MICROSTRUCTURE AND MECHANIAL PROPERTIES OF AS-EXTRUDED Mg-Sn-Al-Zn ALLOYS

Mg-(9-x)Sn-xAl-lZn (x=1, 2, 3 and 4 wt.%) alloys were subjected to indirect extrusion, and the microstructure and mechanical properties of these as-extruded Mg-Sn-Al-Zn (TAZ) alloys were investigated. The TAZ alloys contain only fine Mg2Sn second-phase particles in the a -Mg matrix, and the amount of precipitates increase with increasing Sn contents. In addition, the TAZ 811 alloy shows finer grain structure than the TAZ 541 alloy due to a larger amount of Mg2Sn particles, which act as nucleation sites for recrystallization and/or prevention of grain growth by the pinning effect. The textures of the alloys show a typical basal pole orientation and an unusual <11-20> component in which one axis of the HCP unit cell is parallel to the extrusion axis. Tensile yield strength increases with Sn content, while ultimate tensile strength is almost identical due to the increased strain hardenability with Al content. The tension-compression yield asymmetry decreases with reducing Sn content, which is mainly due to the decrease in the amount of particles promoting twin nucleation.