A review of Laser Powder Bed Fusion Additive Manufacturing of aluminium alloys: Microstructure and properties

Additive manufacturing (AM) of metallic alloys for structural and functional applications has attracted significant interest in the last two decades as it brings a step change in the philosophy of design and manufacturing. The ability to design and fabricate complex geometries not amenable to conventional manufacturing, and the potential to reduce component weight without compromising performance, is particularly attractive for aerospace and automotive applications. This has culminated in rapid progress in AM with Ti- and Ni-based alloys. In contrast, the development of AM with Al-alloys has been slow, despite their widespread adoption in industry owing to an excellent combination of low density and high strength-to-weight ratio. Research to date has focused on castable and weldable AlSiMg-based alloys (which are less desirable for demanding structural applications), as well as on the development of new AM-specific AlMgSc alloys (based on 5xxx series). However, high strength wrought Al-alloys have typically been unsuitable for AM due to their unfavourable microstructural characteristics under rapid directional solidification conditions. Nevertheless, recent research has shown that there is promise in overcoming the associated challenges. Herein, we present a review of the current status of AM with Al-alloys. We primarily focus on the microstructural characteristics, and on exploring how these influence mechanical properties. The current metallurgical understanding of microstructure and defect formation in Al-alloys during AM is discussed, along with recent promising research exploring various microstructural modification methodologies. Finally, the remaining challenges in the development of AM with high-strength Al-alloys are discussed.