Novel quantification of porosity defects on fatigue behavior for cast aluminum-silicon alloys by X-ray micro-tomography

Casting pores, as inevitable microscopic defects in castings, usually have a significant influence on the mechanical properties of materials, especially the fatigue properties. In this study, high cycle fatigue (HCF) tests for smooth specimens made of cast AlSi7Mg1 alloy (close to ASTM A357) with casting pores are performed. X-ray micro-tomography is used to obtain the 3D information of pores and cracks. The experimental logarithmic fatigue life is found to have a linear relation with the equivalent size and relative location of the critical pore. In addition, locally concave or convex areas on crack surfaces are discovered and the formation mechanism is identified. Based on a continuum damage mechanics (CDM) based HCF damage evolution equation, a pore-sensitive fatigue model is proposed by considering the size and location of pores in 3D. The test results and calculation results show that the developed pore-sensitive fatigue model can accurately predict the fatigue life.