Abstract
Research on the lead-free solders has attracted wide attention, mostly as the result of the implementation of the Directive on the Restriction of the Use of Hazardous Substances in Electrical and Electronic Equipment. The Sn-Zn solder alloys have been considered to be one of the most attractive lead-free solders due to its ability to easily replace Sn-Pb eutectic alloy without increasing the soldering temperature. Furthermore, the mechanical properties are comparable or even superior to those of Sn-Pb solder. However, other problems still persist. The solution to overcoming these drawbacks is to add a small amount of alloying elements (Bi, Ag, Cr, Cu, and Sb) to the Sn-Zn alloys. Microstructure, tensile strength, and hardness of the selected Sn-Zn-Bi ternary alloys have been investigated in this study. The SEM-EDS was used for the identification of co-existing phases in the samples. The specimens? microstructures are composed of three phases: Sn-rich solid solution as the matrix, Bi-phase and Zn-rich phase. The Bi precipitates are formed around the Sn-dendrit grains as well as around the Zn-rich phase. The amount of Bi segregation increases with the increase of Bi content. The Sn-Zn-Bi alloys exhibit the high tensile strength and hardness, but the values of these mechanical properties decrease with the increase of Bi content, as well as the reduction of Zn content. The results presented in this paper may offer further knowledge of the effects various parameters have on the properties of lead-free Sn-Zn-Bi solders.
Highlights
Svi uzorci legura dobijeni su livenjem u grafitnoj kokili i hlađenjem na vazduhu, pa stoga imaju izraženu dendritnu strukturu
The results presented in this paper may offer further knowledge of the effects various parameters have on the properties of lead-free Sn–Zn–Bi solders
Summary
Poslednjih godina istraživači u mnogim zemljama rade na razvoju novih sistema bezolovnih lemnih legura. Novi sistem legura mora posedovati određene karakteristike u pogledu temperature topljenja, kvašljivosti, mehaničkih i električnih osobina [3]. Pored sistema Sn–Ag–Cu, koji se smatra sistemom koji najviše obećava kao zamena za Sn–Pb lemove, Sn–Zn sistem, čiji je ravnotežni dijagram stanja prikazan na slici 1, takođe se smatra kao prihvatljiva zamena za olovne lemne legure [5,6]. Energetsko disperzivni spektrometar (EDS) korišćen je za određivanje hemijskog sastava livenih lemnih legura i faza prisutnih u sistemu Sn-Zn-Bi. Merenje tvrdoće, pri opterećenju od 50 N, izvršeno je na uređaju za merenje tvrdoće po Vickers-u u tri tačke uzimajući srednju vrednost. Epruvete za merenje zatezne čvrstoće dobijene su pretapanjem legura u peći uz prisustvo pokrivnih topitelja, a onda su uzorci u obliku žice prečnika 1,9 mm dobijeni postupkom vakuum livenja. Izmerene su tri vrednosti za čvrstoću, pri čemu je uzeta njihova srednja vrednost
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