Sustainable recycling of aerospace-grade ultra-clean 7050 aluminum alloy melts through argon refining without secondary aluminum dross generation

The refining of aluminum scraps commonly employs nitrogen-fluxes to eliminate impurities. However, the aluminum nitride (AlN) generated by the reaction between nitrogen and the aluminum melt, along with residual fluxes, contribute to low cleanliness of the recycled aluminum melt and pose difficulties for the disposal of secondary aluminum dross (SAD). Our innovative research has resulted in the recycling of aerospace-grade clean aluminum alloy melts. The results indicate that the argon bubble floating process adsorbs inclusions and hydrogen, achieving an aerospace-grade ultra-clean melt. The solid-liquid interface between the tube wall and the melt provides a diffusion channel for hydrogen atoms, and the bubbles rising up along the wall lead to a higher hydrogen content in the melt. The argon refining dross is primarily composed of Al and Al2O3, which can be recycled as a raw material for aluminum electrolysis. Argon refining can decrease the hydrogen content and the number of inclusions with particle size >= 40 mm in the recycled aluminum melt to the level of aerospace aluminum alloy melt. Nonetheless, the particle size >= 20 mm remains 1.5-2.5 times that of primary aluminum.(c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The conventional refining of aluminum scraps using nitrogen-fluxes often leads to the generation of aluminum nitride and residual fluxes, resulting in low purity of the recycled aluminum melt and difficulties in disposing of secondary aluminum dross. Our innovative research has achieved the recycling of aerospace-grade clean aluminum alloy melts, utilizing the argon bubble floating process to remove impurities and hydrogen, and achieving an ultra-clean melt. The argon refining dross can be recycled as a raw material for aluminum electrolysis, and the hydrogen content and the number of inclusions in the recycled aluminum melt can be reduced to the level of aerospace aluminum alloy melt, except for the inclusions with particle size >= 20 mm, which still remain a challenge.