Study on surface properties and fatigue performance of aluminum alloy plate with prestressed ultrasonic peening

Prestressed ultrasonic peening (UP) is beneficial to enlarge bending deformation and improve surface properties of the plate compared to free UP process. The effects of processing parameters on variation of surface topography, surface roughness and hardness, residual stress distribution are analyzed. Then the microstructure and fatigue life with prestressed UP is studied. The results show that smaller surface roughness, larger surface hardness, larger and deeper compressive residual stress are generated in prestressed UP compared to free UP. Small prebending curvature radius and offset distance both contribute to enhancement of surface properties. Large firing pin velocity is beneficial for large surface hardness as well as larger and deeper compressive residual stress; nevertheless, it will increase the surface roughness. The UP process mainly improves the high cycle fatigue life of the material, while there is no difference of the low cycle fatigue life between the peened and un-peened samples. The high cycle fatigue life significantly increases at small stress after peening process and it can be further enhanced after prestressed UP. Deformation band with peened indentations are generated on the surface. With the experiments of distributions for hardness, yield stress and residual stress, the strengthening mechanism in peening process is discussed.