Effect of shot peening forming and shot peening strengthening post-treatment on the fatigue behavior of bolt-connected 2024HDT alloy

To improve surface integrity and suppress fretting fatigue of bolt-connected 2024HDT alloy plate-hole structure, the effect of shot peening forming (SPF) and shot peening strengthening (SPS) post-treatment on the surface integrity and fatigue behavior of 2024HDT alloy was investigated. The results showed that the SPF treatment increased the fretting fatigue resistance of the 2024HDT alloy plate-hole structure, and the failure mode changed from fretting fatigue to plain fatigue. The SPS post-treatment with three different intensities investigated here all improved the plain fatigue resistance of the SPF sample, whose failure mode also manifested as plain fatigue. This was due to the SPS treatment that flattened the surface of the SPF sample and introduced a compressive residual stress (CRS) field with a larger value and deeper distribution, while increasing the dislocation density and hardness of the SPF sample, which suppressed the initiation and propagation of fatigue cracks. SPS with a medium intensity produced an excellent surface CRS field with the lowest roughness and slightest surface damage, resulting in an improved plain fatigue resistance of 7.92%.