The effect of sensitisation on 5xxx series aluminium alloys

Aluminium (Al) and its alloys represent the commodity ‘light metals’ and have had continued usage and intense interest from industry and the academic field since their large-scale industrial implementation commencing approximately 100 years ago. Various properties can be achieved in Al-alloys which arise from alloying with many other elements. Al-alloys can provide corrosion resistance, formability, weldability, strength and damage tolerance; however the actual combination of such properties is nominally a trade-off. As a result a wide range of carefully engineered Al-alloys are applied across different fields. This includes shipbuilding, where density, weldability, and corrosion resistance are key properties. Despite the advantages of Al-alloys in marine applications, severe intergranular corrosion (IGC) damage can take place after a prolonged service time at elevated temperature. This concern originates from a supersaturation of magnesium (Mg) in the common marine alloys (based on the Al-Mg system) which can form deleterious anodic Mg2Al3 β-phase) particles at grain boundaries. Herein, this process is termed “sensitisation” as it reflected a detrimental microstructural evolution. Although the β-phase evolution is the main factor for sensitisation induced damage, there are yet to be any critical studies on microstructural evolution prediction (experiment or modelling), in a deterministic sense. This project aims to cover the various principal factors that dictate microstructure and the influence upon intergraular corrosion from sensitisation. This is done with the view towards a science-based tangible and practical reversion heat treatment to repair sensitised Al-Mg alloys.