The effect of coarse intermetallic particles on the fracture process in forged 7000 alloys

The effect of coarse intermetallic particles on the fracture process in 7000 alloy forgings was investigated using three alloys with different (Fe + Si) impurity levels. The intermetallic particles were identified by selective etching and energy dispersive spectroscopy analysis conducted on a scanning electron microscope. Their geometrical parameters were estimated by image analysis and then correlated with area fractions of different fracture modes on the broken fracture toughness test specimens. It was found that the dominant fracture mode varies with the (Fe + Si) content. The coarse voiding at large intermetallic particles increases systematically with an increase of the impurity level, which in turn increases the amount and size of particles containing Fe and Si while decreasing their spacing. That the crack nucleation and propagation are accelerated by these particles was revealed by in situ scanning electron microscopy observation of the fracture process.