Characteristics of Fatigue Fractures in Al-Si Cast Components
A well-established knowledge of the fractographic characteristics of cast alloys is required to perform fracture analysis of failed components and to determine their fracture mechanisms. It can also be used to validate related claims on car insurance coverages. These analyses contribute to the continuous improvement of the production process and product design.
This paper presents typical macrofractographic and microfractographic aspects of fatigue failures of cast aluminum components. As introduction, the general aspects of fatigue fractography and some examples of fatigue failures in aluminum cast components are presented. The examples of fatigue failures emphasize the microfractographics aspects and their relationship with microstructures of alloys.
In addition to the traditional beach marks on the fracture surface, the fatigue fractures in cast aluminum components show two relevant microfractographic aspects: the presence of tear ridges on the crack propagation direction and fatigue striations in the direction perpendicular to the crack propagation.
The tear ridges presence is independent of alloy microstructures, but the fatigue striations are directly related to aluminum dendrite volume fraction in the microstructure. The clear observations of the fatigue striations are restricted to the aluminum dendrite regions.