Microstructure and Mechanical Properties of the Interface of Aluminum-Brass Bimetals Produced via Vertical Centrifugal Casting (VCC)

Abstract

Bimetal materials are composed of dissimilar metals, which are increasingly used to fabricate components that withstand harsh thermal and mechanical environments. In this work, aluminum-brass bimetallic hollow cylinders were produced using the vertical centrifugal casting process, and their interface was studied. Aluminum melt, with two different liquid-to-solid volume ratios of 1.5 and 2.5, was cast into brass hollow cylinders preheated to 100–400°C and rotated at 800, 1600, and 2000 rotation-per-minute. The sector-shaped samples were then studied using X-ray diffraction analysis, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. It was found that the interface consisted of three discernible layers. These included the chill zone (Al2Cu5Zn4 + Al3Cu3Zn) near the brass side, platelet precipitate zone (Al2Cu precipitates scattered in α-Al solid solution matrix), and finally anomalous (or divorced) eutectic grains (α-Al/Al3Cu) near the aluminum side. Mechanical tests were carried out, in particular Brinell, Vickers and compression tests. The findings revealed that the adhesion of the interface was reduced by increasing the thickness of the interface. Fractography of fractured surfaces illustrated the presence of flat faces (Al2Cu precipitates) locked together and deep depressions associated with cup-shaped dimples (α-Al/Al3Cu eutectic).