Abstract
To reveal the relationship between grain size and twinning deformation of magnesium alloys under cyclic strain, this study carried out a group of strain-controlled low-cycle fatigue experiments and statistical analysis of microstructures. Experimental results show that the shape of the hysteresis loop exhibits significant asymmetry at different strain amplitudes, and the accumulation of residual twins plays an important role in subsequent cyclic deformation. For the different strain amplitudes, the statistical distribution of the grain size of magnesium alloy approximately follows the Weibull probability function distribution, while the statistical distribution of twin thickness is closer to that of Gaussian probability function. The twin nucleation number (TNN) increases with the increase of grain size, but there is no obvious function relationship between twin thickness and grain size. Twin volume fraction (TVF) increases with the increase of grain size, which is mainly due to the increase of TNN. This work can provide experimental evidence for a more accurate description of the twinning deformation mechanism.
Highlights
The component of Magnesium alloy is often subject to cyclic loading in service
Since twin thickening is not sensitive to the grain size according to the results shown Figure 9, the increase of Twin volume fraction (TVF) is mainly reflected by the increase of twin nucleation number (TNN)
This study carried out tests of symmetric cyclic tension-compression loading under strain control at six different strain amplitudes on AZ31 magnesium alloy, made a statistical analysis of microstructures such as grain size, twinning deformation and so on, analyzed the relationship between macroscopic cyclic hysteresis loop curve of magnesium alloy and twinning deformation, made further statistical investigation into the relationship between grain size and the distribution of twins and obtained the following conclusions: 1
Summary
Many experiments show that the evolution of the stress-strain curve, yield strength and hardening rate of magnesium alloy varies significantly with different loading paths [1,2,3,4]. Magnesium alloy presents strong Bauschinger-effect and remarkable asymmetric plastic flow behavior during strain-controlled cyclic tension-compression tests [5,6]. In the majority of symmetric strain-controlled fatigue tests of Magnesium alloy [7,8], dislocation slip and twinning-detwinning deformation are two important patterns of plastic deformation. Dislocation slip acts as the main mechanism of plastic deformation when the applied strain amplitude is relatively small, while twinning-detwinning deformation plays a predominant role during cyclic deformation at high strain amplitudes. Twinning deformation lacks sensitivity to temperature and strain rate effects. The high critical resolved shear stress (CRSS) is the main factor for crystal
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