Abnormal structure and properties of copper–silver bar billet by cold casting

Abstract

Copper alloy rod billet with 20% silver was prepared using homemade three-chamber vacuum cold-type vertical continuous casting equipment. The variation rules of the microhardness, eutectic ratio, and size and distribution of silver particles precipitated in the primary α-Cu phase at the end of the continuous casting alloy rod blanks were studied using a microhardness tester and scanning electron microscope. The obtained results show that when the cold-type vertical continuous casting speed is 120 mm·min−1, there is obvious reverse segregation of solute element near the end of the prepared ∅7.8 mm copper–silver alloy rod blank. From the end of the continuous casting alloy rod blank to 5 mm from the end, the Cu–Ag eutectic structure in the copper–silver alloy increases from 13.4 to 15.9%, and the size of Ag particles precipitated in the primary α-Cu phase increases from 100 to 350 nm. The microhardness increases from 56 HV0.05 to 85 HV0.05. When the distance from the end exceeds 5 mm, the microstructure and properties of the continuous casting alloy rod blank are basically stable.

Keywords

• cold-type vertical continuous casting
• copper–silver alloy
• microhardness
• microstructure at the end of bar billet
• inverse segregation