Abstract
The problems associated with the corrosion of aluminum connections, the low mechanical properties of Al/Cu connections, and the introduction of EU directives have forced the potential of new materials to be investigated. Alloys based on eutectic Zn-Al are proposed, because they have a higher melting temperature (381 °C), good corrosion resistance, and high mechanical strength. The Zn-Al-Si cast alloys were characterized using differential scanning calorimetry (DSC) measurements, which were performed to determine the melting temperatures of the alloys. Thermal linear expansion and electrical resistivity measurements were performed at temperature ranges of −50 to 250 °C and 25 to 300 °C, respectively. The addition of Si to eutectic Zn-Al alloys not only limits the growth of phases at the interface of liquid solder and Cu substrate but also raises the mechanical properties of the solder. Spreading test on Cu substrate using eutectic Zn-Al alloys with 0.5, 1.0, 3.0, and 5.0 wt.% of Si was studied using the sessile drop method in the presence of QJ201 flux. Spreading tests were performed with contact times of 1, 8, 15, 30, and 60 min, and at temperatures of 475, 500, 525, and 550 °C. After cleaning the flux residue from solidified samples, the spreadability of Zn-Al-Si on Cu was determined. Selected, solidified solder/substrate couples were cross-sectioned, and the interfacial microstructures were studied using scanning electron microscopy and energy dispersive x-ray spectroscopy. The growth of the intermetallic phase layer was studied at the solder/substrate interface, and the activation energy of growth of Cu5Zn8, CuZn4, and CuZn phases were determined.
Highlights
The Zn-Al eutectic system has been proposed as an alternative to soldering at high-temperatures, with a maximum working temperature is up to 350 °C (Ref 1)
Selected solder/substrate couples were cut perpendicular to the plane of the interface on a diamond wire saw, mounted in conductive resin, ground, polished, and subjected to microstructure and elemental analysis using FEI Quanta 3D FEG scanning electron microscope (SEM) coupled with energy dispersive x-ray spectrometry (EDS), in order to study the interfacial microstructure and the intermetallic compounds (IMCs) occurring at interface, the same as described in (Ref 2, 3)
The primary Zn phases were surrounded by eutectic phases, in which fine eutectic Si platelets were found to be dispersed in eutectic Zn matrix
Summary
The Zn-Al eutectic system has been proposed as an alternative to soldering at high-temperatures, with a maximum working temperature is up to 350 °C (Ref 1). This alloy has many desirable characteristics, including low cost, high mechanical properties, and good thermal and electrical conductivities. The effects of Si addition on the microstructure and mechanical properties of the Zn-Al alloy were examined. According to the results of this work, the effects of Si addition on the kinetics of formation and growth of the CuZn, Cu5Zn8, and CuZn4 phases in the spreading process were studied
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