Using Recycled Bismuth-Tin Solder in Novel Machinable Lead-Free Brass

Abstract

The aim of this work was to create and apply a recycled bismuth-tin (Bi-Sn) solder in novel machinable lead-free brass. The Bi-Sn alloys were obtained from a recycled solder used in the electronics industry to reduce cost and to partially solve electronic waste issue. The relationship between mechanical properties, microstructures and machinability of the brass were investigated. The results showed that a based lead-free Cu-38Zn-0.5Si brass without Bi-Sn alloy addition exhibited highest tensile strength, required the highest machining force and produced an undesirable long continuous chip type. An addition of 1-3 mass% Bi-Sn alloy resulted in signi cant decrease of both the tensile strength and the machining force. The chip formation changed from an undesirable long continuous chip to a discontinuous chip in moderate size. On the other hand, the addition of 4 and 5 mass% Bi-Sn alloy slightly increased the tensile strength and the machining force, the chip formation changed from a moderate chip size to a very short chip under every test condition. The lead-free brass with 3 mass% Bi-Sn alloy showed the best effective machinability as it required the lowest machining force and produced a short chip. Furthermore, the mechanical properties were about the same as those of the commercial EnviroBrass ® III. Thus, the recycled Bi-Sn alloy can be used to improve the machining properties of lead-free brass and offers a possibility for new and better lead-free brass alloys.

Bismuth Formation in Lead-Free Cu–Zn–Si Yellow Brass with Various Bismuth–Tin Alloy Additions

“…The phase transformation of these alloys related with zinc equivalent were explained in details in our previous work. 21) In addition, Fig. 1(a) of specimens with 1 mass% BiSn alloy additions showed that the bismuth particles were embedded in the beta phase and at the alpha-beta phase boundaries.…”

“…Lead-free brass in this study consisted of Cu38Zn with 0.5 mass% silicon with various 14 mass% BiSn alloys, as described in details in our previous work. 21) The alloys were prepared with high purity copper (Bangkok Assays, ²99.5%), zinc (Padaeng Industry, 99.9%), silicon (S.M. Chemical Supplies, 99.5%), and a recycled electronic solder, which is an alloy composed of 52Bi48Sn.…”

“…Since the total zinc equivalent of the studied composition was in the range of 4144 as reported in our previous work. 21) In the case of 44% zinc equivalent as shown in Fig. 4, when the temperature of the liquid alloy was cooled to 908°C at the liquidus line (at point A), the freezing began where the ¢ phase crystallized.…”

“…1219) Recently, bismuth has been added to certain copper alloys to enhance the machinability. 20,21) Bismuth has similar properties to lead including low melting point and no solubility in copper. However, bismuth in copper alloys segregated in form of thin films along the grain boundaries.…”

Machinability of Eco-Friendly Lead-Free Brass Alloys: Cutting-Force and Surface-Roughness Optimization

“…A lead-free machinable brass (CuZn40) exhibiting good balance between the elongation and the machinability was obtained by using the mixed powder containing 0.5 wt % graphite particles and 2.2 wt % Bi additions [11]. Relevant research revealed the benefits of the recycled bismuth-tin solder addition in lead-free brass alloy (Cu-38Zn-0.5Si) by reducing the chip-size morphology as well as the required cutting force [12]. The improvement of chip-breaking efficiency was attributed to the presence of κ-phase in CuZn21Si3P, as opposed to the effect of α-phase in CuZn38As brass.…”