M. Asle Zaeem

Investigating thermal effects on morphological evolution during crystallisation of hcp metals: three-dimensional phase field study

Abstract Computational models simulating the crystallisation of hexagonal close packed (hcp) metals have traditionally used simple solid/fluid interface anisotropy relations. However, this method does not provide a proper representation of the crystallisation anisotropy, particularly for non-isothermal crystallisation. In this work, we used a phase field (PF) model to investigate the effects of thermal properties (thermal diffusivity and latent heat) on the morphological evolution of hcp metals during crystallisation. The governing equation of the PF model was coupled to the temperature evolution equation, and a three-dimensional model was developed in a finite element framework using COMSOL software. We applied the model to study the crystal formation and evolution of magnesium and yttrium. The unique aspect of this work is that we used Qin and Bhadeshia’s three-dimensional interface anisotropic model to accurately simulate solid/fluid interface anisotropy. The results showed that the thermal effects significantly influenced the shape evolution of the crystals and can control the formation of potential sites for void nucleation inside the crystal structures.

On laser welding of thin steel sheets

Abstract This paper presents a process–structure–property relationship study of laser welds as a continuous consolidation method for joining thin monophased steel foils, thereby providing a more effective, less costly method to construct automotive catalytic converters. A body centred cubic (bcc) iron–chromium–aluminium alloy doped with Mischmetal was utilised in this study. Both pulsed and continuous wave modes were used to establish the limit welding diagrams for lap joint configuration. Actual laser welding parameters were selected using several testing conditions. The laser welds behaved substantially different from the base material under creep and high temperature oxidation. The difference was mainly attributed to the changes in grain morphology, precipitation of aluminium nitrides and carbides, and relocalisation of the reactive elements during liquid metal flow upon keyhole formation, solidification and cooling.