Improving Corrosion Resistance of Aluminosilicate Refractories towards Molten Al-Mg Alloy Using Non-Wetting Additives: A Short Review

Abstract

The corrosion of refractories in contact with high temperature aluminum-magnesium alloys leads to contamination of the Al-Mg alloy products by solid impurities from degraded refractories. Where both the spinel and corundum phases form in the refractories, cracks are generated and propagated by diffusion of molten Al-Mg, resulting in severe corrosion. In this review paper, the corrosion phenomenon is discussed, and published work is summarized, supplemented by our recent experimental results. Using the Alcan immersion test, materials based on white-fused mullite (WFM) were evaluated for their corrosion resistance and interfacial behavior. WFM was modified using different 2-wt.% of non-wetting additives (NWAs), such as BaSO4, CaF2, Secar®71 cement and wollastonite to improve their performance when in contact with molten Al-Mg alloy at 850 °C for 96 h. The mechanical properties of the samples such as flexural and compressive strength were evaluated, in addition to X-ray diffraction and microscopic analysis (optical and scanning electron microscopy coupled with X-ray elemental mapping). It was observed that cracks formed in samples were promoted with only BaSO4, CaF2, Secar®71 cement or wollastonite. However, cracks did not appear in the sample promoted with both 1-wt.% CaF2 and 1-wt.% BaSO4, because of improved anti-wetting properties in addition to inhibiting spinel (MgAl2O4) formation, which is the main cause of the cracks. This is a significant finding in the prevention of cracks and improvement of the refractory corrosion resistance.

Proven Anti-Wetting Properties of Molybdenum Tested for High-Temperature Corrosion-Resistance with Potential Application in the Aluminum Industry

“…Samples were analyzed before and after the ALCAN immersion test on a Hitachi S-4700 SEM Field-Emission Scanning Electron Microscope (Tokyo, Japan), equipped with an energy dispersive X-ray (EDX) X-Max Oxford spectrometer (Abingdon, UK), capturing both secondary and backscattered electron images (SEI and BEI) operated at 20 kV [ 4 ]. EDX analysis for elemental composition and distribution in the samples with subsequent X-ray elemental mapping was derived from the SEM imaging.…”

“…Therefore, a permanent solution would be either to add a mould-release agent, which can generate such a coating for moulds that are subjected to a liquid or flowable Al material, or create a method for producing such a coating [ 3 ]. In the Al industry, which produces Al-Mg alloys, corrosion leads to contamination of the alloy products arising from the solid impurities that come from, for example, the sow molds, rotor material, or degraded refractories [ 4 ].…”

“…Normally, the corrosion process begins with the wetting of the solid material by the molten Al liquid as a result of high adhesive forces between them. This is followed by a reaction that creates an interface with a different chemical composition (with a strong effect on the magnitude of the interfacial free energy, and subsequent changes in the contact angle), and if this interfacial material is highly soluble, cracks are opened, more Al liquid penetrates into the material, thus exacerbating the corrosion process [ 4 ]. We are therefore proposing the use of a plasma-sprayed coating with non-wetting characteristics towards molten Al and Al-Mg alloys.…”

Synthesis of Cubic Aluminum Nitride (AlN) Coatings through Suspension Plasma Spray (SPS) Technology

“…The samples were analyzed according to the method described in an earlier article using a "Philips Panalytical X'pert PRO MPD" X-ray diffractometer (PANalytical, Almelo, The Netherlands) [57]. The diffractometer uses Cu Kα1 radiation with a wavelength, λ = 1.54 Å, in the 2θ-angle range from 20 to 100 • , at a scanning speed of 0.04 • 2θ-angle per min and a step size of 0.02 • and step time, 0.5 s. Data collection and data analysis was performed using factory installed JADE software (version 7.8.4 @2020-04-23 © MDI).…”

“…Microscopic imaging by SEM coupled with energy dispersive X-ray spectroscopy (EDX) were used to investigate the morphology, structure, particle size and composition of the materials. In this work, SEM imaging and analysis was done on a "Hitachi S-4700" Field-Emission Scanning Electron Microscope (Hitachi High-Technologies Corporation, Tokyo, Japan), equipped with an EDX X-Max Oxford spectrometer (Abingdon, UK) [57].…”