Advanced Characterization of the Cyclic Deformation and Damage Behavior of Al-Si-Mg Cast Alloys Using Hysteresis Analysis and Alternating Current Potential Drop Method

The demand for lightweight and fatigue-resistant solutions in the automotive and aerospace industries requires the extensive use of light metals like Al-Si-Mg aluminum cast alloys. To ensure a safe design for fatigue-loaded aluminum cast components, the relation between microstructure characteristics of α-Al dendrites (e.g. dendrite arm spacing, microhardness) and interdendritic Al-Si eutectic (e.g. Si eutectic morphology), stress-strain behavior and fatigue lifetime including the number of cycles to crack initiation and crack propagation behavior has to be understood. For this purpose, fatigue tests in the LCF and HCF regime from 1E2 to 1E7 cycles were performed for aluminum cast alloy EN AC-AlSi7Mg0.3. With this, the effect of α-Al microhardness and Si eutectic morphology was investigated on monotonic and cyclic stress-strain behavior by performing tensile, incremental step (IST) and constant amplitude tests (CAT) in the LCF regime. Moreover, microstructure-specific S-N curves were determined in the HCF regime until 1E7 using online hysteresis analysis and alternating current potential drop (ACPD) method for monitoring the deformation and damage evolution. Hereby, computed tomography (CT) analyses were used to evaluate the damage state intermittent and post-mortem in CAT. As a result, ACPD method could be validated as a sensitive and reliable technique for quantitative characterization of stress- and cycle-dependent deformation and damage behavior including cyclic hardening, softening and saturation as well as crack initiation and propagation until failure.