EFFECT OF SURFACE LASER SHOCK PEENING ON THE TENSILE PROPERTIES AND HARDNESS OF SELECTIVE LASER MELTED (SLMed) A357 ALLOY

Ignatius Uyabemem Agbaye; Tuty Asma Abu Bakar; Aini Zuhra Abdul Kadir

Ignatius Uyabemem Agbaye Department of Metalworks Technology Education, School of Technical Education, Federal College of Education (Technical), Asaba, Delta State, Nigeria.
Tuty Asma Abu Bakar Materials Research and Consultancy Group (MRCG), Department of Mechanical Engineering, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia.
Aini Zuhra Abdul Kadir Department of Materials and Industrial Engineering, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia.

Keywords: Laser shock peening, selective laser melting, residual stress, aluminium alloys

Abstract

Selective laser melting (SLM) has been widely used to fabricate Al-Si-Mg alloys, which are extensively used in the automotive, aerospace, and biomedical industries. However, due to its rapid solidification and cooling rates, the process induces thermal fluctuations that lead to residual stresses in the parts, necessitating stress-relief post-processing. This study examines the influence of surface laser shock peening (LSP) on the residual stress profile, microstructure, hardness and tensile properties of A357 alloy fabricated by SLM. LSP treatment was done using controlled laser parameters and dimple spacing. X-ray diffraction analysis shows that compressive residual stresses up to -57 MPa were produced, which modified the tensile residual stresses (TRS). Variable pressure scanning electron microscopy (VP-SEM) revealed remarkable grain refinement and a uniform distribution of primary α-Al and fibrous Si phases after LSP, which is attributed to LSP-induced plastic deformation and a high dislocation density. This produced an improvement of about 18.6 % in hardness. Mechanical tests recorded improvement in strength, as yield strength (YS) increased from 87±0.87 to 155±1.32 MPa, about 78 % increase, while ultimate tensile strength (UTS) increased from 197±1.0 MPa to 263±3.61 MPa, representing 33.4 % increase at the bottom of the sample. At the sample top, YS increased from 95±1.0 MPa to 171±2.65 MPa, a 80 % increase, while the UTS increased from 200±2.65 MPa to 269±2.65 MPa, representing 34.5 % increase. However, elongation decreased slightly due to strain hardening. Analysis of fractured surfaces reveals reduced porosity and defect closure in the LSP-treated samples, which inhibited crack initiation and propagation. This confirms that LSP is an effective strategy for mitigating residual stresses and improving the mechanical performance of the A357 alloy, making it appropriate for critical structural applications.