Effect of local microstructure on fatigue and related failure mechanisms in AlSi-castings

Mobility applications often demand shape-optimized designs. Casting of AlSi-alloys is an efficient bulk production technology featuring parts with strongly varying wall thickness. The local cooling rate is process controlled, implying severe changes in mechanical properties such as degree of porosity and secondary dendrite arm spacing. This study provides a brief overview about the effect of local microstructural properties, and intrinsic defect distribution, on associated fatigue strength for alloy EN AC 42100 and alloy 46200. Results from extensive fractographic investigations and computed tomography revealed microporosity as the primary failure mechanism for high-cycle-fatigue design, but dependent on the load level and casting process condition other crack initiating imperfections such as oxide films, slip planes and inclusions get more pronounced. A statistical assessment of fatigue strength considered the local manufacturing conditions and the associated varying failure mechanisms.