RADIAL MICROSTRUCTURAL HETEROGENEITY, CHEMICAL COMPOSITION, AND HARDNESS OF A CENTRIFUGALLY CAST CU–AL–ZN–FE ALLOY BUSHING

Abstract

The radial microstructural and mechanical heterogeneity of a centrifugally cast multicomponent copper-alloy bushing intended for a travel wheel was investigated. The analysis combined macrostructural examination, chemical analysis performed in quadruplicate, optical metallography at magnifications ranging from 50× to 800×, and Brinell and Rockwell B hardness measurements. A dendritic region was identified adjacent to the outer surface, whereas a region of equiaxed grains was observed toward the inner surface; no visible macroscopic defects were detected. The average chemical composition was 77.0 wt.% Cu, 8.50 wt.% Zn, 6.45 wt.% Al, 4.63 wt.% Fe, 1.00 wt.% Ni, and 0.871 wt.% Pb, with the complete set of measured elemental concentrations totaling 99.95 wt.%. The microstructure was interpreted as comprising an α-Cu matrix, β′-like regions, and Pb-rich inclusions, whose prevalence increased toward the middle and inner portions of the wall. The mean hardness values were 115 ± 2.65 HBW 5/250 and 58.5 ± 0.78 HRB. The results demonstrate good repeatability of the chemical-composition and hardness measurements, together with radial microstructural heterogeneity consistent with directional solidification and centrifugal segregation. Because the radial location of the specimen used for chemical analysis was not documented, the measured composition cannot be extrapolated to the entire bushing. The phase constitution and fitness for service should be further verified by X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), radial compositional mapping, and mechanical and tribological testing.