Extrusion and precipitation hardening behavior of AZ91 magnesium alloy
(Department of Metallurgical and Materials Engineering,National Institute of Technology, Tiruchirappalli 620 015, India)
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