An experimental and numerical analysis of water jet peening of Al6061-T6

Water jet peening (WJP) is used to improve the fatigue life of materials by inducing compressive residual stress (RS) into the metal surface. In this paper, the formation mechanism of RS in a single pass WJP process and the coupling mechanism in the multiple passes WJP process are investigated. Then, simulations of single pass WJP are conducted to observe the transient evolution and steady distribution of RS. After that, the influences of process parameters (i.e., the distance between the center of adjacent water jets DC and jet velocity v) on the RS and surface roughness Ra are experimentally and numerically investigated after multiple passes WJP. Besides, the relationship between microhardness and plastic strain is also investigated. Finally, the fatigue performance is evaluated by the tension-tension fatigue tests. Results show that RS is mainly induced by the unrecovered elastic strain resulting from the obstruction of plastic strain. The value of the compressive RS, the depth of the compressive RS layer, and Ra all increase with an increase in v. The distribution of RS and the value of Ra will be affected by DC, the residual stress field (RSF) is uniform, and Ra is minimum for DC = 0.15 mm in this work. Taking RS and Ra into consideration, the optimal process parameters of v = 345 m s−1, DC = 0.15 mm, and jet traverse velocity vf = 4000 mm min−1 are eventually determined. Under this condition, the maximum compressive RS is − 156.7 MPa, the depth of the compressive RS layer is 220 μm, the surface microhardness is 106.7 HV0.1, and the Ra is 0.574 μm. Compared with the original specimens, the fatigue life of the peened specimens and the polished specimens after peening (Ra = 0.382 μm) increased by 53.2% and 90.8%, respectively.