Sankara Sarma V. Tatiparti

Electrodeposition of Al-Mg Alloy Powders

Aluminum-magnesium alloys can potentially be used as hydrogen storage materials. In order to enhance the kinetics of hydrogenation, it is desirable to have agglomerates of fine powders with very small grain size. Electrodeposition is a viable method to produce pure powders with an ultrafine structure. In this paper we report the effect of magnesium content, electrolyte temperature, and current density on the characteristics of Al-Mg deposits produced galvanostatically using an organometallic-based electrolyte. The magnesium content of the deposits improved with increasing Mg concentration in the electrolyte, temperature, and current density. The results indicate that the morphology of the deposits is significantly affected by the magnesium content. Depending on the composition, the deposits consisted of face-centered cubic-Al(+Mg) and hexagonal close-packed-Mg(+Al) phases.

The Formation of Morphologies and Microstructures in Electrodeposited Nanocrystalline Al–Mg Alloy Powders

Al-Mg alloy powders were produced in the form of nanocrystalline dendrites using the galvanostatic electrodeposition technique. Two distinct morphologies namely, featherlike and globular, were observed under the employed deposition conditions. The featherlike morphology consisted of only the face-centered cubic (fcc)-Al(Mg) phase. However, the globular morphology was composed of the hexagonal close-packed (hcp)-Mg(Al) phase as well as the fcc-Al(Mg) phase. Compositional and TEM studies revealed that both phases were supersaturated and exhibited a nanocrystalline microstructure. Short-time potentiostatic experiments revealed that the formation of these morphologies is dependent on the applied overpotential such that at high overpotentials, only the globular morphology develops, whereas at low overpotentials, only the featherlike morphology is created. These observations are discussed in terms of the deposition rate.

Annealing response of AA5182 deformed in plane strain and equibiaxial strain paths

The annealing response of AA5182 Al–Mg alloy deformed to an effective prestrain of  = 0.15 via plane strain and equibiaxial strain paths is compared. The comparison is done at two temperatures namely, 623 and 673 K. The recovery, recrystallization and grain growth behaviour of this alloy is studied by electron backscatter diffraction and dislocation density estimation using X-ray line broadening analysis. It is found that recrystallization is slower in equibiaxial deformation condition compared to that in plane strain deformation condition during annealing. Significant recrystallization is observed after annealing for 60 s at 673 K and for 480 s at 623 K following plane strain deformation. Furthermore, significant recrystallization is associated with lower grain growth at 673 K (∼55 μm) as opposed to that at 623 K (∼75 μm). The results are explained on the basis of differences in both the strain paths.