Lightweight and high-strength high-pressure die casting (HPDC) aluminum has been widely used in automotive components such as the cylinder block, lower crankcase extension, transmission case, and drive unit. Die cast parts have good surface finishes with relatively higher material strength in the casting skin than the center core material, maintain consistent features and tolerance, and maximize metal yield, therefore making it the most cost-effective casting process for mass production of aluminum parts. However, due to the rapid filling rates, the HPDC process tends to form large porosity and oxides because of the entrapped gas and solidification shrinkage, thereby deteriorating the mechanical properties of the casting parts. Water quenching has been widely used in the HPDC process to quench the castings after die ejection to increase material strength, hardness, and productivity; however, this process also induces high-tensile residual stress, which negatively affects the performance of the casting components in their design life.
In this study, a novel and industry-first analytical tool is presented, which incorporates the effects of both casting flaws on material strength as well as high residual stress induced by the water quenching process in HPDC aluminum block fatigue analysis. Furthermore, the application of this analytical tool is illustrated with a case study that addresses an aluminum bore wall crack of the HPDC block under a dynamometer durability test, as well as a design of experiment (DOE) study that optimizes the cylinder bore wall design to remedy this issue and make a robust block design.
