Aluminum Parts Fabricated by Laser-Foil-Printing Additive Manufacturing: Processing, Microstructure, and Mechanical Properties

Abstract

Fabrication of dense aluminum (Al-1100) parts (>99.3% of relative density) by our recently developed laser-foil-printing (LFP) additive manufacturing method was investigated as described in this paper. This was achieved by using a laser energy density of 7.0 MW/cm2 to stabilize the melt pool formation and create sufficient penetration depth with 300 μm thickness foil. The highest yield strength (YS) and ultimate tensile strength (UTS) in the LFP-fabricated samples reached 111 ± 8 MPa and 128 ± 3 MPa, respectively, along the laser scanning direction. These samples exhibited greater tensile strength but less ductility compared to annealed Al-1100 samples. Fractographic analysis showed elongated gas pores in the tensile test samples. Strong crystallographic texturing along the solidification direction and dense subgrain boundaries in the LFP-fabricated samples were observed by using the electron backscattered diffraction (EBSD) technique.

Development and experimental study of an automated laser-foil-printing additive manufacturing system

“…This faster heat conduction in LFP prevents creation of large pores, as the generated gas bubbles in the melt pool do not get long enough time to grow in size. This higher cooling rate adjusts the parts' microstructure, resulting in less porosity and higher mechanical properties, as extensively discussed in our previous published work (Hung et al, 2020). A solution to improve the challenge of low heat transfer in the L-PBF process has been reported in the literature through preheating the build plate which helped uniforming the temperature distribution around the melt pool; results showed that preheating the build platform to 150°C decreased the porosity and significantly improved the material's ductility due to the more homogenized cellular microstructure (Nezhadfar et al, 2021).…”

“…To eliminate the surface roughness effect on the mechanical properties, the tensile specimens were cut from the LFP-fabricated parts using wire electrical discharge machining. The miniature tensile bar has dimensions shown in Figure 3, following American Society for Testing and Materials standards (Hung et al, 2020;Kolhatkar et al, 2019). An Instron machine was used to measure the tensile specimens with a clip-on extensometer at the crosshead speed of 0.015 1/min (strain rate per minute) (Jirandehi and Khonsari, 2021;Ghadimi et al, 2021).…”

“…Depending on the used process parameters, the generated energy density varies, which consequently impacts the melt pool depths, part's dimensional accuracy and mechanical properties. True adjustment of these process parameters requires the comprehensive understanding of the relationship among part's characteristics and process parameters (Hung et al, 2020). Such a relationship between melt pool depths and process parameters were developed by Sehhat et al through performing thorough statistical analysis on the metallography results of melt pool depths created by various levels of process parameters (Sehhat et al, 2021b).…”

“…Due to the higher cooling rate of foil feedstock in LFP than the powder bed in L-PBF, the generated heat can more rapidly be transferred to the printed layers and build platform. This higher cooling rate also resulted in finer grain structures in the LFP parts (Hung et al, 2020). Another advantage of deploying foil feedstock in LFP is the lower oxygen content compared to the L-PBF process, due to the foil's less tendency to oxidation provided by the much smaller surface area in foil than powder (Hung et al, 2019).…”

“…LFP has been demonstrated to fabricate amorphous and crystalline metal parts, including Zr-based metallic glass, 304L stainless steel (SS), Al-1100, and AISI 1010, resulting in high part density and mechanical strength (Hung et al, 2019; The current issue and full text archive of this journal is available on Emerald Insight at: https://www.emerald.com/insight/1355-2546.htm Hung et al, 2020;Chen et al, 2017). This process has also been demonstrated to build composite sandwich structures (Hung et al, 2019).…”