Analysis on the Fatigue Properties of Shot-Peened Al-Si-Mg Alloy and Its Fatigue Life Prediction
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JMEPEG https://doi.org/10.1007/s11665-020-05001-7
Analysis on the Fatigue Properties of Shot-Peened Al-Si-Mg Alloy and Its Fatigue Life Prediction Kaixin Su, Jiwang Zhang, Hang Li, Mingze Wu, Shoudong Zhu, Kejian Yi, and Jinxin Zhang (Submitted February 20, 2020; in revised form July 8, 2020) Ceramic micro-shot peening (CMSP) and steel micro-shot peening (SMSP) were utilized to investigate the effect of micro-shot peening (MSP) on the high-cycle fatigue properties of Al-7Si-0.3Mg casting aluminum alloy in a previous study. However, the improvement effects of CMSP and SMSP on the fatigue strength (at 5 3 107 cycles) were only 33% because the depth of harden layers was only 20 and 55 lm while the depth of compressive residual stress affected layers was only 37 and 68 lm. In this study, conventional shot peening (CSP) was utilized, and the results were compared with those of MSP, with the expectation that CSP would provide a greater improvement in the fatigue strength. The affected surface layers of the shotpeened specimens were characterized using surface morphology, microhardness, and residual stress analyses. In addition, the effect of CSP on the fatigue strength at 5 3 107 cycles was investigated using a rotating bending fatigue test (R = 2 1). An investigation of the extensive surface compressive residual stress relaxation process for the three different shot-peened specimens during cyclic loading was conducted using x-ray diffraction. In addition, the initiation sites for fatigue cracks on the fracture surface were observed using scanning electron microscopy. Furthermore, the fatigue life of the samples with the internal casting defect failure mode was predicted using linear elastic fracture mechanics, while that for samples with the surface crack initiation failure mode was predicted using the modiļ¬ed Morrow model considering the residual stress. Keywords
Al-7Si-0.3Mg, casting defects, fatigue mechanism, life prediction, shot peening
fracture
1. Introduction Al-7Si-0.3Mg casting aluminum alloy has been widely used in high-speed railway catenary positioning devices because of its good mechanical properties, castability, and corrosion resistance (Ref 1). Recently, as a result of the increasing speed of high-speed trains, the fatigue performance requirements for high-speed railway catenary positioning devices have also increased. Therefore, surface strengthening treatments, which are effective methods to improve the fatigue resistance of metallic materials, are widely applied to aluminum alloys to improve their fatigue performances (Ref 2-12). Shot peening is one of the most widely used methods for mechanical surface strengthening treatment. In this method, the surface of a material or component is repeatedly bombarded by accelerated particles, which cause severe plastic deformation of the surface layer. This introduces work hardening and compressive residual stress on the substrate surface, which effectively improves the fatigue performance of the material or component. The effect of shot peening on the fatig
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