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    Assessing the efficacy of several impact-based mechanical techniques on fatigue behavior of additive manufactured AlSi10Mg
    (Elsevier Science Sa, 2023) Maleki, Erfan; Bagherifard, Sara; Unal, Okan; Shao, Shuai; Shamsaei, Nima; Guagliano, Mario
    Post-processing methods to reduce issues associated with the presence of internal and external anomalies are often necessary for obtaining adequate structural performance for additively manufactured products. However, the choice of the proper post-treatment and the corresponding parameters is still a challenge requiring adaption to the material type, geometry, size and undeniably costs. In this study, four different pure impact-based mechanical operations involving ultrasonic nanocrystal surface modification (UNSM), ultrasonic shot peening (USSP), severe shot peening (SSP), and severe vibratory peening (SVP) to investigate their efficacy on the fatigue behavior of hourglass AlSi10Mg specimens manufactured via laser powder bed fusion (LPBF) were considered. Experimental characterizations involving microstructural approach, porosity level and surface texture, hardness and residual stresses measurements, as well as tensile and fatigue testing, were conducted. The results exhibited considerable improvement in mechanical/physical performances leading to substantially enhanced fatigue performance of the mechanically treated specimens. Based on a cost-performance analysis, it was found that UNSM, while having reasonable cost, presented considerable improvement on fatigue behavior.
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    Effects of Laser Shock Peening on Corrosion Resistance of Additive Manufactured AlSi10Mg
    (Mdpi, 2023) Maleki, Erfan; Unal, Okan; Shao, Shuai; Shamsaei, Nima
    Mechanical properties of Al alloys make them an ideal candidate for different sections of marine, aerospace, automotive, etc. industries. Recently taking the advantages of additive manufacturing (AM), many complex infrastructures/components can be fabricated with very high design freedom via Al alloys. Although Al alloys have good natural corrosion resistance, however improving this property attracts lots of attention in the past few years. Post-processing methods can play a key role for addressing the issues related to internal and surface anomalies associated with as-built AM parts. Generally, these anomalies have detrimental effects on mechanical properties. In the present study, the effect of laser shock peening (LSP) treatment with different laser pulse overlaps and energies was investigated comprehensively on microstructure, surface texture, porosity, hardness, residual stresses as well as corrosion resistance of laser powder bed fused (L-PBF) AlSi10Mg samples. LSP provides strain deformation on the surface, and the deformation enhances by laser beam energy. LSP1 (laser energy of 1.5 J and 50% overlap) and LSP3 (laser energy of 4.5 J and 50% overlap) introduce maximum local strain of 7.5 and 10.7, respectively. The surface roughness of as-built state mu m in terms of Rv was effectively diminished to 16.33 after LSP6 (laser energy of 4.5 J and 75% overlap). The results indicated that due to the modified surface texture, improved hardness and induced high compressive residual stresses in the surface layer. (surface hardness improvement and inducing high surface compressive residual stresses were obtained after LSP6 up to 26% and 289 MPa, respectively); the LSP treated samples exhibited higher corrosion resistance with the corrosion rate decreasing down to 50% as compared to the as-built state.
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    Fatigue performance of U-notched additively manufactured AlSi10Mg parts: The effects of chemical and thermal post-treatments
    (Elsevier, 2023) Maleki, Erfan; Bagherifard, Sara; Ahmad, Nabeel; Shao, Shuai; Unal, Okan; Guagliano, Mario; Shamsaei, Nima
    In the current study, the effects of different post-processing methods, including heat treatment (HT) and electrochemical polishing (ECP) as well as their combination on the surface texture, porosity, microstructure, mechanical properties, and rotating bending fatigue behavior of U-notched laser powder bed fused AlSi10Mg specimens were comprehensively investigated. In addition, to better understand the effects of the applied post processing methods on the sensitivity of the notched specimen to surface and near-surface defects, finite element analysis was performed. Chemical treatment was found to be very influential on surface texture modification of the very narrow notched parts, for which the application of other treatments can be quite challenging. It was also found that the fatigue behavior of the notched specimens was more sensitive to the surface texture rather than to the near-surface defects. The hybrid treatment involving HT+ECP was the most effective for fatigue behavior improvement due to simultaneous homogenization of the microstructure, released tensile residual stresses, enhanced ductility and high surface texture modification.
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    Superior effects of hybrid laser shock peening and ultrasonic nanocrystalline surface modification on fatigue behavior of additive manufactured AlSi10Mg
    (Elsevier Science Sa, 2023) Maleki, Erfan; Bagherifard, Sara; Unal, Okan; Jam, Alireza; Shao, Shuai; Guagliano, Mario; Shamsaei, Nima
    The surface texture of metallic parts produced by laser powder bed fusion (L-PBF) in the as-built condition detrimentally affects their mechanical properties, especially fatigue behavior. Accordingly, applying surface post-treatments has become an attractive approach to improve the mechanical performance of these materials. In the present study, both the individual and combined effects of post-processing methods, i.e., laser shock peening (LSP) and ultrasonic nanocrystalline surface modification (UNSM) with the same intensity of 10-12 A [0.001 in.], were systematically investigated on mechanical properties and fatigue behavior of L-PBF AlSi10Mg speci-mens. A wide range of experiments involving microstructural characterization, hardness and residual stresses measurements, porosity and surface texture analyses, tensile tests, and rotating bending fatigue tests were conducted. The results revealed that the hybrid LSP + UNSM process resulted in significant improvement in mechanical properties and fatigue behavior due to (i) sub-surface pores closure up to the depth of 517 mu m, (ii) 60 % surface hardness improvement, (iii) inducing-420 MPa surface compressive residual stresses, and (iv) surface roughness reduction up to 70 %. The fatigue life was improved up to 75, 56, and 35-fold compared to the as-built state after applying LSP + UNSM, UNSM, and LSP treatments, respectively.