A relationship between fracture toughness or critical crack tip opening displacement (CTODc) and Fe-and Si-rich insoluble inclusions in 7000 type alloys was studied. The magnitude of crack tip plastic blunting or fracture toughness is determined by forming characteristic dimples just in advance of the stretched zone. The dimples on fracture surfaces are classified into two types of populations by scanning electron micrography and energy dispersion spectroscopy analysis.zone never exceed the average spacing of these inclusions. The characteristic dimples effective to determine CTODc are formed by the inclusions containing Fe or Si.
Effect of alloy purity and aging on the fracture toughness of three type alloys has been examined to clear the relationship between the fracture toughness and tensile properties. The fracture toughness were evaluated by the critical crack tip opening displacement (CTODc) derived from stretched zone analysis. The general magnitud of CTODc increases with reduction in iron and silicon contents. The value of CTODc depends on the aging condition. It lowers as the yield strength rises, or the value of the strain-hardening exponent decreases. All underaged alloys show a superior to toughness to the overaged of ones having the same yield strength. The total impurity content is, accordingly, a dominant fractor governing the fracture toughness of these alloys. The final values of fracture toughness were also determined by the tensile parameters, yield strength and strain-hardening exponent.Keysords: 7075 aluminum alloy, fracture toughness, tensile properties, critical crack tip opening displacement, effect of purity.
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