Microstructures and Tensile Properties of Hot-extruded Mg-6Zn-xCe (x=0, 0.6, 1.0, 2.0) Alloys

Abstract

Mg-6Zn-xCe (x = 0, 0.6, 1.0, 2.0) alloy ingots with diameter of 50 mm were extruded into bars with diameter of 12 mm at 300 °C. The microstructures were analyzed by X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy, and mechanical properties were tested at room temperature. The results showed that major intermetallic composition in as-cast Mg-6Zn and Mg-6Zn-0.6Ce alloys was Mg₄Zn₇ phase, during extrusion Mg₄Zn₇ phase was dissolved into matrix and then precipitated as MgZn₂. In as-cast and as-extruded Mg-6Zn-1Ce and Mg-6Zn-2Ce alloys the major intermetallic composition was T phase. The microstructure of as-extruded alloy was refined due to complete dynamic recrystallization, the average grain size decreased with increasing Ce content, which were 12.1, 11.7, 11.0 and 10.0 mm, respectively. High density MgZn₂ precipitated in Mg-6Zn and Mg-6Zn-0.6Ce alloys. The broken T phase particles were distributed linearly along extrusion direction. Mg-6Zn-0.6Ce alloy exhibited a high yield strength of 226.3 MPa that was about 24 MPa higher than Mg-6Zn alloy. However, with increasing Ce contents, the strengths were decreased slightly because the effects of precipitation strengthening of MgZn₂ and solid solute strengthening of Zn were weakened though the strengthening effect of T phase was enhanced.

Keywords

magnesium alloy / extrusion / microstructure / mechanical properties

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