The effects of large amounts of Sr addition on the solidified structures and hot tearing of Al-6mass%Mg-3mass%Si alloys cast into the I-beam shaped mold were investigated by OM, SEM-EDS observations. The hot tearing of 0.04mass%Sr added alloy was less than Sr free alloys, due to the refinement of secondary crystallized eutectics, such as Mg2Si and α-Al phases. On the other hand, when the Sr content in Al-6mass%Mg-3mass%Si alloys was above 0.04mass%, the area fraction of the hot-tearing region increased. This tendency for the hot tearing region to increase is caused by the crystallization of the Al-Si-Sr intermetallic compound. These findings suggest that the reasons for the increase in hot-tearing with the addition of large amounts of Sr affect the time of occurrence of two types of compounds (fine plate and coarse plate), the difference in their concentrations and frequency of occurrence.
When cemented carbide contacts molten cast iron during the insert casting process, the binder phase of the cemented carbide is thought to melt even if the molten temperature of the cast iron is lower than the solidus temperature of the cemented carbide (1593 K). It is important to understand the melting mechanism to clarify the interface formation mechanism, and subsequently control the interface structure. The purpose of this study is to clarify the interface formation mechanism from the microstructural change of cemented carbide dipped in molten cast iron. A round bar specimen made of cemented carbide was dipped in molten cast iron at 1473 to 1596 K, and pulled up after a predetermined time. Microstructure observation, elemental analysis, and hardness test were performed on the cross-section of the specimen. The specimen changed from a homogeneous sintered structure to a two-layer structure, the center side was a non-reacted layer that did not change, and the outer side was the transition layer where melting had occurred. The diffusion of Fe and C is thought to have decreased the solidus temperature of the binder phase significantly that the binder phase melted. The non-reacted layer radius could be expressed by the rate equation derived from the Nernst-Brunner equation. Structural changes were seen at the interface such as increased outer diameter of the cemented carbide round bar specimen, occurrence of shrinkage cavities in the transition layer, and characteristic concentration of Co at the boundary. These are thought to be due to liquid phase migration occurring in the molten binder phase and decreased WC solubility due to the increase in Fe concentration.