Effect of pre-compression on microstructural evolution, mechanical property and strengthening mechanism of AZ31 alloy

The effect of pre-compression deformation on the microstructural evolution, mechanical property and deformation behavior of AZ31 magnesium alloy was studied. The alloy was microstructurally characterized with a combination of optical microscopy, electron backscatter diffraction, X-ray diffraction and energy-dispersive spectrometer. The results indicate that average number of twins per grain and dislocation density increases with an increase in compressive pre-deformation level. Stress–strain curves of low pre-strained samples (0%, 1% and 3%) present concave-up features, whereas concave-down shapes are detected for high pre-strained samples (6% and 8%) in uniaxial compression tests. The corresponding underlying deformation mechanism transists from a twin-dominated mechanism to a slip-dominated mechanism. This deformation mechanism transition is related to {10–12} twinning, which leads to grain refinement and crystal orientation change, as well as increased dislocation density. The yield strength linearly increases with increasing equivalent grain size regardless of the deformation mechanisms. Quantitative analysis reveals that the contributions from texture strengthening, twinning/grain boundary strengthening and dislocation strengthening increase as pre-compression level increases. Texture strengthening is the dominant strengthening mechanism for high pre-strained samples.