The influence of heat treatment and solidification time on the behavior of small-fatigue-cracks in a cast aluminum alloy

For a wide range of stress amplitudes, the fatigue life of cast aluminum specimens is dominated by propagation of small cracks that initiate predominantly from microshrinkage pores. Therefore, an understanding of the small-crack behavior and knowledge of the pore size distribution enables the prediction of fatigue properties. In order to understand the influence of processing parameters on fatigue performance, small-crack growth was monitored for three different solidification times in both peak-aged (T6) and over-aged (T7) conditions of cast W319 aluminum, a commercial Al–Si–Cu alloy used in automotive castings. Results indicate that small cracks in the T6 microstructures grow only slightly slower than those in the T7 material. A correlating parameter of the form [(εσ/σy)na] is shown to effectively characterize small-crack growth rates in both the T6 and T7 conditions for a wide range of applied stresses and solidification times.