M.G. Jiang

Microstructure and Mechanical Properties of an Extruded Mg-1.58Zn-0.52Gd Alloy

Mg-1.58Zn-0.52Gd (wt%) alloy was indirectly extruded at different temperatures and the resulting microstructure, texture and mechanical properties were investigated. The alloy extruded at 350 °C exhibited a typical bimodal microstructure, consisting of fine dynamically recrystallized (DRXed) grains of ~3.1 μm and coarse unDRXed grains elongated along the ED with many fine spherical Mg3Zn3Gd2 phase, and a strong \( \left[ {10\bar{1}0} \right] \) fiber texture, thereby resulting in high yield strength of 283 MPa and low elongation of 10.0%. With increasing extrusion temperature, the yield strength gradually decreased mainly due to increased DRXed grain size from the Hall-Petch relation, and the elongation increased due to the weakened extrusion texture and increased DRX fraction, suppressing crack initiation at twins in coarse unDRXed grains. As a result, the alloy extruded at 400 °C showed yield strength of 161 MPa and elongation of 24.7%.

Microstructure and Mechanical Properties of Mg–Zn–Gd Alloys After Rolling or Extrusion Processes

A series of Mg–Zn–Gd alloys were developed for large strain hot rolling, cold rolling and high-speed extrusion. The hot rolled Mg–2.0Zn–0.3Gd (wt%) alloys can be successfully rolled at 300 °C for a single pass reduction of 80% without any edge cracks, and the rolled sheet exhibited high yield strength of ~210 MPa and moderate elongation of ~22% due to fine grains and weak basal texture with broad angle distribution. The hot rolled Mg–2.0Zn–0.8Gd sheet showed excellent cold rollability due to the activation of {\( 10\bar{1}2 \)} extension twins and dislocation slips. Cold rolling could further modify the texture and enhance the strength. Besides, Mg–1.58Zn–0.52Gd alloy can be successfully extruded at high die-exit speed of 60 m/min without any surface defects in a wide temperature range due to the absence of thermally unstable eutectic phase and high solidus temperature. The high-speed extruded alloy showed high ductility of ~30%, which was twice than AZ31 alloy, because of the formation of rare earth texture.