Effect of precipitation in the compressive behavior of high strength Mg-Gd-Y-Zn extruded alloy


The influence of β′ and γ' precipitates on prismatic and basal planes and long-period stacking ordered (LPSO) fibers on the compressive behavior of high strength Mg-Gd-Y-Zn alloy was investigated using the combination of in-situ synchrotron radiation diffraction and acoustic emission, as well as transmission electron microscopy. After extrusion, the microstructure is characterized by highly oriented LPSO fibers elongated along the extrusion direction within the magnesium matrix. The microstructure of the magnesium matrix consists of a mixture of randomly oriented DRX-ed and coarse, textured non-DRXed grains (DRXed means Dynamically Recrystallised). Alloying elements in solid solution in the as-extruded condition precipitate during heat treatment at 200 °C. The formation of β′ prismatic plates and γ′ basal lamellar precipitates increases the compressive yield stress from 310 to 409 MPa. The onset of macroscopic plastic deformation in as-extruded and peak aged conditions is controlled by the activation of extension twinning in non-DRXed grains. In the peak aged alloy, prismatic plates and basal lamellae interact with twins during the propagation and growth stages of these. β′ precipitates are more efficient than γ′ basal lamellae not only in hindering extension twinning but also in the hardening of the basal system. During twin growth, the internal stress in the β’ precipitates continuously increases due to stress misfit generated when precipitates are engulfed by twins.
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