Effect of Shot and Laser Peening on Fatigue Strength of Additively Manufactured Aluminum Alloy with Rough Surfaces

The effects of shot peening (SP) and laser peening (LP) on the fatigue strength of additively manufactured (AM) aluminum alloy (AlSi12) specimens with rough surfaces (labeled as-built specimens) were examined. Plane bending fatigue tests were conducted, and the fracture surface was observed. Distributions of the residual stress and hardness from the surface to the depth direction were obtained. The fatigue strengths of the as-built specimens subjected to SP (as-built + SP) and LP (as-built + LP) at 10 7 cycles were 59 and 76% higher than that of the as-built specimen, respectively. The surface roughness and waviness decreased and increased when the as-built specimen was subjected to SP and LP, respectively. Fatigue cracks originated from defects near the surface for the specimen without any surface roughness and concave areas on the surface for the as-built, as-built + SP, and as-built + LP specimens. The as-built + SP and as-built + LP specimens exhibited compressive residual stress, owing to which, the surface roughness did not considerably influence the fatigue strength. The integral values of the compressive residual stress ( S T ) near the surface were of significance in enhancing the fatigue strength of AM aluminum alloy. Specifically, the introduction of deep compressive residual stress near the surface by LP can help increase the fatigue strength.