Investigation of Solidification and Precipitation Behavior of Si-Modified 7075 Aluminum Alloy Fabricated by Laser-Based Powder Bed Fusion

Guichuan Li,Carmen M Cepeda-Jiménez,Arturo Martín,Maria L Montero-Sistiaga,Maria San Sebastian,Jeroen Soete,Suraj Dinkar Jadhav,Kim Vanmeensel

doi:10.1007/s11661-020-06073-9

Guichuan Li, Carmen M Cepeda-Jiménez + Show 6 more

Open Access

https://doi.org/10.1007/s11661-020-06073-9

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Abstract

Fabrication of high strength aluminum alloys using laser-based powder bed fusion (L-PBF) encounters challenges, including the occurrence of solidification cracks and the loss of volatile elements, such as Zn and Mg. The current work developed a Si-modified Al7075 alloy aiming at introducing eutectic phases to mitigate the solidification cracking during L-PBF. Based on Kou’s model, the addition of Zn and Mg decreased the crack susceptibility from 6504 °C to 5966 °C, and the addition of 3.74 wt pct of Si further decreased the crack susceptibility to 3960 °C. The Al7075 alloy fabricated by L-PBF exhibited a large amount of solidification cracks extending throughout the sample. Crack-free samples with a relative density of 99.94 pct, as inspected by X-ray microcomputed tomography, were achieved for the developed Si-modified Al7075 alloy. The microstructure showed a transition from a coarse columnar microstructure to a refined mixed columnar + equiaxed microstructure after alloy modification, with a concomitant grain size reduction from 59.0 ± 42.2 to 15.0 ± 9.4 µm. Moreover, Si, Mg2Si, and Al2Cu phases were detected in the Si-modified Al7075 alloy. After a direct ageing heat treatment, the Si-modified Al7075 alloy showed minimal age hardening effect with a peak hardness of (146 ± 3 Hv).

Highlights

LASER-BASED powder bed fusion (L-PBF), known as selective laser melting (SLM), is a powder-based additive manufacturing (AM) technique utilizing a laser as the energy source, allowing to manufacture complex-shaped metal components by additive consolidation of powder layers.[1]
The two Si-modified Al7075 samples that were used for direct ageing heat treatments were fabricated with two different hatch spacing, i.e., 105 lm and 90 lm, resulting in a different hardness in the as-fabricated condition, 140 ± 2 Hv and 134 ± 3 Hv, respectively
This study provides new insights into the development of crack-free high strength Aluminum alloys for Additive Manufacturing (AM)

Summary

Introduction

RR Author ProofLASER-BASED powder bed fusion (L-PBF), known as selective laser melting (SLM), is a powder-based additive manufacturing (AM) technique utilizing a laser as the energy source, allowing to manufacture complex-shaped metal components by additive consolidation of powder layers.[1]. Compared to conventional subtractive manufacturing processes, AM offers immanent advantages for medium-low batch production, owing to its capability to fabricate customized and complex-shaped parts as an integral piece without the need for expensive molds and tooling.[2]

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