Influence of Age Hardening on Mechanical Properties of Cast Nickel-Aluminum Bronze Containing Shrinkage Porosity

Abstract

In this study, the effect of porosity on hardness and strength of as-cast and aged nickel-aluminum bronze (alloy C95800) has been investigated. Optical and scanning electron microscopes were used to examine the microstructures and to characterize the fracture surfaces of the alloy, respectively. After aging, α grains in the microstructure were refined, distribution of eutectoid particle phases became more uniform and volume fraction of β’ phase was increased. Hardness testing revealed that optimum aging was achieved at 350 °C with more than 90% increase compared to the as-cast alloy. In order to eliminate the effect of pores on tensile data, and to evaluate aging process in terms of tensile strength, the concept of “effective area” was introduced as the total cross-sectional area minus the projected area of pores as obtained by fractography. Based on this concept, the effective strength of the cast alloy was calculated. The effective strength was also obtained by Ghosh’s model; comparison of the results indicated good agreement of both methods. It was concluded that effective strength presented in this research could be an appropriate reference value when considering mechanical properties of porous casting alloys.