Improving fatigue behaviour of additively manufactured Scalmalloy® using laser shock peening

Scalmalloy®, an Al-Mg-Sc based alloy tailored for additive manufacturing, is increasingly used in aerospace and high-performance engineering applications due to its high specific strength, stiffness and comparable density as other aluminum alloys. However, fatigue performance of as-built Scalmalloy® parts could deteriorate rapidly due to its heterogeneous microstructure and inherent surface defects. While heat treatments are commonly employed to enhance its properties, there is an opportunity to enhance the properties further using mechanical surface treatments such as laser shock peening (LSP). This study examines the impact of LSP with a pulse energy as low as 2.4 mJ on the microstructure and fatigue behavior of laser powder bed fusion (L-PBF) Scalmalloy®. Cross-sectional analyses revealed LSP reduced grain size near the surface from ∼4.0 μm to ∼2.8 μm and increased the geometrically necessary dislocation (GND) density by almost 1.5 times. Maximum compressive residual stress (CRS) close to 500 MPa was introduced on the top surface and compression penetrated to a depth of 250 μm. These microstructural modifications and CRS contribute to fatigue limit increment from 100 MPa to 175 MPa. The findings underscore the effectiveness of LSP as a post-processing technique for Scalmalloy® offering a viable pathway to improve the durability of critical aeronautics and space components operating under cyclic loading conditions. • Laser shock peening (LSP) increased fatigue strength of laser powder-bed fusion Scalmalloy®. • LSP with low pulse energy of 2.4 mJ yielded 250 μm depth of compressive residual stresses. • Surface morphological changes after LSP had negligible effect on fatigue behaviour. • LSP reduced grain size and increased hardness by ∼23% than un-peened microstructure.