Characterization of the deposit-foaming of pure aluminum and Al-Mg-0.7Si alloys using directed energy deposition based on their metallurgical characteristics and compressive behaviors

Abstract

This study focuses on the manufacturing of porous materials using the directed energy deposition (DED) technique, which is a 3D printing technique. A foaming agent was mixed with pure aluminum and Al-Mg-0.7Si powder to produce deposited aluminum foam, and its foaming characteristics, metallic structure, and compressive properties were analyzed. The foaming agent formed pores inside the deposited materials through a chemical reaction, and it produced Al 3 Ti, an inter-metallic compound, through the reaction with aluminum powders. Kirkendall voids were generated by the dispersion of Al 3 Ti. Despite the generated inter-metallic compound, no distinct changes were observed in the micro-hardness of the foamed materials compared to that of the non-foamed materials. We also analyzed the effects of laser power on the porosity, number of pores, and deposited height. We fabricated porous materials with a maximum porosity of 35.26% at a laser power of 1100 W using pure aluminum, and fabricated porous materials with a maximum porosity of 18.56% using the Al-Mg-0.7Si alloys. During the deposition process, pure aluminum formed oxide particles more easily compared to the alloys. Consequently, the oxides stabilized the generation and growth of pores, leading to high porosity in pure aluminum. Furthermore, spherical pores were uniformly distributed in pure aluminum, whereas merged pores with irregular shapes were distributed in Al-Mg-0.7Si. This difference is attributed to the viscosity of different melting pools. In the compression test of the non-porous and porous samples, although Young’s modulus and compressive strength were reduced by the internal pores, the specific energy absorption of deposited-foamed samples was higher than that of non-porous materials. The internal pores were compressed and disappeared due to the compressive load, but for Kirkendall voids around Al 3 Ti, they were not completely closed, remaining as micro-pores.