FRACTURE CHARACTERISTICS OF ALUMINUM CASTING ALLOYS

摘要

Al-Si casting alloys are widely used for engineering applications especially for automobile industry. Data on mechanical properties of such alloys, however, are not yet enough and many studies are now required. Fracture mechanisms in Al-Si system casting alloys are stated at first. Various morphologies of Si and a-dendrite in the alloys are examined in the relation to solidification microstructures and the presence of certain additives. Fracture behavior is analyzed in these alloys. Fracture toughness or impact toughness is measured and discussed. Effectiveness of modification of eutectic silicon morphology by Sr or Ca is specially stated. Furthermore, effect of impurity iron which is increased by recycling is also stated. Fatigue properties of Al-Si system alloys are presented. If there is no debris by coarse silicon on the specimen surface, K-N curve shows better fatigue strength rather than wrought 6061-T6 alloy. Increase of Si content leads to the increase of △K_th value, but the slope at the Paris region becomes large. Moreover impact fatigue test is conducted. Fatigue properties are generally degraded in this test. To assure the safety at impact collision during transportation of vehicles, exact dynamic stress-strain relationship is required for the simulation analysis. Dynamic tensile test using closed loop type high speed testing machine, therefore, is carried out up to the velocity of 12m/s.