Michael Kellam

Amorphous Magnesium Sheet Produced by Twin Roll Casting

Sheets of a Mg60Cu29Gd11 alloy were produced by twin roll casting with all operational variables, except roll speed, being kept constant. As a function of the roll speed, the structure of the as-cast sheet changed from being crystalline to fully amorphous and then back to crystalline. Through careful selection of the casting speed that is suitable for the selected alloy system and with which the exit temperature of the sheet remains within the supercooled liquid region, a malleable sheet with no surface defects is produced. This work shows that twin roll sheet casting is a viable process for the production of magnesium-based bulk amorphous sheet in a continuous manner and on an industrial scale.

Post-Hydrogen Permeation Characterization of V-Based Crystalline Alloy Membranes

The surface preparation and hydrogen embrittlement in particular are research challenges facing the practical application of vanadium alloy membranes. These two issues are addressed by surface characterization and fracture analysis in order to find the reasons why delamination and crack failures occur during hydrogen permeation. Post-failure analysis of the hydrogen-induced cracking membrane specimen suggests a new failure mechanism for hydrogen embrittlement.

Formability of Twin-Roll Cast Age-Hardenable Mg-Zn Alloys

The suitability of a twin-roll cast (TRC) age-hardenable alloy for wrought applications is explored. A Mg-4Zn (wt.%) alloy, 3mm thick, was cast using the TRC route. Deviating from the traditional practice of homogenization followed by age-hardening in die/sand cast parts, the TRC sheet, cut into small strips, was hot rolled and annealed after homogenization. They were then deep drawn and subsequently age-hardened. The rollability, mechanical properties and microstructure of the alloy at different stages of processing and after forming, are presented and discussed.