Abstract
Spreading tests for Cu substrate with Zn-Al eutectic-based alloys with 0.2, 0.5, and 1.0 wt.% of Na were studied using the sessile drop method in the presence of QJ201 flux. Spreading tests were performed for 1, 3, 8, 15, 30, and 60 min of contact, at the temperatures of 475, 500, 525, and 550 °C. After cleaning the flux residue from solidified samples, the spreading area of Zn-Al + Na on Cu was determined in accordance with ISO 9455-10:2013-03. Selected, solidified solder-substrate couples were cross-sectioned and subjected to scanning electron microscopy of the interfacial microstructure. The experiment was designed to demonstrate the effect of Na addition on the kinetics of formation and growth of CuZn, Cu5Zn8, and CuZn4 phases, which were identified using x-ray diffraction and energy-dispersive spectroscopy analysis. The addition of Na to eutectic Zn-Al caused the spreading area to decrease and the thickness of intermetallic compound layers at the interface to reduce. Samples after the spreading test at 500 °C for 1 min were subjected to aging for 1, 10, and 30 days at 120,170, and 250 °C. The greater thicknesses of IMC layers were obtained for a temperature of 250 °C. With increasing Na content in Zn-Al + Na alloys, the thickness reduced, which correlates to the highest value of activation energy for Zn-Al with 1% Na.
Highlights
The addition of Na to eutectic Zn-Al produces the NaZn13 precipitates that caused increased mechanical properties of cast alloys (Ref 1)
The characteristics of cast Zn-Al + Na alloys (Ref 1) undergoing the soldering process on a Cu substrate were determined in relation to time and temperature dependencies
The growth of intermetallic compounds (IMCs) during soldering on the Cu substrate was found to be controlled by volume diffusion for CuZn and CuZn4 phases, but by mixed volume diffusion and chemical reaction for the Cu5Zn8 phase
Summary
The addition of Na to eutectic Zn-Al produces the NaZn13 precipitates that caused increased mechanical properties of cast alloys (Ref 1). The Zn bonded with Na formed NaZn13 precipitates which could reduce the thickness of IMC layer at the interface. A similar effect was observed with the addition of Ag content to Zn-Al, which confirms the assumption that precipitates of AgZn3 are produced with Zn and reduce the thickness of IMC layer at the interface (Ref 2). The increasing wettability and IMC layer growth at the interface, caused by alloying elements (Ref 2-7), improved the mechanical properties of the joint. There have been few studies on the influence of time, temperature, and alloying elements in the soldering process on spreadability and the growth of the IMC layer at the interface. The Al4Cu9 phase formed at the interface inside the Cu5Zn8 layer which is in accordance with the phase diagram of the Al-Cu-Zn system (Ref 13)
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