Low-cycle Fatigue Behavior Of Extruded Al-0.8%Mg-0.6%Si-xSc Alloy

Aluminum alloys are concerned by more and more people due to its excellent properties, and have been widely applied in aeronautics and astronauts, automobile industries, etc. For further improvement of the properties of aluminum alloys, expanding the applied scope of aluminum alloys, rare earth element Sc has been choosen as the alloying element added into the aluminum alloy, the effect of trace Sc and solution plus aging (T6) treatment on the fatigue deformation behavior are investigated.According to the composition of the alloys, Al-0.8%Mg-0.6%Si-x%Sc are melted, then by casting, extrusion, finally fatigue samples needed are fabricated, T6 treatment was taken on partial samples, then the observations on the microstructures and fatigue tests are performed. The microstructure observations show that the microstructures of the extruded Al-0.8%Mg-0.6%Si-x%Sc alloys can be refined effectively with certain Sc, after T6 treatment, grain size of the alloys decreased apparently except for the alloy with 0.2%Sc which changed a little. The results of low-cycle fatigue tests reveal that the as-extruded (F) Al-0.8%Mg-0.6%Si-x%Sc alloys exhibit the cyclic strain hardening, degree of cyclic strain hardening mainly depends on the content of Sc and imposed total strain amplitude, extruded Al-0.8%Mg-0.6%Si-x%Sc alloys at T6 state exhibit the cyclic strain hardening, cyclic strain softening, cyclic stability. For the extruded Al-0.8%Mg-0.6%Si-x%Sc alloys at F and T6 state, the relationship between plastic and elastic strain amplitudes with reversals to failure shows linear behavior, and can be well described by the Coffin-Manson and Basquin equations, and for the extruded Al-0.8%Mg-0.6%Si-0.2%Sc alloy after T6 treatment, the relationship between plastic strain amplitude and reversals to failure shows bilinear behavior. The observations on the fracture surfaces of fatigued specimens reveal that under the condition of fatigue loading, the fatigue cracks initiate in a transgranular mode at the surface of fatigue specimens, and propagate transgranularly for extruded Al-0.8%Mg-0.6%Si-x%Sc alloys at F and T6 state.