Origin of Ductile Fracture in Aluminum Alloys

It is well known that metallic materials usually exhibit microvoid nucleation induced by particle fracture, followed by its growth and coalescence. Recently the present authors have revealed that hydrogen micropores play significant role in ductile fracture in AA2024 and AA5056 aluminum alloys, whereas the particle fracture mechanism operates only incidentally. The pre-existing hydrogen micropores exhibit premature growth under external loading before the maximum load, while particle fracture occurs after the maximum load. This tendency was accelerated in notched and cracked materials, because tri-axial stress state, which is necessary for isotropic growth of pores/voids, is generated ahead of a notch. According to the estimation on the areal fraction of dimple patterns originating from the pre-existing hydrogen micro pores, it has been concluded that the hydrogen micro pores make significant contributions to ordinary ductile fracture.