The applicability of a cast-coating process for improving the oxidation resistance of cast Ni-based superalloys was evaluated. Specifically, metallic plates of Pr, Ir, and Re expected to improve oxidation resistance when they are enriched on the cast alloys were placed in a mold and cast coating using Ni-10at%Al alloy was performed in order to investigate the formation of the Pt, Ir, or Re-enriched layer on the casting surface. Then the microstructure of the Ni-based alloy/specimen interface was observed. To analyze the concentration profile in the interdiffusion region, solidification and diffusion simulations were performed. It was found that Pt easily dissolves into the molten Ni-based alloy, and Re can not expected to modify cast metal surfaces due to its low solubility into the Ni-10at%Al alloy. On the other hand, Ir forms smooth interdiffusion layer, and numerical calculations predicted that Ir can maintain the modification ability even in a process time of 1 hour, which is equivalent to the casting time of Ni-based turbine blades.

  Casting CAE is used practically to predict casting defects and in the casting design of the ingate system. However, the prediction accuracy of defects caused by flow dynamics such as air and gas entrainments, miss run, oxide film, etc. is not sufficient. So, it is important to analyze the mechanism of air entrainment and gas generation and accurately predict how the gas moves.

  In the present study, we observed air bubbles moving during the mold filling of die casting using a water model experimental apparatus and tried to simulate the bubble behavior using the marker function of the casting CAE software. The results using the marker function could not estimate the experimental ones accurately. For this reason, bubble tracking experiments using a circulating water tank was conducted and the governing equation for air movement with the virtual mass term was established. The results of calculating air movement using the modified air movement equation were almost the same as the experimental ones during mold filling in die casting experiments using the water model, providing some information on the forces acting on the bubbles moving in the fluid.

  Non-heat treatment Al-Mg-based die casting alloys have been developed for automotive structural parts. In previous studies, alloy compositions with at least 1.0%Si have been proposed to reduce hot tearing susceptibility (HTS). Adversely, the increase in Si content reduces ductility. For some automotive body structures, Al-Mg alloy die castings with Si content exceeding 1.0% should not have the required ductility. Up to the authors' knowledge, there have been no previous reports on the development of the Al-Mg-based die casting alloy that maintains high ductility and reduces the HTS with a small amount of Si. This study aims to develop an Al-Mg alloy with both high ductility and low HTS by investigating the following three items on an Al-4.5Mg-1.0Mn alloy with 0.2%Si added : (1) additional elements to reduce the HTS, (2) associated mechanical properties (requirements by automotive company : yield stress ≥ 140 MPa and fracture elongation ≥ 15%), and (3) the mechanism of decreasing HTS.

  It was revealed that the co-addition of 0.025%Sr, 0.08%Ti, and 0.016%B reduces HTS when the hydrogen content of the melt was 0.5 to 1.0 mL/100gAl. Furthermore, the yield stress and fracture elongation of a lower link arm produced via HPDC with the above composition were found to achieve the requirements. It was also indicated that the mechanism of decrease in the HTS by Sr addition should result from the decrease in the thermal tensile load due to the formation of hydrogen porosity at a lower solid fraction than that without Sr. It is suggested that when 0.025%Sr, 0.08%Ti, and 0.016%B are added to the Al-4.5Mg-1.0Mn-0.2Si alloy, non-heat treatment automotive body parts with both high ductility and low HTS will be obtained by high pressure die casting..