무연청동의 조직과 주조성에 미치는 Bi 및 Sb 첨가의 영향

Abstract

The effects of Bi and Sb additions on the microstructures and casting properties in lead-free Cu-Zn-Sn bronze were investigated. (1) When only Bi was added to the bronze, Bi was precipitated on the δ phase of α dendrite cell boundary. When Bi and Sb were added together, Bi was precipitated on the δA which was the Sb-rich area in the δ phase. (2) The addition of Sb accelerated the formation of δ phase, and when Sb, Bi and Pb were added, Bi and Pb were precipitated as mixed solution in the δA phase. (3) The combined addition of Sb and Bi resulted in the suppression of shrinkage due to the complementary effects of the mass feeding of α-dendrite cluster covered with δ phase and sealing of micro-shrinkage in the δ phase by solidification expansion of Bi. (4) Only Bi was added to the bronze, vickers hardness was decreased. On the contrary, only Sb addition resulted in the increase of the hardness. When the Bi and Sb were added together, vickers hardness were also increased.