Equal-channel angular pressing influencing the mean stress sensitivity in the high cycle fatigue regime of the 6082 aluminum alloy

The high cycle fatigue (HCF) behavior is investigated for a 6082 aluminum alloy in an as-extruded peak-aged condition and after single-pass equal-channel angular pressing (ECAP). The focus of this study is on the effect, that ECAP processing exerts on the mean stress sensitivity of the fatigue strength. The fatigue strength at 107 cycles is compared for alternating tension-compression (R = -1), tension (R = 0) and tension-tension loading (R = 0.1) and related to the microstructural features examined by electron backscatter diffraction (EBSD) measurements and the mechanical properties determined by quasi-static tensile and compression tests. For the as-extruded peak-aged alloy, the fatigue strength depends on the stress ratio. An increase in mean stress due to a higher applied stress ratio leads to decreased fatigue strength. Single-pass ECAP enhances the fatigue strength for all stress ratios when compared to the as-extruded peak-aged alloy. Furthermore, the mean stress effect is diminished and the fatigue strength is almost the same for the tested stress ratios. The mean stress insensitive behavior of the ECAP processed condition is most likely a result of an increased sensitivity to compression loading, which is caused by the ECAP induced shear-deformation and expresses further in a minor yield strength under compression loading when compared to the as-extruded peak-aged alloy.