On the combined effects of surface quality and pore size on the fatigue life of Al-7Si-3Cu-Mg alloy castings

This study has aimed to determine the effects of surface quality and pore size, obtained by different levels of hydrogen content of the liquid metal, on the fatigue behavior of an Al-7%Si-3%Cu-Mg casting alloy. Three surface conditions have been studied: as-cast rough, as-cast smooth, and standard machined and polished surface. The S-N curves have shown that surface roughness and hydrogen content individually impact fatigue strength. Surprisingly, the fatigue strength of machined and polished samples, which aligns with standard testing practices, is significantly reduced, compared to other conditions. Fatigue cracks have been observed to initiate at the pores just below the as-cast surface or on the machined surfaces. In all cases, pores have been observed to be surrounded by bifilms. Moreover, hydrogen content and roughness of the as-cast surface have been found to interact to determine the fatigue performance. These findings necessitate a re-evaluation of fatigue testing procedures for cast aluminum components.