Low Cycle and Multiaxial Fatigue Behavior of Three Al-Mg-Si Alloys

Al-Mg-Si alloys (6xxx series) are medium strength structural alloys, with good corrosion resistance, good weldability and high damping capacity. They represent a high volumetric fraction of extruded aluminium alloys which are produced for commercial use and have been increasingly applied in the automotive industry. For structural materials, the fatigue strength is the most important factor to ensure a long-term reliability. Engineering structures such as aircrafts and automobiles usually undergo complex multiaxial loadings, which lead to changes of the principal stresses and strains directions in components during a loading cycle. In this study, fatigue tests were performed in three Al-Mg-Si alloys, namely AA 6005, AA 6351 and AA 6063, tempered and aged for the T6 condition. A comparative study was undertaken by assessing their Low Cycle Fatigue (LCF) properties and multiaxial fatigue behaviour using round smooth specimens. Strain-controlled fully reversed axial loadings and distinct combinations of axial-torsional fully reversed stress cycles, including in-phase and 90 out-of-phase loadings were adopted for the tests. The collected data are discussed in relation to some well-known multiaxial fatigue models.