Effect of Powder Characteristics on Relative Density and Porosity Formation During Electron Beam Selective Melting of Al2024 Aluminum Alloy

Abstract

Defects, such as pores and cracks, can be found in parts fabricated by powder-bed additive manufacturing techniques. The origin of certain defects, such as some voids, can be linked to initial powder quality, which makes it an important factor in the process. Powders used in additive manufacturing processes are produced by different methods such as gas atomization (GA), plasma atomization (PA), and plasma rotating electrode process (PREP); each gives different powder quality. In this study, two different Al2024 powders, produced by electrode induction GA and PREP techniques, were used to investigate the effect of powder characteristics on defect formation during electron beam melting process (EBM). Powders were first characterized by using Hall flowmeter funnel and scanning electron microscope (SEM); then, the EBM process was carried out, and finally, samples were examined by density measurement using Archimedes method, SEM analysis, and tensile test. PREP powder showed higher levels of sphericity and surface smoothness without attached satellites. Consequently, a higher apparent density and decreased flowing time were achieved in PREP powder. Moreover, gas-induced internal pores were observed in GA particles. The results also revealed the average relative density of 96.7% and 99.4% for the parts built by GA and PREP powders, respectively. SEM micrographs confirmed the results of density measurement of the fabricated parts and showed higher degrees of both spherical and irregular-shaped pores in samples built by GA powder. Additionally, they showed deprived mechanical properties due to the higher porosity contents which can form stress-concentrated areas.