Patrik Dobroň

Acoustic emission study of the mechanical anisotropy of the extruded AZ31 alloy

Abstract The mechanical anisotropy behaviour of the extruded AZ31 magnesium alloy was investigated by in-situ measurements of acoustic emission. Specimens taken in the extrusion direction were uniaxially loaded in tension and compression at room temperature. The acoustic emission count rates were correlated with stress – strain curves and their values show local maxima at the yield point, which is linked with cooperative dislocation processes and/or with the occurrence of deformation twins, especially in compression tests. During compression tests, another acoustic emission maximum occurs after the yield point which indicates the activation of further deformation mechanisms. In this paper the acoustic emission results are presented and discussed in terms of texture evolution during plastic deformation.

Acoustic emission study of the deformation behaviour of magnesium sheets

Abstract In this study, acoustic emission (AE) measurements were performed during tensile testing of sheets of four magnesium alloys in different orientations with respect to the tensile axis in order to investigate the influence of microstructure and texture on the deformation behaviour. AE measurements could especially be used for analysing the activity of twinning. It was shown that the grain size has an important impact on the AE count rates which was directly related to the activity of deformation mechanisms. Small changes in the texture can significantly affect the activity of twins. It was further shown that a weak texture promotes ductility.

Effect of Thermo-mechanical Treatment of Extruded Z1 Mg Alloy on Resulting Mechanical Properties

The formability and mechanical properties of Mg alloys are strongly influenced by a formation and growth of twins. The contribution of twinning to plastic deformation can be modified by initial texture, introducing solute segregation and precipitation at the twin boundaries. The interaction of solute atoms and precipitates with grain and twin boundaries during thermo-mechanical treatment and their effect on mechanical properties will be discussed in term of acoustic emission (AE). An AE signal, recorded during deformation tests, can provide information about active deformation mechanisms during plastic deformation with respect to the microstructure and texture as well as to solute segregation and precipitates along dislocations, grain and twin boundaries. The microstructure development of the extruded Z1 Mg alloy prior and after pre-treatment as well as after subsequent loading will be investigated by scanning electron microscopy (SEM) including electron backscattered diffraction (EBSD) technique.

Effect of Extrusion Ratio on Microstructure and Resulting Mechanical Properties of Mg Alloys with LPSO Phase

The WZ21 (Mg + 1.8 wt% Y + 0.7 wt% Zn) magnesium alloy having an addition of 0.5 wt% of CaO was extruded with different extrusion ratios (4:1, 10:1, 18:1) at 350 °C. In all alloys, a long-period stacking-ordered (LPSO) phase composed of Zn and Y is formed. The microstructure was analyzed by electron backscatter diffraction (EBSD) mapping. The WZ21 alloy after extrusion with the extrusion ratio of 4:1 contains large grains. The fraction of recrystallized grains increases with increasing extrusion ratio. All samples have basal planes oriented parallel to the extrusion direction (ED) and this texture weaken with increasing extrusion ratio. Mechanical properties of the samples were investigated during compression along ED at room temperature and at a constant strain rate of 10−3 s−1. Concurrently, with the deformation tests, the acoustic emission (AE) response of the specimens was recorded. The maximum of the AE count rate in all cases corresponds to the macroscopic yield point.

Thermo-Mechanical Treatment of Extruded Mg–1Zn Alloy: Cluster Analysis of AE Signals

The proper thermo-mechanical treatment can improve mechanical properties of extruded Mg alloys through a solute segregation and precipitation along twin boundaries. The effect of heat treatment on mobility of twin boundaries with respect to applied loading direction was studied in extruded Mg–1Zn alloy using the acoustic emission (AE) technique. The adaptive sequential k-means clustering (ASKC) was applied to analyze the AE data in order to determine the dominant deformation mechanism in a given time period. The AE energy, median frequency and the number of elements in individual AE clusters are the main parameters of presented clustering analysis. Active deformation mechanisms are discussed with respect to mutual orientation of grains and loading direction.

Mechanical Properties of Thermo-Mechanically Treated Extruded Mg–Zn-Based Alloys

Mechanical properties of extruded Mg alloys are significantly influenced by the activation of extension twins during compression along the extrusion direction (ED) because of a strong texture with basal planes oriented parallel to ED. At the same time, the heat treatment is also supposed to tune mechanical properties via strengthening or softening mechanism. The influence of heat treatment on the mechanical behavior of Mg–Zn-based alloys with an addition of Ca and Nd in as-extruded state and after pre-compression (i.e. partly twinned microstructure) is discussed in the paper. Difference in distribution of precipitates for two materials after applying heat treatment at 200 °C for 16 h was observed. Isothermal ageing of pre-strained samples leads to strengthening in ZN10 alloy and softening in ZX10 alloy.

Acoustic Emission Study of High Temperature Deformation of Mg–Zn–Y Alloys with LPSO Phase

Magnesium alloys with different content of zinc (Zn) and yttrium (Y) were extruded at an extrusion ratio of 18:1 at 350 °C. The alloying elements in both Mg alloys formed a long period stacking ordered (LPSO) phase, which during the extrusion process was elongated along the extrusion direction (ED). The magnesium matrix has bimodal character composed by fine dynamically recrystallized (DRX-ed) grains and initial coarse grains elongated along ED. Compression tests with concurrent acoustic emission (AE) measurements were performed along ED at 200, 300, and 400 °C. The deformation mechanisms and the mechanical properties at 200 °C are very similar to those obtained at ambient temperatures, i.e. in the alloy with low volume fraction of the LPSO phase (<10%) twinning controls the yielding, while in the alloy with high volume fraction of the LPSO phase (around 35%) dislocation slip and kink formation are dominant. At 300 °C the reinforcing effect of the LPSO phase is reduced and at 400 °C it is not effective anymore.

An Acoustic Emission Study of Deformation Behavior of Wrought Mg Alloys

The influence of the pre-compression level on subsequent tensile deformation behavior has been investigated for two extruded Mg alloys with a different grain size distribution. The Mg–Zn–R are earth alloy has homogeneous microstructure, while the Mg–Al–Zn alloy exhibits bimodal microstructure. Deformation tests were performed at room temperature and at a constant strain rate of 10−3 s−1. Three pre-compression stress levels were chosen to receive microstructure containing a low number of twins, partially and fully twinned grains, respectively. The concurrent acoustic emission (AE) measurement provides real time information about collective dislocation motion and twin nucleation. Active deformation mechanisms during tensile loading are discussed in term of the AE response.

In Situ Investigation of Deformation Mechanisms in Mg–Zn–Y Magnesium Alloy with LPSO Phase by Diffraction Methods and Acoustic Emission

The influence of the LPSO (long-period stacking ordered) phase orientation and the microstructure of the magnesium matrix on the deformation mechanisms of Mg–Zn–Y magnesium alloy has been investigated by diffraction methods and acoustic emission (AE) measurements. The adaptive sequential k-means analysis (ASK) method, offering identification of the dominant deformation process (basal, non-basal slip, twinning, kinking) in a given time period, has been used for AE data evaluation. The results indicate that the kinking mechanism, twinning and activation of non-basal slip exhibit a significant dependence on the initial texture and the orientation of the LPSO phase with respect to the loading axis.

Evolution of AC conductivity of wet illitic clay during drying

The evolution of the AC electrical conductivity during drying as well as the relationship between sample volume and moisture of green illite samples were investigated. The samples were prepared from illitic clay (80 mass % illite, 4 mass % montmorillonite, 12 mass % quartz and 4 mass % of orthoclase) and distilled water with initial moisture content 36 mass % and were freely dried in air. Conductivity was measured by the volt-ampere method with AC power supply of 5 V in the frequency range from 50 Hz to 10 kHz. The AC conductivity steeply increased with increasing moisture, up to 15 mass %. At higher values of the moisture, the AC conductivity was high and almost constant. The volume of samples increased with increasing moisture when the moisture was higher than 8 mass %. Below this value, the dimensions of samples do not significantly change. The dependence of the relative volume change on moisture is presented in a form of the Bigots curve.