Abstract: Filtering affects solid-solid and solid-Liquid phase transition of alluminum alloys. The common mechanical properties and crack roughness of the alloys, both in casted state and in deformed state, are improved, and the properties are made much more stable. The mechanism is that the solidification processing is affected by filtering so that the porosity in the alloy is reduced, its density both in casted and in deformed state is increased and ageohardening is a affected also. The particles in the centres of dimples on the crack surface are mainly precipitated phases and brittle compound phases comprised of impurities. The conclusion drawn by D. Broek may well discussed again that the relationship. Between the average inclusion distance T and the average microporous sized d is one to one. The crack model is put forward to explain the crack mechanism.