Overview of Al-Si alloys for additive manufacturing and prospects

Abstract

Additive manufacturing (AM) has emerged in recent years for enabling the generation of parts with highly complex geometries. Due to the nature of the AM process, which causes alloys to experience a complex thermal history during processing, there is a need to develop alloys that are suitable for this process. Al-Si alloys were widely used in many industries, such as automotive and aerospace, being of great interest for their excellent mechanical properties, processability and low density. Over the last years, several studies have reported suitable results Al-Si based alloys processed by AM. However, some Al-Si alloys compositions need to be further investigated, encompassing the effects of alloying elements on the properties of interest as well microstructural features, especially on the eutectic silicon size/morphology and growth of other secondary phases. This study evaluated the main Al-Si alloys that are highlighted for AM processes, as well as used alloying elements and new options for chemistries that would be suitably employed. The main AM techniques are discussed, pointing out their advantages and the challenges according to the inherent characteristics of the process. Alloying elements were evaluated considering their impact on Si morphology and mechanical properties on produced parts.. Among the evaluated elements, Ni and Zn additions proved to be effective in increasing the mechanical strength of the analyzed alloys. Zr and rare earths such as Sc and Ce demonstrated efficiency as refining agents for Si morphology, which also enhances the alloys properties. Two heat treatments showed to be effective, T6 and T73, aging and two-stage aging, respectively. Both treatments increased the hardness of treated alloys, however, more investigation appears to be needed. Evaluating all aspects, the most used alloy nowadays is the Al-Si10Mg due to its optimal properties if processed within a processing window having laser power ranging from 170 to 200 W and scanning speeds from 700 to 1400 mm/s. In sum, Ni, Zn, Zr and rare earth elements such as Sc and Ce demonstrated to be promising as alloying elements for the Al-Si alloys, being excellent topics for future investigations. Combining Sr with rare earths presented a great synergy in terms of microstructural refinement, being a suitable alternative for alternatives alloys to be developed.