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In situ diffraction analysis using high energy synchrotron radiation to investigate the influence of active deformation and recrystallisation mechanisms on the microstructural development of new magnesium sheet alloys

Subject Area Metallurgical, Thermal and Thermomechanical Treatment of Materials
Mechanical Properties of Metallic Materials and their Microstructural Origins
Term from 2015 to 2019
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 262840495
 
Final Report Year 2019

Final Report Abstract

The main aim of the project was to understand the influence of deformation and recrystallization mechanisms in rare-earth or calcium and combination with Zn alloyed Mg, compared to the single addition of Zn alloys. We revealed that the addition of Nd or Ca to pure Mg leads to a higher activation of prismatic dislocation slip, which acts as a main deformation mechanism under tensile loading in comparison with to binary Mg-Zn alloys. Concurrently, a retardation of the recrystallization behavior, i.e. delayed relaxation of dislocation densities is revealed. In succession, the higher activation of the prismatic dislocation leads to texture development, i.e., a spread basal pole perpendicular to the LD. The former is enhanced in combination with the addition Zn, i.e. ZN10 and ZX10. In order to reveal the abovementioned finding, the microstructure and texture developments were investigated at different levels of deformation in same volume area by the diffraction peak profiles using the synchrotron X-ray radiation, consequently, by in-grain misorientation analysis using the scanning electron microscopy and by texture simulations using a (e)VPSC model. The project started with observation of texture development in different Mg alloys, containing rare-earth and calcium, and their ternary alloys combined with Zn. Comparison was carried out to the binary Mg- Zn alloys (modified with Zr for grain refinement) in this study as an example for a conventional Mg alloy, which develops a strong basal texture. All examined alloys were hot-rolled and annealed with different conditions in order to minimize the influence of the grain sizes and to avoid statistic issue for the in-situ diffraction experiments during tensile loading. Using these different Mg alloy sheets having different initial textures, the experimental investigations of the activated dislocation slip systems as well as the recrystallization behaviors as aspect with the addition of alloying element at different temperatures were successfully carried out. The Nd or Ca containing Mg alloys showed approximately 150-200% increases of the nonbasal dislocations during tensile deformation, especially prismatic dislocations, compared to the Nd- and Ca-free counterpart, and the nonbasal dislocations in ternary alloys containing Zn and Nd or Ca increased approximately by 200-250%. Our experimental investigations showed that the activated prismatic slips by the addition of Nd or Ca leaded to a texture development which is broadened in the basal pole perpendicular to the LD during tensile deformation. Particularly the texture development was enhanced in combination of Zn and –Nd or –Ca due to the stronger activation of prismatic slips than other examined alloys. Furthermore, the Nd or Ca containing Mg alloys showed the retained activation of nonbasal dislocation density at elevated temperatures, while the free-Nd or –Ca containing Mg alloy showed the distinct relaxation of the dislocation densities accompanying the reduced activation of nonbasal - as well as - dislocations, i.e., the addition of Nd or Ca leaded to the change of recrystallization kinetics. This was clearly turned out as enhanced phenomenon in combination with Zn and Nd or Ca containing Mg alloys. The clear explanations on the higher activation of prismatic slips and change of recrystallization kinetics could not be determined in detail.

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