A STUDY OF FATIGUE CRACK-GROWTH IN A PARTICULATE-REINFORCED AL-SI ALLOY AT 23-DEGREES-C AND 220-DEGREES-C

A study of short- and long-fatigue-crack growth in A356, a cast Al-Si alloy, reinforced with 20% volume fraction of silicon carbide (SiC) particulate, was carried out at 23-degrees-C. Long-crack growth tests were performed at 220-degrees-C. Short-crack growth was observed below the long-crack threshold stress intensity at 23-degrees-C and was dominated by interactions between the crack tips and the SiC particulate. In the long-crack tests at R = 0.1 and R = 0.5 a stress ratio effect on crack growth was observed at 23-degrees-C, which was more marked than that observed at 220-degrees-C. Examination of fatigue fracture surfaces revealed a matrix-dominated mode of crack growth at 220-degrees-C compared with that at 23-degrees-C where the SiC particulate played a significant role in the fatigue fracture process.