Metal additive manufacturing: Processing, microstructures and mechanical properties

As a transformative manufacturing technology, metal additive manufacturing has surpassed the constraints of conventional techniques in customized design and integrated structural forming, exhibiting the broad application prospects in the fields of aerospace, automotive industry, and biomedical engineering. To secure a leading position in the global competition for advanced manufacturing science and technology and to address the formidable challenges posed by the international situation, some countries have established strategic initiatives focused on metal additive manufacturing. Against this backdrop, metal additive manufacturing has achieved remarkable advancements over the past 30 years. In this paper, we first reviewed the evolution of metal additive manufacturing technologies, and briefly introduced their classification, principle and main characteristics. Using the laser powder bed fusion process as a representative example, we summarized the influences of laser power, scanning speed, scanning spacing and scanning strategy on the material microstructures. We further concluded the formation mechanisms and control methods of various defects during metal additive manufacturing process, and highlighted the unique structures and superior properties enabled by innovative processes and design approaches across different metal material systems. We also emphasized the importance of investigating the micro-mechanical properties in revealing the correlation between the unique microstructures of AM metals and their macroscopic mechanical behaviors. Finally, we pointed out the current challenges confronting metal additive manufacturing technology and offered insights into future development, with a goal of advancing scientific research and technological innovation in this area.