Erosion Behaviors and Mechanisms of Low-Carbon Steel and Alloy Tool Steel in Commonly Used Molten Aluminum Alloys

The erosion behaviors and mechanisms of low-carbon steel and alloy tool steel in several commonly used molten Al alloys were investigated via erosion testing. The erosion ratio of the low-carbon steel generally increased as the Si content of the melt increased and decreased as the Fe content of the melt increased. The erosion (dissolution) rate of low-carbon steel corresponded to the difference between the saturation solubility of Fe in the melt at the testing temperature (dependent on the Si content) and the Fe content of the melt via the same mechanism as that described by the Noyes–Whitney–Nernst equation. Conversely, the erosion rate of alloy tool steel (JIS SKD61) was almost constant, irrespective of melt composition. Moreover, the thickness of the semi-solid (diffusion) layer at the contact interface between the melt and alloy tool steel increased with the Si content of the melt. These trends are observed because the local increase in the apparent viscosity of the melt at the contact interface due to suspended carbide particles from the alloy tool steel negated the effects of the saturation solubility of Fe and the Fe content of the melt on the erosion rate.