Left: Automotive frame with steel and aluminium parts welded together. Centre: Interface between aluminium and copper in an atomistic simulation before and during weld process. Right: Transmission electron microscopy image of interface between copper and a copper-aluminium intermetallic compound. The Cu/Al interface is used for illustrative purposes as a stand-in for the Fe/Al interface.

Supervisors: Peter Brommer (Engineering), Prakash Srirangam (experimental, WMG)

Summary:

Aluminium and steel are widely employed metallic materials for automotive applications, such as in vehicle frames. Joining of these two dissimilar metals by fusion welding results in formation of brittle aluminium-iron compounds at the interface, which degrade the performance of the weld. Looking at the motion of individual atoms, we will use modelling techniques such as Molecular Dynamics (MD) and Kinetic Monte Carlo (KMC) combined with transmission electron microscopy analysis to study how iron and aluminium atoms react at the weld interface to find weld conditions where favourable intermetallic compounds form at interface.

Background:

Dissimilar metals joining is gaining importance in various engineering applications such as automotive, aerospace, batteries and electronic industries. Aluminium (Al) and steel are two major important materials used in the automotive sector. Joining these two materials is always challenging due to their differences in physical and mechanical properties. Also, joining of steel to Al by fusion welding methods such as laser welding results in formation of brittle iron intermetallic compounds (IMC) in the weld zone which hampers the mechanical properties. The weld zone properties ultimately depend on the type of IMCs, their average size, shape and distribution. The formation of IMCs at the weld joint greatly depends on the mutual solubility of iron (Fe) and aluminium (Al), diffusion of atoms at the interface, presence of dislocations etc. A better understanding of IMCs formation during laser welding of dissimilar steel to Al would not only lead to improved mechanical properties of weld joints, but also help to achieve net zero emissions with usage of light-weight materials for engineering applications.

In this project, we focus on understanding the interaction between Fe and Al atoms at the weld interface during fusion welding of steel to Al alloy. In the Brommer group, we will employ atomic level modelling techniques, particularly molecular dynamics (MD) and Kinetic Monte Carlo (KMC), to study atomic motion during and after laser irradiation, as well as the mechanical properties of the weld. The effect of weld parameters on interfacial properties, vacancies and dislocations via mutual diffusion of Fe and Al will be experimentally supported with TEM microscopy analysis performed at WMG (Srirangam Group). Image recognition techniques would then allow direct comparison between simulation and experiment.

Project Objectives for the PhD project:

This project would suit a student interested in developing and improving atomic scale simulation models of this technologically and industrially highly relevant process. The integration with experimental materials characterisation measurements is a key feature of this project. There are also international collaboration opportunities, e.g. with the University of Stuttgart for the simulation of laser-matter interactions.