Microstructure and corrosion evolution of additively manufactured aluminium alloy AA7075 as a function of ageing

Additively manufactured high strength aluminium alloy AA7075 was prepared using selective laser melting. High strength aluminium alloys prepared by selective laser melting have not been widely studied to date. The evolution of microstructure and hardness, with the attendant corrosion, were investigated. Additively manufactured AA7075 was investigated both in the as-produced condition and as a function of artificial ageing. The microstructure of specimens prepared was studied using electron microscopy. Production of AA7075 by selective laser melting generated a unique microstructure, which was altered by solutionising and further altered by artificial ageing - resulting in microstructures distinctive to that of wrought AA7075-T6. The electrochemical response of additively manufactured AA7075 was dependent on processing history, and unique to wrought AA7075-T6, whereby dissolution rates were generally lower for additively manufactured AA7075. Furthermore, immersion exposure testing followed by microscopy, indicated different corrosion morphology for additively manufactured AA7075, whereby resultant pit size was notably smaller, in contrast to wrought AA7075-T6.Comment: 37 pages, includes 4 Tables and 11 Figure

Unravelling the characteristics of Al-alloy corrosion at the atomic to nanometre scale by transmission electron microscopy

The localised corrosion associated with Mg2Si in the Al-matrix of an Al-Mg-Si alloy was studied in 0.1 M NaCl at pH 6 by quasi in-situ transmission electron microscopy. Herein, physical imaging of corrosion at the atomic to nanometre scale was performed. Phase transformation and subsequent chemical composition variations associated with the localised corrosion of Mg2Si were studied. It was observed that corrosion initiated upon Mg2Si, often preferentially at the interface with the Al-matrix, and propagated until Mg2Si was completely dealloyed by Mg-dissolution, resulting in an amorphous SiO-rich phase remnant. The SiO-rich remnant became electrochemically inert and did not initiate corrosion in the Al-matrix. This study provides a clear understanding on the localised corrosion of Al-alloys associated with Mg2Si. In addition, the methodology followed in this study can also be applied to understand the role of precipitates and second phase particles in the localised corrosion of Al-alloy systems

Methodologies for operando ATR-IR spectroscopy of magnesium battery electrolytes

We explore the suitability of operando attenuated total reflection infrared (ATR-IR) spectroscopy methodologies for the study of organoaluminate electrolytes for Mg battery applications. The "all-phenyl complex" in tetrahydrofuran (THF), with the molecular structure [Mg Cl ·6THF] [AlPh ] , is used as an exemplar electrolyte to compare two different spectroelectrochemical cell configurations. In one case, a Pt gauze is used as a working electrode, while in the second case, a thin (∼10 nm) Pt film working electrode is deposited directly on the surface of the ATR crystal. Spectroscopic measurements indicate substantial differences in the ATR-IR response for the two configurations, reflecting the different spatial arrangements of the working electrode with respect to the ATR sampling volume. The relative merits and potential pitfalls associated with the two approaches are discussed

Analysing the degree of sensitisation in 5xxx series aluminium alloys using artificial neural networks: A tool for alloy design

The 5xxx series aluminium alloys are susceptible to sensitisation during service at elevated temperatures. Sensitisation refers to deleterious grain boundary precipitation resulting in rapid intergranular corrosion in moist environments. A holistic understanding of the variables that can influence the degree of sensitisation in Al-Mg-Mn alloys is presented herein, including the exploration of some custom produced 5xxx series alloys that were prepared to create a significant dataset for which an artificial neural network (ANN) could be applied. An ANN model could reveal complex interactions between various factors that influence sensitisation, with the view to designing sensitisation resistant Al-Mg-Mn alloys.Author Q. Li thanks the National Key Research and Development Program of China (Grant No. 2017YFB0702100), the Shanghai Science and Technology Committee (No. 16DZ2260601) and the National Natural Science Foundation of China (No. 51871138). Financial support from the Office of Naval Research and Office of Naval Research Global (with Dr. Airan Perez and Dr. Liming Salvino as Scientific Officers) is gratefully acknowledged. Characterisation herein was conducted at the Monash Centre for Electron Microscopy