Effect of chemical milling on low-cycle fatigue behavior of an Al–Mg–Si alloy

The effect of alkaline chemical milling used for dimensionally reducing aluminum-alloy structures is assessed in terms of total fatigue life and crack-initiation mechanisms. Chemically milled Al–Mg–Si specimens exhibited a 50% reduction in average fatigue lives compared to electropolished Al–Mg–Si specimens at comparable peak-applied loads above macroscopic yield. The fatigue-life reduction of the chemically milled specimens is likely associated with early onset of crack initiation due to pit-induced-stress concentrations. Fractographic analyses suggest a transition in the crack-initiation mechanisms from predominantly {1 1 1}-slip plane cracking to partly or predominantly pit-induced-stress driven depending on the depth of surface pits.

► Al–Mg–Si specimens milled in alkaline solution were subjected to low-cycle fatigue. ► The effect of chemical milling on crack initiation and fatigue life was assessed. ► Average fatigue life was reduced by 50% compared to electropolished specimens. ► Crack initiation occurred by pit-induced stress and/or crystallographic slip. ► The mechanisms of crack initiation depended on the existence/depth of surface pits.