WORK SOFTENING OF ALUMINUM BASE ALLOYS CONTAINING NANOSCALE ICOSAHEDRAL PHASE

Melt-spun Al93Mn5Ce2, Al92Mn6Ce2 and Al94.5Cr3Ce1Co1.5 ribbons consist of nanoscale icosahedral (I) particles surrounded by fcc-Al phase wit hout grain boundaries. The ribbons were cold rolled to 70% reduction i n thickness (R-c) and the rolling causes significant decreases in hard ness and tensile strength. The particle size and interparticle spacing of the I-phase decrease by rolling, accompanying the increase in the area of the I/Al interface. However, no dislocation was observed in th e cold-rolled Al and I phases. The absence of dislocations is because the interface acts as a sink of dislocations, leading to the work-soft ening. The softening phenomenon reflects an inverse Hall-Fetch relatio n in which the yield strength and hardness decrease with decreasing gr ain size in the size region below about 30 nm because the interparticl e spacing of the I-phase decreases from 15-25 nm to 5-10 nm by cold ro lling to 30 to 70% reduction in thickness. This phenomenon is importan t for better understanding of deformation and strengthening mechanisms of the nanostructure alloys.