Corrosion Mechanisms of Steel and Cast Iron by Molten Aluminum

Abstract

International audienceThe corrosion mechanisms by liquid aluminum of three industrial materials have been studied: unalloyed steel (UAS), and ferritic and modified pearlitic cast irons (FCI and PCI, respectively). The behavior of these materials when in contact with liquid aluminum is different. Aluminum diffuses deep into the UAS and forms intermetallic compounds with iron at the surface and in the steel matrix. At the surface, only Fe2Al5 and FeAl3 are found. In the matrix, FeAl2 also is formed in agreement with the equilibrium Fe-Al diagram. From the matrix to FeAl2, the Al content in the ferrite increases progressively until Al saturation is reached. At this step, black elongated precipitates (Al4C3 and/or graphite) appear. Graphite lamellas present in both FCI and PCI constitute an efficient barrier to the Al diffusion. The high silicon content of the FCI leads to the formation of a phase free from Al and saturated in Si. For the PCI, a thin layer rich in Al and Si, which is formed between the matrix and Fe2Al5, limits the diffusion of atoms. The effects of Cr and P added in the PCI also are discussed

Study of corrosion mechanism of cast iron in molten aluminum

“…In figure 8(b), there are some black needle-like precipitates in the IMC and Al, Si-rich regions near the Interface 2. These precipitates were also found in the study of Balloy D. [10], which gave the assumption that these precipitates were Al 4 C 3 or small flake graphite transformed by cementite in pearlite. According to the Balloy D. study, Al 4 C 3 is usually present in the form of (Fe 3 C) x (Al 4 C 3 ) y in pearlitic cast iron, and when the Al content exceeds 17%wt, Al 4 C 3 decomposes into graphite.…”

“…The darkest area is solid Al, the middle is IMC, and the brighter is cast iron. There are many free rod-shaped Fe-Al IMCs in solid aluminum [10]. Also, graphite is present in IMC and solid aluminum in corrosion samples.…”

“…The change in lattice constants allows more C atoms to enter the lattice gap of α-Fe, causing supersaturation of C elements. When the C and Al contents are saturated, Al 4 C 3 is produced, and because of the increasing Al content, Al 4 C 3 decomposes to produce graphite [10].…”

“…The thickness of IMC layers declined from 4 to 0.2 μm with friction time decreasing from 40 to 10 s, while a 15 welding groove machined on the end of steel helped realize thinning of IMC layer to a thickness of 0.3 μm. Balloy D et al [10] studied the corrosion mechanism of unalloyed steel (UAS), ferritic cast iron (FCI) and pearlite cast iron (PCI) in aluminum liquid and found that Al has the largest diffusion depth in UAS. The flake graphite in FCI and PCI can effectively prevent the diffusion of Al.…”

Study of protective coatings for aluminum die casting molds

“…Hot-work components are generally affected by failure mechanisms (Fig. 1) such as erosion, corrosion, wear, and thermal fatigue [1][2][3][4]: all these mechanisms directly involve the surface. The difficulties coming from the corrosion of the tool's surface during service create a serious problem in the manufacturing of castings [5,6].…”