Improved fatigue strength of Cr-electroplated 7075-T6 Al alloy by micro-shot peening

The effects of micro-shot peening (MSP) on the rotating bending fatigue resistance of Cr-electroplated AA 7075-T6 Al alloy were investigated. Fe-based amorphous particles with sizes of 50-80 mu m were used as the shot balls and peened under 100 % surface coverage. The shot-peen intensity, determined by the height of the N-type Almen specimen, was 0.110 mm. The Cr-electroplated layer consisted of a network of microcracks in the as -plated condition. Without the necessity of micro-crack initiation, the Cr-electroplated substrate had the short-est fatigue life and lowest fatigue strength among the tested samples. MSP significantly increased the fatigue strength/life of 7075-T6 Al alloy with or without Cr-plating. The introduction of high residual compressive stress combined with the formation of a nanograined structure in the MSP zone was responsible for the high resistance to fatigue crack growth of the MSP sample.