Fracture Toughness And Fatigue Crack Growth Of Al-Mg-Sc Alloy

Abstract:The fracture toughness and fatigue crack growth experiments of L-T and T-L orientation Al-Mg-Sc alloy were conducted. The fracture toughness and fatigue crack growth behavior was investigated by optical microscopy(OM), Scanning electron microscopy (SEM) and other methods, and gets following conclusions:(1) Orientions affect the fracture toughness of Al-Mg-Sc alloy to some extent. Kc of L-T orientation is slitghly higher than the T-L orientation, fracture surface presents typical ductile dimple morphology.(2) The da/dN-△K curve of Al-Mg-Sc alloy conforms to the Paris law, shows the typical FCG three stages:slow propagation stage, stable propagation stage and fast propagation stage, Orientions of Al-Mg-Sc alloy plate has little influence on fatigue crack growth rate.(3) Under the condition of highr stress ratio, fatigue crack propagation of Al-Mg-Sc alloy begins at lower△K, propagation stage is narrow and fast propagation begins at a much lower△K. With the same△K value, the fracture surface is of relatively higher roughness, even more tortuous crack path, and higher fatigue crack growth rate under higher stress ratio condition.(4) In FCG first stage, fatigue crack tends to propagate along the grain boundary in Al-Mg-Sc alloy. With△K value increases, propagation of the fatigue crack becomes insensitive to the grain size. In FCG second stage, the mode of fatigue fracture gradually transforms to transgranular fracture, Delamination in fracture suface decreases, crack path becomes rougher, some typical fatigue damage characteristics are found at fast propagation zone such as fatigue stripe, dimples.