Effects of Mg content on fatigue behavior of wrought Al–8Si–(0.33–1.32)Mg alloy sheets in T4 temper

Abstract

In this paper, microstructure, fatigue life and fatigue fracture behavior of Al–8Si–(0.33–1.32)Mg (mass fraction, %) alloy sheets in T4 temper were systematically investigated by scanning electron microscopy/energy dispersive spectroscopy, electron backscatter diffraction, transmission electron microscopy and high frequency fatigue tests. The results show that when the stress ratio R = 0 and the stress level is 165 MPa, the fatigue properties of Al–8Si–(0.33–1.32)Mg alloy sheets in T4 temper first increase and then decrease with the increase of Mg content. When the Mg content is 0.78 %–0.99 %, the fatigue life is the longest, reaching 7.14 × 10⁵∼2.99 × 10⁶ cycles. Fatigue cracks of Al–8Si–(0.33–0.99)Mg alloy sheets in T4 temper initiate at the persistent slip band. The fatigue crack initiation of Al–8Si–1.32Mg alloy sheet initiates at particles-associated aggregation area (PAA), and the fatigue initiation life of Al–8Si–1.32Mg alloy sheet is significantly shortened. PAA has little effect on tensile properties, but significant effect on fatigue properties. PAA can be regarded as a special defect affecting fatigue properties of materials. The stress concentration is the largest at particle orientation 0°. In addition, the smaller the particle spacing, the greater the stress concentration, the easier the crack initiation under applied load, when the particle spacing is greater than one particle spacing, the particle aggregation effect disappears. This study optimizes the fatigue behavior of high-silicon wrought aluminum alloy by controlling the Mg content and discovers a novel fatigue defect (PAA), providing important scientific insights for optimizing alloy properties and meeting diverse industrial needs.