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

摘要

This study examined the microstructure and high-temperature tensile properties of the Mg-8wt.%Zn-5wt.%Al (ZA85) alloy that was subjected to equal channel angular extrusion (ECAE) with various passes at 180-250 °C. The original grain size and precipitate size of the as-cast specimen were 150 and 100 μm, respectively. The average grain size was reduced to 4 μm by dynamic recrys-tallization and the precipitate size was reduced to 1 μm after six ECAE passes at 180 °C. However, the average grain size of the ECAE-processed specimens at 250 °C increased from 14 μm after two passes to 20 μm after four passes owing to the grain growth effect. In tensile tests at 200 °C, the ultimate tensile strength (UTS) and yield strength (YS) of the specimens processed with six ECAE passes at 180 °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) (T-phase) precipitates.