The grain-boundary segration of Fe, Co and Ni in pure aluminum and its effects on mechanical properties

Abstract

The solid solubility limit of Fe, Ni, or Co in aluminum is extremely low, but these elements have very fatal effects on the physical and chemical effects of aluminum.The grain-boundary segregation in aluminum specimens containing 0.006-0.04 at % of Fe, Ni, or Co was studied by using low-frequency internal friction and Instron tension tester.The specimens were water-quenched after being preheated at 620 or 630°C, and then, the grain-boundary relaxation and work hardening at 90°K were measured.The results obtained were as follows.1. Fe, Ni, or Co greatly lowered the grain-boundary peak and high-temperature background of internal friction. The above facts expressed that these elements were segregated near grain-boundaries to inhibit boundary sliding or migration.2. Fe, Ni, or Co greatly improved the work hardeness of 90°K. The maximum value of hardness index was observed at about 0.013 at % of Co in Al-Co system or at about 0.032% at % of Fe in Al-Fe system. The above behavior was explained by either the increase in the back stress for the propagation of dislocation or the rapid multiplication of dislocation near the segregated grain-boundary.It is concluded that most of Fe, Ni, or Co atoms in aluminum are segregated near grain-boundaries or sub-boundaries even at as low as 620°C. The boundary segregation is more remarkable when the temperature is lower.Substitutional solid solubility limits of these elements in aluminum lattice will be much lower than the values reported in the past.