Enhancing surface layer properties of an aircraft aluminum alloy by shot peening using response surface methodology

• Effects of 4 parameters on hardness and residual stress are examined based on Box–Behnken design.
• Optimal peening conditions are obtained by using desirability function approach.
• Surface layer properties are verified at the optimal conditions.

Shot peening leads to local plastic deformations in the near-surface regions, which result in the development of residual stress and the improvement of surface hardness in the aerospace structural components. These properties can be enhanced by careful selection of the peening parameters. 2124-T851 aluminum alloy is widely used in the aerospace industry due to its high specific static strength. In this study, a response surface methodology is presented to optimize the surface properties of microhardness and residual stress. The effects of four peening parameters (nozzle distance, pressure, impact angle, and exposure time) on microhardness and residual stress are investigated. Box–Behnken design, a popular second-order response surface design, is employed to systematically estimate the empirical models of microhardness and residual stress in terms of the four parameters. Based on the estimated models, optimum peening conditions are recommended by using the desirability function approach, which is the most popular technique for optimizing multiple responses. Additionally, to verify the validity of the optimal conditions obtained from experimental results, metallurgical analyses of the shot-peened aluminum alloy were conducted with respect to hardness, residual stress, surface morphology, X-ray diffraction analysis, and surface roughness.

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