Study On Fatigue Properties Of Wrought Al-12.7Si-0.7Mg Alloy

Material fatigue is one of the main performance indicators of components.As a new type of structural material,the fatigue properties of deformed Al-Si alloy in application need further study.In this paper,the samples were prepared in three states by DC casting of Al-12.7Si-0.7Mg alloy by hot extrusion deformation and solid solution at 520℃ for 90 min and subsequent treatment at 180℃ for 3 h.The static properties and fatigue properties of the alloy were studied by room temperature stretching and fatigue experiments,and the fatigue life curve of the alloy was obtained by means of "least square s" method.The conclusions are as follows:（1）The structure of extruded Al-12.7Si-0.7Mg alloy consists of a-Al matrix,fine silicon particles,Al₈FeMg₃Si₆ phase and Mg₂Si phase.The average size of silicon particles in extruded alloys is 2.7μm and the aspect ratio is 2.2.The ratio of length to width of silicon particles decreases after solution treatment,but the effect of aging treatment on silicon particles is not obvious.（2）The tensile and low stress fatigue properties of extruded Al-12.7Si-0.7Mg alloy are significantly higher than those of 6063 alloy.The tensile strength and fatigue life of wrought alloys increased significantly after heat treatment.The fatigue limit value of wrought alloy after aging treatment is the highest,that of extruded alloy is the lowest,and that of solid solution state is the middle.（3）The ductile fracture mechanism of extruded Al-12.7Si-0.7Mg alloy under tension is mainly due to the micro-pore aggregation fracture caused by the self-fracture of silicon particles.（4）The fatigue fracture of extruded Al-12.7Si-0.7Mg alloy consists of three parts:fatigue source zone,crack propagation zone and instantaneous fracture zone.The fatigue cracks are initiated on the surface of the specimens under different stress levels.There are a large number of fatigue steps in the crack propagation zone,and there are parallel fatigue stripes on the steps,and there are secondary cracks near the fatigue stripes at low stress level.The fracture morphology of instantaneous fracture zone is similar to that of tensile fracture zone and consists of a large number of dimples.