In the previous paper, it was reported that the forged and extruded P/M aluminum alloys with ultra-fine grain (200-500 nm) have relatively lower ductility and fracture toughness, and that fatigue crack growth resistance was lower than that of the conventional P/M Al alloys. In this study, the extruded material was upset forged at various forging ratios in order to improve the ductility. Fatigue crack growth tests were carried out using L-C and C-C orientation CT specimens of the extruded and

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... et forged materials, and the effect of pre-plastic working on fatigue crack growth behavior was investigated. Fracture toughness was improved by the upset forging, irrespective of specimen orientation. Fatigue crack growth resistance of the pre-plastic worked alloys became higher than that of the extruded one in the L-C orientation specimens. However, crack growth threshold value in the C-C orientation specimens, ΔKth, became low for upset forging and remarkable anisotropy of fatigue crack growth resistance was observed.