Abstract
In this study, a novel metal matrix composite based on 60 vol% 316L stainless steel and 40 vol% MgO manufactured by powder metallurgy technology was developed. The corrosion resistance of the developed steel–MgO composite material against molten aluminum alloy AlSi7Mg0.3 was investigated by means of wettability tests and long-term crucible corrosion tests. The wettability tests were carried out using the sessile drop method with the capillary purification technique in a hot-stage microscope (HSM). Static corrosion tests were performed in molten aluminum alloy at 850 °C for 168 h to evaluate the impact of pre-oxidation of the composite surface on the corrosion resistance. The pre-oxidation of steel–MgO composites was carried out at 850 and 1000 °C for 24 h, based on preliminary investigations using thermogravimetry (TG) and dilatometry. The influence of the pre-oxidation on the composite structure, the corrosion resistance, and the phase formation at the interface between the steel–MgO composite and aluminum alloy was analyzed using SEM/EDS and XRD. The impact of the steel–MgO composite material on the composition of the aluminum alloy regarding the type, size, and quantity of the formed precipitations was investigated with the aid of ASPEX PSEM/AFA and SEM/EBSD. It was revealed that the pre-oxidation of the steel–MgO composite at 1000 °C induced the formation of stable MgO-FeO solid solutions on its surface, leading to a significant increase of long-term corrosion resistance against the liquid aluminum alloy.
Highlights
The chemical reactivity of molten aluminum alloys in contact with steel-based materials is well known and has already been widely studied [1,2,3,4]
This study focuses on the development of steel matrix composites reinforced by MgO and on the investigation of their corrosion resistance, the contribution of an in situ formation of a passivated mixed oxide layer on the surface of the steel–MgO composite due to the pre-oxidation
Pre-oxidation treatment was carried out to induce the formation of a passivation interface layer with increased corrosion resistance against molten aluminum alloy
Summary
The chemical reactivity of molten aluminum alloys in contact with steel-based materials is well known and has already been widely studied [1,2,3,4]. No studies on the corrosion resistance of stainless steel against molten aluminum or aluminum alloy using long-term crucible tests were found in the literature search. Conventional refractory materials used for contact with molten aluminum and its alloys in different kind of furnaces are based on coarse-grained alumina–mullite castables with antiwetting agents to reduce the infiltration phenomena. Multiple studies in the field of steel–ceramic composites present their ability to be produced in a made-to-order fashion [36,37,38] Their ability to form a reliable protective layer that can not be infiltrated and corroded by aluminum alloys makes steel–ceramic composites favorable substitutes for conventional refractory ceramics, especially for applications requiring refractory parts with sophisticated shapes, such as stirrers and lances. This study focuses on the development of steel matrix composites reinforced by MgO and on the investigation of their corrosion resistance, the contribution of an in situ formation of a passivated mixed oxide layer on the surface of the steel–MgO composite due to the pre-oxidation
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