Effects of equal channel angular extrusion on the microstructure and high-temperature mechanical properties of ZA85 magnesium alloy

Abstract

This study examined the microstructure and high-temperature tensile properties of the Mg-8wt.%Zn-5 wt.%Al (ZA85) alloy that was subjected to equal channel angular extrusion (ECAE) with various passes at 180-250 degrees C. The original grain size and precipitate size of the as-cast specimen were 150 and 100 mu m, respectively. The average grain size was reduced to 4 mu m by dynamic recrystallization and the precipitate size was reduced to 1 mu m after six ECAE passes at 180 degrees C. However, the average grain size of the ECAE-processed specimens at 250 degrees C increased from 14 mu m after two passes to 20 mu m after four passes owing to the grain growth effect. In tensile tests at 200 degrees C, the ultimate tensile strength (UTS) and yield strength (YS) of the specimens processed with six ECAE passes at 180 degrees C improved to 249 MPa and 162 MPa, respectively, compared with 105 MPa (UTS) and 74 MPa (YS) for the as-cast specimens. Furthermore, elongation increased from 5.1% to 28.5%. This significant improvement in the high-temperature tensile properties of the ZA85 alloy was attributed to the refined grains and the well-distributed fine Mg-32(Al, Zn)(49) (tau-phase) precipitates. (C) 2012 Elsevier B.V. All rights reserved.