extrusion temperature not only influence the microstructure of Mg97Y2Zn1 alloy but also its mechanical properties. The microstructure of the Mg97Y2Zn1 alloy processed by the one-step extrusion at 673K is non-uniform. Coarse grains elongated along the extrusion direction coexisted with small volume fraction of fine dynamic recrystallization (DRX) grains formed around secondary phase and in the vicinity of the distorted original grain boundaries. After the two-step extrusion at different temperature from 623K to 773K, the DRX process of Mg97Y2Zn1 alloy is completed and the uniform equiaxed grains were obtained. The final grain size increases with increasing deformation temperature. The alloy processed by first step extrusion exhibits highest strength by lowest elongation. After the second step extrusion, however, the strength is decreased and elongation is increased. During the second step extrusion at 623K, twins are observed at the beginning of the extrusion. The small recrystallized grains appeared along some original grain boundary areas and twinned regions. With increasing strain, the volume fraction of recrystallized grains increases progressively. However, there is no twin occurs observed at the beginning of the second step extrusion at 773K. Instead, some uniform equiaxed recrystallized grains can be observed. The small recrystallized grains appeared along some original grain boundary areas. With increasing strain, the volume fraction of recrystallized grains increases progressively and the grain size is increasing too. It seems that the DRX was brought forward at higher extrusion temperature.