Interface Formation and Characterization of Brass/Aluminum Compounds Fabricated Through Die Casting and Semi-Continuous Casting

An innovative method based on the static and semi-continuous casting technology is investigated for the production of bilayer brass/aluminum billets and rods. The paper focuses on the interface formation and characterization of metallurgically bonded hybrids consisting of brass CuZn37 and the aluminum alloys AA5083, AA6060 and AA7075. Depending on the thermal process conditions, the interfacial reaction zone between the joining partners exhibits a thickness between a few micrometers and a few millimeters. Regardless of the usage of disparate aluminum alloys, the interface of as-cast brass/aluminum compounds is characterized by four intermetallic layers, namely CuZn (CuZn-beta) as well as an anomalous eutectic area of aluminum solid solution (alpha-Al) and eutectic structures. The intermetallic layers are primarily formed by solid-state diffusion, whereas the anomalous eutectic zone is a result of dissolution of Cu in liquid Al and subsequent solidification and precipitation. The microhardness, elastomechanical properties and the bonding strength of the interfacial area of as-cast compounds are determined using the nanoindentation and push-out testing technique. Due to the high cooling rates, brass/aluminum compounds fabricated through semi-continuous casting are characterized by a sufficient geometrical stability of the interface and high bonding quality.