MATERIAL PROPERTIES OF DIE-CASTING DIE AROUND HEAT-CHECKING CREATED BY A HIGH-PRESSURE ALUMINUM ALLOY DIE-CASTING OPERATION

Abstract In this study, the material properties of a nitride die-casting die exhibiting heat-checking after the die-casting process were experimentally investigated using various methods. Based on the obtained results, the authors believe that several possible mechanisms underlying the formation of heat-checking can be identified. The microstructure of the die-casting die near the heat-checking region is characterized by equiaxed grains along the vicinity of the prior γ -grain boundaries, resulting from the lath martensitic formation. Additionally, numerous Cr–Mo–V-based nitride particles, approximately 100 nm in diameter, are precipitated. The surface hardness of the die-casting die, enhanced by nitriding, induces compressive residual stresses and increases adhesive forces. As a result of changes in microstructural characteristics and crack formation, the stress state near the die-casting die is altered, where compressive residual stresses, observed in the die-casting die, are released, leading to the tensile residual stresses. This phenomenon could accelerate the formation of a large number of heat-checking cracks.