Detection and influence of shrinkage pores and non-metallic inclusions on fatigue life of cast aluminum alloys

In this work, test bars of cast aluminum alloys EN AC-AlSi8Cu3 and EN AC-AlSi7Mg0.3 were produced with a defined amount of shrinkage pores and oxides. For this purpose a permanent mold with heating and cooling devices for the generation of pores was constructed. The oxides were produced by a contamination of the melt. The specimens and their corresponding defect distributions were examined and quantified by X-Ray computer tomography (CT) and quantitative metallography respectively. A special test algorithm for the simultaneous image analysis of pores and oxides was developed. The defective samples were examined by fatigue testing. The presence of shrinkage pores causes a lowering of the fatigue strength. The results show that pore volume is not sufficient to characterize the influence of shrinkage pores on fatigue life. A parametric model for the calculation of fatigue life based on the pore parameters obtained from CT scans was implemented. The model accounts for the c ombined impact of pore location, size and shape on fatigue life reduction.