Relationship between fracture toughness and tensile properties in Al-Zn-Mg-Cu alloys.

Abstract

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.

Aging of a copper bearing HSLA-100 steel

“…Mujahid et al (1998), Wilson et al (1988), Dhua et al (2001) and Hamano (1993) also observed similar dips in the CVN values in peak aged condition in their studies on HSLA steels. There have been various attempts to study the causes of poor impact strength in peak aged alloys (Sanders and Starke 1982;Duerig et al 1985;Higashi et al 1985). According to Hamano (1993) and Skoufari et al (1999), poor ductility and impact strength are due to existence of coherent precipitates in peak aged condition.…”

“…For development of high strength materials possessing reasonable toughness, it is important to understand the effect of precipitate phases on plastic deformation behaviour. For example, several age hardenable high strength materials show the lowest toughness and the maximum strength in the peak-aged condition (Higashi et al 1985). The coherent precipitates are easily cut by moving dislocations (Sanders and Starke 1982;Duerig et al 1985;Higashi et al 1985;Hamano 1993), which leads to inhomogeneous deformation, early crack initiation, and poor toughness.…”

“…For example, several age hardenable high strength materials show the lowest toughness and the maximum strength in the peak-aged condition (Higashi et al 1985). The coherent precipitates are easily cut by moving dislocations (Sanders and Starke 1982;Duerig et al 1985;Higashi et al 1985;Hamano 1993), which leads to inhomogeneous deformation, early crack initiation, and poor toughness. In the over aged condition, the strengthening precipitates are incoherent and can be bypassed by dislocations leading to homogeneous deformation and increasing toughness with delayed crack initiation.…”