Thermal Properties of Intermetallic Phases at the Interface of Aluminum–Copper Compound Castings

Abstract

High-pressure die compound casting relies on high bond quality, and high thermal contact conductance at the interface is a key issue in the context of cast advanced cooling components, such as lightweight heat sinks for desktop and portable computers. The current study aims at enhancing the thermal contact between a copper insert piece and an AlSi9Cu3(Fe) cast alloy by developing suitable Zn-based coatings, which are used to establish a firm metallurgical bond between the solid insert and the cast alloy during highpressure die-casting. It is demonstrated by microstructural analyses that various phases form at the interfaces in the casting process. As the thermal conductivities of these phases have not been available, these are determined individually using a thermoflash device. The SEM investigations indicate that mainly ternary phases of the type Al x Cu y Zn z emerge in the bonding zone, as the high casting temperatures promote the diffusion of aluminum atoms into the coating. Interestingly, an alloy containing 50 wt% zinc reaches a thermal conductivity as high as 166 W mK À1 . The microstructural characteristic at the interfaces and the ramifications with respect to applications are discussed.

Increasing thermal conductivity in aluminium-copper compound castings: Modelling and experiments

“…Thus, the second parameter that needs to be controlled in order to design an efficient heat sink via compound casting is the thickness of the near eutectic layer. It appears that other approaches such as die casting [2], or centrifugal casting [28] would allow for reducing this critical parameter. In addition, a tailored melt treatment to reduce dissolved gases might be beneficial in combination with the current casting approach.…”

“…However, a key issue with compound casting is the presence of oxide layers that prevent wetting of the copper insert by the liquid aluminium. Wetting can be substantially improved by pre-coating the copper with a zinc-based layer [2], which acts as a bonding agent. With this approach, a firm metallurgical bond could be established and high thermal conductivity above 100 W/(m•K) was obtained.…”

Oxygen‐Free Production—From Vision to Application

“…Comparison of the data obtained by Fromm et al [ 62 ] (orange and blue) in comparison to literature results from ref. [79,80]. Reproduced with permission.…”

Vertical continuous compound casting of copper aluminum bilayer rods

“…The thermal conductivity of zinc-based intermetallic phases at the interface of an Al-Cu joint couple was investigated by Klose et al (2018). Due to the significantly lower thermal conductivity of intermetallic layers in contrast to most of the aluminum and copper alloys, the HTC was determined to be 50, 000 W m -2 K -1 at temperatures below the solidus point of the lower melting cast alloy.…”