Alireza Ghaderi

Deformation modes and anisotropy in magnesium alloy AZ31

Abstract A strongly textured sheet of magnesium alloy AZ31 has been subjected to tensile testing at temperatures between ambient and 300 °C. Structures have been examined by optical and transmission electron microscopy and also by atomic force microscopy to quantify surface displacements seen at grain boundaries. Plastic anisotropy varies strongly with test temperature as was observed previously by Agnew and Duygulu. The present findings do not support the view that crystallographic becomes a major contributor to deformation at higher temperatures. Rather, the material behaviour reflects an increasing contribution from grain boundary sliding despite the relatively high strain rate (10– 3 s– 1) used in the mechanical tests.

Microstructure and texture development in Ti-5Al-5Mo- 5V-3Cr alloy during cold rolling and annealing

This study focuses on the microstructure and texture evolution of a Ti-5Al-5Mo-5V-3Cr alloy during cold rolling and annealing treatments. Three samples with different initial microstructures were cold rolled to a 40% reduction in thickness. The starting microstructure of one sample was single β phase while two other specimens were α+β phases with different α particle sizes, distributed in β grains. For all three samples, the average size of primary β grains was 150 µm. The cold rolled specimens were then annealed at 860 °C (10 °C above the β transus temperature) for 5 minutes followed by water quenching. Microstructure development during cold rolling and recrystallization was studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) technique. Microstructure investigations showed that massive amount of shear bands occurred during the cold rolling of the single β phase sample while only a few shear bands were observed in the α+β cold rolled microstructures. The cold rolled texture of the sample comprised of a single β phase contains a gamma fibre (//ND) and a partial alpha fibre (//RD). Annealing treatment decreased the intensity of the cold rolled texture in the single β phase sample. Also, it was found that the presence of α precipitates changes the common annealing texture observed in the single β phase specimen.

The Effect of Ageing on the Compressive Deformation of Mg-Sn-Zn-Na Alloy

The influence of ageing on deformation twinning in an extruded Mg-6Sn-3Zn-0.04Na alloy is investigated. In-situ compression tests have been carried out using high resolution synchrotron X-Ray Diffraction (XRD) to measure the influence of precipitates on twining activity. Synchrotron experiments revealed the increase in the critical resolved shear stress of twinning with ageing. The compressive yield strength (along the extrusion direction) of the aged sample increased by ~150% over the non-aged specimen. To obtain statistical insight into the twinning activity, the microstructure of the non-aged and aged samples (200°C, 24 hours) deformed up to ~1% plastic strain was studied using optical microscopy. A higher number of thinner twins were observed in the microstructure of the aged sample compared to the non- aged sample.