Abstract
Compound casting is an attractive approach to create multi-material components and thus reduce the overall weight, while maintaining both the functional and mechanical properties. In this work, Al7SiMg alloy/copper compound castings were produced by a low-pressure die casting process. A flux coating was applied on copper pipes to reduce the oxide layer present in the interface between Al and Cu. The interface layer formed between the two alloys was investigated using optical microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Vickers micro-hardness was also measured across the interface. Results showed that a continuous metallurgical bond formed between copper and aluminum without use of surface treatment. In the bond layer, various Al–Cu intermetallic phases were detected, as well as primary silicon particles and the quaternary phase Al5Cu2Mg8Si6. Flux coating prevented formation of any metallic bond between copper and aluminum. Instead, high concentrations of potassium, magnesium and fluorine, indicative of formation of KMgF3 and MgF2, were detected in the interface. The mechanism for the formation of the intermetallic phases and the strength of the interface layer have been discussed.
Highlights
Recent development in the automotive industry has focused on lightweight components, which can reduce CO2 emission
This implies that aluminum melt has dissolved local areas of the copper pipe surface, which differs from the interfaces observed in castings A and B where large continuous reaction layers were observed
Tavassoli et al suggested that more copper-rich phases form between Al2Cu and Cu through solid-state phase transformation once the temperature drops below the eutectic temperature.[27]
Summary
Recent development in the automotive industry has focused on lightweight components, which can reduce CO2 emission. Aluminum–copper bimetallic components can be used in wires and bus bars where conductivity is an important factor.[1] Compared to Al–Cu alloys, Al–Cu bimetallic components can reduce both weight and cost without reducing electrical and thermal conductivity.[2] A challenge is, that aluminum and copper have high affinity to each other, especially at elevated temperatures. This causes formation of brittle intermetallic phases with high electric resistance.[3] More importantly, both metals are subjected to oxide formation on the surface. Oxides are known to reduce wettability and will prevent formation of a metallurgical bond between aluminum and copper.[6]
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