Characterization of fracture path and its relationship with microstructure and fracture toughness of aluminum alloy 7050.

摘要

Al-Zn-Mg-Cu based wrought alloys are extensively used in structural applications where fracture toughness and yield strength are important parameters. Commercial hot-rolled and precipitation hardened Al-Zn-Mg-Cu based alloys, such as aluminum alloy 7050, are often partially recrystallized. It is well known that recrystallization adversely affects the fracture toughness of such alloys. However, in commercial practice, it is not usually possible to avoid partial recrystallization during processing of these alloys. Therefore, understanding of the effect of the attributes of partially recrystallized microstructure on fracture toughness of alloys such as aluminum alloy 7050 is of practical importance.; The present investigation is an in depth study of the effect of the characteristics of partially recrystallized microstructure on the fracture toughness and fracture surface morphology of aluminum alloy 7050. The emphasis is on the development of quantitative relationships among microstructural parameters, fracture surface morphology, and fracture toughness. Quantitative fractographic and stereological techniques are utilized for unbiased quantitative characterization of microstructure and fracture surfaces.; A new multiple micro-mechanisms based model is developed to relate fracture toughness of partially recrystallized 7050 alloy to the fracture surface morphology. The model is verified by using the quantitative fractograghic data on the fracture surfaces of the fracture-toughness test specimens. The fracture model is utilized to develop a model-based quantitative relationship between fracture toughness and microstructural attributes of the partially recrystallized alloy. The model predicts the dependence of fracture toughness on a number of microstructural parameters, and it also predicts the orientation dependence of the fracture toughness. It is shown that for peak-aged 7050 alloy, fracture toughness depends significantly on the degree of recrystallization, and a number of other parameters such as average size of recrystallized grains, and average thickness of recrystallized regions. Therefore, it should be possible to increase the fracture toughness of partially recrystallized peak-aged aluminum alloy 7050 alloy having a given degree of recrystallization by optimizing other microstructural attributes of the partially recrystallized microstructure such as average grain size and average thickness of recrystallized regions.