Additive manufacturing is a near-net shaping technology that builds three-dimensional solid parts by depositing material layer by layer. It offers unique advantages in producing metal parts with complex structures. As a result, it has been widely used in key fields such as aerospace, biomedical and high-end mold manufacturing. However, the unique forming process of additive manufacturing introduces defect characteristics that differ from those in traditional manufacturing methods. These issues severely affect the service reliability of the formed parts and have become a critical challenge for the technology. This paper systematically summarizes the research findings of AECC Additive Manufacturing Technology Innovation Center on defects in additively manufactured metal materials. It focuses on the morphological features, formation mechanisms and effects on mechanical properties of typical defects such as holes, lack of fusion, inclusions and cracks. The paper also analyzes the role of hot isostatic pressing in closing defects and improving mechanical properties. To address current research gaps, it suggests further studies in several areas. These include revealing the relationship between defect formation mechanisms and process parameters, developing metal materials specifically for additive manufacturing, establishing defect acceptance standards based on part service requirements, and advancing intelligent online monitoring and closed-loop control technologies. These efforts aim to promote further progress of additive manufacturing.

Additive manufacturing is a new manufacturing technique that integrates laser, digitization, materials and other disciplines. It has the advantages of dimensionality reduction manufacturing, complex forming, and high material utilization. It is one of the most promising techniques in the field of material processing. Metal additive manufacturing technique has been widely studied and applied in the aviation field. The research on the additive manufacturing of aviation metal materials by domestic and foreign scholars continues to deepen. AECC Additive Manufacturing Technology Innovation Center has carried out a quantity of research and obtained some data from the four factors of metal additive manufacturing: microstructure, defects, surface and configuration. Some phenomena and laws have been found, including the characteristics and influencing factors of microstructure continuous growth; influence of the structure on mechanical properties; the characteristics and causes of common defects（pores, cracks, incomplete fusion） in additive manufactured typical materials and their influence mechanism on mechanical properties, especially fatigue properties; the relation between surface roughness and forming angles, and the influence of surface states on fatigue properties; factors influencing configuration of metal additive manufacturing. Finally, the problems existing in the development of metal additive manufacturing are summarized, and the suggestions for future research and development are put forward.