Combination of in-situ diffraction experiments and acoustic emission testing to understand the compression behavior of Mg-Y-Zn alloys containing LPSO phase under different loading conditions

Abstract

The effect of the orientation of the non-recrystallized grains (non-DRX) and the LPSO phase on plasticity in extruded Mg97Y2Zn1 alloy with a bimodal grain structure have been studied in-situ using the combination of synchrotron diffraction and acoustic emission techniques during compression tests. The adaptive sequential k-means (ASK) procedure was applied to analyze the acoustic emission signal. This method can successful separate the signal for each possible deformation systems. Combining both techniques the deformation mechanisms that take place during the compression tests under different loading directions have been distinguish. Independently of the loading direction, the beginning of the macroscopic plasticity is always controlled by the activation of basal slip system in the DRX grains. However, highly oriented non-DRX grains and LPSO phase have a strong influence over the compressive deformation of the MgY2Zn1 alloy. The basal planes in the non-DRX grains were oriented parallel to the extrusion direction (ED). Thus, the activation of the extension twinning was found to be significant only in the ED mode. In the other two loading cases, TD and 45, the activation of non-basal slip systems has been detected. On the other hand, the reinforcing effect of the   1012 1011 2 elongated LPSO phase is the most effective, if the loading axis is aligned with the fiber direction (extrusion direction) since the load transfer mechanism is more effective. In this loading case, the LPSO can be plastically deformed due to kinking. This deformation mode has been isolated by the ASK procedure and characterized by in-situ scanning electron microscopy.

In-situ Investigation of the Microstructure Evolution in Long-Period-Stacking-Ordered (LPSO) Magnesium Alloys as a Function of the Temperature

“…The twin nucleation starts in the non-recrystallized grains and continues in small recrystallized one. Grain size dependence of twin nucleation studied by AE have been reported previously for Mg- (Dobron et al, 2011;Drozdenko et al, 2016) and Mg-LPSO alloys (Garcés et al, 2018). In case of S32 alloy deformed at RT, the maximum of AE count rate around 150 MPa (Figure 5A), whereas the lattice strain relaxation takes place in Mg phase grains above 300 MPa (Figure 6A).…”

“…The kinking at room temperature in S32 alloy is less developed, and it appears mostly in form of bended LPSO laths (cf. Figure 14 in Garcés et al, 2018). This can be hardly distinguished from the initial wavy form of the LPSO phase in the presented optical micrographs.…”

“…It was explained by the fact that the twin propagation is several order faster process than the twin growth (Vinogradov et al, 2016). At the same time, statistical analysis of AE signal in Mg-LPSO alloys has shown that kinking has similar characteristics to twinning (Garcés et al, 2018) and it can be also a source of burst high amplitudes AE events. Therefore, observed high amplitude burst AE events originate in twin nucleation and kinking.…”

“…All of them significantly depends both on materials parameters (volume fraction and orientation of the LPSO phase, the grain size of Mg matrix) and experimental conditions (loading direction, temperature etc.). There are numerous works investigating deformation mechanisms of such alloys at room temperature (e.g., Kishida et al, 2014;Garcés et al, 2018). Nevertheless, an in-depth understanding of deformation mechanisms (dislocation slip, kinking, and twinning) in Mg-LPSO based alloys as a function of temperature and volume fraction of the LPSO phase is still essential.…”

Anisotropic Plastic Behavior in an Extruded Long-Period Ordered Structure Mg90Y6.5Ni3.5 (at.%) Alloy

“…The LPSO phase with 18R or 14H structure shows a strong elastic and plastic anisotropy. In the elastic regime, the LPSO phase exhibits a higher Young's modulus and shear modulus compared to Mg [19][20][21][22] and depending on the LPSO crystal orientation. On the other hand, its plastic behavior is controlled by the activation of the basal slip system with a CRSS of around 10 MPa [23,24].…”