Abstract
In this paper, the effect of two-step aging treatment on microstructure and fracture toughness of 7085 aluminum alloy were investigated by using tear tests to carry out the fracture toughness tests of the alloy and using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to analyze the microstructure. The results showed the main precipitates in the alloy were GP zones and η' phases in the grains after 118°C/6h aging treatment. With further secondary aging treatment, grain boundaries precipitates (GBPs) grew up, and the precipitate-free zone (PFZ) showed up, the increasing proportion of intergranular failure was occurred and the fracture toughness decreased. With further prolonging of the secondary aging treatment time, precipitates in the grains tended to be coarser, the GBPs became discontinuous ,PFZ became wider, and there were decreasing proportion of the intergranular failure and increasing proportion of the transgranular failure showing on the fracture morphologies, the fracture toughness of 7085 aluminum alloy increased.
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