Effect of Cu Addition to Zn-12Al Alloy on Thermal Properties and Wettability on Cu and Al Substrates
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ODUCTION
THE development of modern technology and the production of more advanced electronic devices has caused an increase in the demand for new construction materials and thus stimulated the development of new materials combining single and multiple elements. Lead-free soldering was, and still is, a great challenge for many industries, and it requires not only the development of new solder, but also of fluxes, and potentially even changes in the manufacturing processes. The electrical and electronics industries have developed replacements using the addition of alloying elements to lead-free and tin-based soft solder that melts at 503 K (230 C).[1–5] However, the automotive and cooling industries have used solders with higher melting points.[6] Therefore, an important task is to develop new solders with appropriate wetting properties, melting points, mechanical strength, etc. In response to market demand from the aerospace, automotive, and electronics industries, solder alloys for use at temperatures up to 623 K (350 C) have been developed, on the basis of eutectic ZnAl alloys with added Ag,[6] In,[7] and Cu.[8,9] The major contribution of the Vianco team,[10] which worked on alloys in the temperature range above 573 K (300 C), is noteworthy. Yet their new ecological alloys still did not yield very TOMASZ GANCARZ and JANUSZ PSTRUS´, Assistant Professors, are with the Institute of Metallurgy and Materials Science, Polish Academy of Science, Krakow, Poland. Contact e-mail: t.gancarz@ imim.pl SYLWIA MOSIN´SKA, PhD Student, is with the Wroclaw University of Technology, Wroclaw, Poland. SYLWIA PAWLAK, Assistant Professor, is with the Wroclaw Research Centre EIT+, Wroclaw, Poland. Manuscript submitted March 24, 2015. Article published online November 5, 2015 368—VOLUME 47A, JANUARY 2016
good results, so further research has been conducted by Takaku,[11] Kang,[12] and Savaskan,[13] to improve the alloy properties. The proposed eutectic ZnAl alloys have a higher melting point, of 654 K (381 C), after the addition of Cu, and they demonstrate good corrosion resistance and high mechanical strength.[8–10] The intermetallic phases (IMPs) in the Cu-Zn system have a very important role in the joining of metals.[11–14] Therefore, the formation of IMP layers on a Cu substrate has a significant impact on the properties of the joints. The aim of this study was to characterize Zn-Al-Cu alloys in terms of melting temperature, coefficient of linear expansion, electrical resistivity, tensile strength, contact angles, and spreading area on Cu and Al substrates, and to determine the effect of Cu in a ZnAl alloy on the formation of IMPs, during the soldering process on Cu substrates.
II.
EXPERIMENTAL
The alloys were prepared using pure (99.999 pct) Zn, Al, and Cu in an argon-filled glove box, with oxygen and with a moisture level below 1 ppm. The studied alloys were based on eutectic ZnAl with the addition of 0.5, 1.0, and 1.5 at. pct Cu; their final compositions are shown in Table I. Transition temperatures for the solder alloys were dete
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