PSI - Issue 51

Lucia Pastierovičová et al. / Procedia Structural Integrity 51 (2023) 135 – 140 L. Pastierovi č ová et al. / Structural Integrity Procedia 00 (2022) 000–000

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Fig. 5. Detailed fatigue fracture surface of the alloy A (0.128 % Fe) at σ a = 78 MPa, (a) fatigue area near pores (b) final fracture, SEM.

The character of final fracture area is related to the morphology and size of the eutectic silicon and intermetallic phases present in the structure, see Fig. 5a. In all experimental alloys, transcrystalline ductile fracture of Al matrix with dimple morphology with local occurrence of cleavage facets (Fe-rich phase) was observed in the final fracture. The shape of the dimples is related to the shape of the silicon particles therefore the oval shape dimples are observed in Fig. 5b. On the other hand, higher initiation cracks were observed on the fatigue fracture surfaces of the specimens after simultaneous fatigue testing in a corrosive environment, see Fig. 6. As Fe increased, the number of crack initiation sites increased again. The character of the fatigue fracture and the final fracture area fully correlates with fatigue testing in a non-chloride environment. Casting defects such as porosity and shrinkage were identified as the crack initiation sites. However, on the inner parts of the casting defects, the typical smooth surface was not observed due to the presence of corrosion products documented in Fig. 7.

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Fig. 6. Macroscopic view of fatigue fracture surfaces of alloy A (0.128 % Fe); (a) σ a = 68 MPa; (b) σ a = 78 MPa; (c) σ a = 88 MPa, SEM.