Relationships between the characteristics of porosity, melt pool and process parameters in laser powder bed fusion Al Zn alloy

Abstract

Porosity is one of the main defects in Al alloy fabricated by laser powder bed fusion (L-PBF). This paper investigated the relationships between the characteristics of porosity, melt pool and process parameters in L-PBF Al Zn alloy. It is found that except the laser power and scan speed, the defocusing amount also has a great influence on the melt pool mode. Under the same laser power and scan speed, changing the defocusing amount results in multiple melt pool modes. In this study, keyhole mode melt pool exists only in small defocusing amount of -2 mm and +2 mm. Conduction mode melt pool exists in all defocusing amount. It is also found that the mode of melt pool and the porosity characteristics are closely related and both are significantly influenced by the process parameters. The melt pool depth increases as laser power increases or scan speed decreases during the process of L-PBF Al Zn alloy. Ratio of melt pool depth to width linearly increases with the growing of the laser energy density. Gas porosity and keyhole porosity exist in keyhole mode melt pool. Lack-of-fusion porosity exists in conduction mode melt pool. Relative densities were measured in this research at different process parameters. The highest relative density can be reached to 99.89%. This study is beneficial for the control of the porosity in L-PBF Al Zn alloy. • Relationship between the characteristics of porosity, melt pool and process parameters in laser powder bed fusionL-PBF Al Zn alloy was obtained. • The characteristics of the porosity are closely related to the melt pool mode. • Keyhole mode melt pool only exists in small defocusing amount of ±2mm at high laser energy density in this research.