Effect of temperature on the hot deformation behavior of AZ80 magnesium alloy

Abstract

The present research studies the hot forgeability of a cast AZ80 alloy by means of uniaxial compression tests using a Gleeble® 3500 thermal-mechanical simulator. Compression tests were conducted for temperatures ranging from 300 °C to 450 °C, and constant true strain rates ranging from 0.001 s−1 to 1 s−1, while the characterization of deformed samples for microstructure and texture was performed only for the samples deformed within 300 °C–400 °C, at a strain rate of 0.001 s−1. The samples were deformed to true strains of 0.05, 0.15, 0.4 and 1.0, to study the microstructure and texture evolution with deformation strain, while the characterization was performed using optical microscopy, SEM-EDX, and EBSD. Analysis of the flow stress data suggested a transition in the rate controlling deformation mechanism from dislocation cross-slip at 300 °C to dislocation climb at 400 °C, with a corresponding transition in the dominant DRX mechanism from continuous dynamic recrystallization (CDRX) to discontinuous dynamic recrystallization (DDRX). The thermodynamic stability of the Mg17Al12 phase (which is the dominant secondary phase in the AZ80 alloy) varied over the test temperature range, and significantly impacted the microstructure and texture evolution at different test temperatures. At 300 °C, multiple morphologies of the Mg17Al12 precipitates were present in the microstructure during deformation, and affected the DRX behavior of the material differently. At 400 °C, the precipitates rapidly dissolved in the α-Mg matrix, while the DRX took place by the grain boundary bulging mechanism, with the newly formed DRXed grains preserving the deformation texture. The study shows that the effect of temperature on the hot deformation behavior of the AZ80 alloy is especially pronounced due to a changing amount of the Mg17Al12 phase in the microstructure.