Abstract: Contributions of weak grain boundary,cracking path deflection and grain boundary delamination to fracture toughness anisotropy of high strength Al alloys were evaluated based upon approaches of fracture mechanics in conjunction with physical cracking mechanisms. The predicted results are close to those experimentally determined in the literature and in this work.The strong anisotropy of fracture toughness of high strength Al alloys is therefore attri- buted mainly to weak grain boundary cracking,cracking path deflection and grain boundary detamination.With the methods of this work,short-transverse fracture toughness values of some semi-products can he estimated from in-plane toughness values and corresponding frac- ture characteristics when it is difficult to be determined experimentally.

Key words: Al alloy, fracture toughness, anisotropy