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Investigation of solidification and precipitation behavior of Si-modified 7075 aluminum alloy fabricated by laser-based powder bed fusion
Journal Contribution - Journal Article
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).
Journal: Metallurgical & Materials Transactions. Part A
Pages: 194 - 210