Effect of Shrinkage Versus Hydrogen Pores on Fatigue Life of Cast AlSi11Mg Alloy

Shrinkage pores in cast aluminum components are often the reason for premature failure during cyclic loading due to their large size and fissured morphology. Complete avoidance is technically not possible due to processing constraints, but shrinkage pores can be substituted by significantly smaller and spherical gas pores by means of controlled hydrogen upgassing. The newly developed and simulation-optimized casting system enables precise and reproducible casting of various pore distributions, which have been extensively characterized. Correlations between shrinkage vs. hydrogen pores and fatigue behavior were quantified concerning very high cycle fatigue and crack propagation behavior as well as analyzed by 3D µ-CT to identify the failure mechanisms. In the as-cast condition, fissured shrinkage pores, especially near the surface, lead to crack initiation and premature fatigue failure. The strong scattering of fatigue life can be significantly reduced by the controlled insertion of hydrogen pores. Furthermore, the experimental studies indicate that hydrogen pores increase the critical crack growth threshold and reduce the crack propagation rate by crack deflection, crack splitting and crack tip blunting.