Effects of Al addition and heat treatment on microstructure and damping capacity of flake graphite cast iron

Abstract

Flake graphite cast iron has high damping capacity. Among the various theories on the damping mechanism of cast iron, the viscoelastic layer between matrix and graphite is an important factor. This indicates that the increase in surface area and quantity of graphite would be effective for improving the damping capacity of the cast iron. In this research, aluminum, which is a graphitizing element, was added to the flake graphite cast iron. The concentration of aluminum in the cast iron specimens was controlled from 0 to 7 mass%. The graphite and matrix structure were examined by optical microscopy and FE-EPMA, and the perimeter and area ratio of graphite in the cast irons and the damping capacity were measured. Addition of aluminum up to 5 mass% increased the area ratio and surface area of flake graphite in the cast irons. Addition of 3 ~ 5 mass% aluminum improved the damping capacity of the flake graphite cast irons, and that of 5 mass% aluminum cast iron was twice as compared with that of the cast iron without aluminum. This was attributed to the increase in the amount of graphite due to the addition of aluminum and to the refinement of the graphite, which contributed to the increase in the graphite surface area. Although the damping capacity of 7 mass% aluminum cast iron was smaller than that of 5 mass% aluminum one, it was higher than the cast iron specimens with the similar area ratio and surface area of flake graphite. This indicates that the κ phase observed in the as-cast high aluminum specimens and aluminum dissolved in the matrix of the heat-treated high aluminum cast iron specimens would have some effect for improving the damping capacity. The damping capacity at every temperature was decreased due to a heat-treatment in a condition, which decomposed the graphite.

Keywords

• cast iron
• aluminum
• microstructure
• flake graphite
• heat treatment
• damping capacity
• temperature