Abstract:The as-cast AZ91 magnesium alloy was extruded at 250 °C, 300 °C and 350 °C, respectively with extrusion ratio of 4:1 followed by precipitation hardening treatment (T6). The coarse and segregated Mg₁₇Al₁₂ intermetallic precipitate in AZ91 magnesium alloy was refined and distributed uniformly in α-magnesium matrix by direct hot extrusion combined with precipitation hardening treatment. The dynamic recrystallization phenomenon, partial to full, was observed in this alloy with respect to the extrusion temperature. Ultimate tensile strength of this alloy is increased from 190 MPa (as cast) to 570 MPa after extrusion. The age hardening characteristics of AZ91 magnesium alloy is more dependent on the grain size. The peak hardnesses are obtained in the aging time of 35, 30 and 20 h for alloys extruded with ratio of 4:1 at three different temperatures. Uniform and fine precipitates of Mg₁₇Al₁₂ in AZ91 Mg matrix were confirmed by scanning electron microscope (SEM).

Key words: AZ91 magnesium alloy; Mg₁₇Al₁₂ precipitate; extrusion; precipitation hardening