Surface Finish Improvement of Selective Laser Melted Aluminium Alloy by Surface Mechanical Attrition Treatment

ABSTRACT: Surface mechanical attrition treatment (SMAT) has been used to treat the surfaces of an aluminium alloy manufactured by selective laser melting (SLM). SMAT involved impacting the SLM sample surface with spherical balls at a frequency of 30 Hz for 10 min to 30 min, which induced plastic deformation of the sample surface, leading to a change in surface finish and surface hardness. The surface finish, morphology, hardness, and structural features have been investigated. The results show that SMAT is very effective in improving the surface finish of the SLM aluminium alloy surface. After 30 min of treatment, the roughness value (R_a) was reduced by 87%, from 19.4 μm to 2.6 μm. SMAT also has the benefit of increasing the surface hardness of SLM aluminium alloy from 125 HV_0.1 to 160 HV_0.1, and generating a strain hardened layer of about 300 μm thick at the subsurface, and thus has the potential of improving wear resistance. In addition, SMAT induced a compressive residual stress of around 100 MPa on the treated surface, which would be beneficial in improving the fatigue properties of SLM aluminium alloy. The mechanisms underlying surface smoothing, hardness increase, and the evolution of compressive residual stress in SMAT are discussed in terms of severe surface plastic deformation and strain hardening.