Phosphor Bronze

Overview

Phosphor Bronzes, or tin bronzes, are alloys containing copper, tin and phosphorous. The phosphor bronzes contain between 0.5 and 11% tin and 0.01 to 0.35 % phosphorous. The addition of tin increases the corrosion resistance and strength of the alloy. The phosphorous increases the wear resistance and stiffness of the alloy. The phosphor bronzes have superb spring qualities, high fatigue resistance, excellent formability and solderability, and high corrosion resistance. They are primarily used for electrical products, other uses include corrosion resistant bellows, diaphragms, and spring washers. The phosphor bronzes are designated as UNS C50100 through C54200. Leaded phosphor bronzes combine good strength and fatigue resistance with good machinability, high wear resistance and corrosion resistance. They are used in applications such as sleeve bearings, thrust washers, and cam followers. They are designated as UNS C53400 through C54400.

The microstructure of wrought phosphor bronzes contain the twinned grains typical of copper alloys. The tin remains in the alpha copper solid solution. The phosphorus forms a copper phosphide phase. The phosphor bronzes have a wide freezing range and extensive segregation of the alloying occurs on cooling. The material that cools first are dendrites of the copper rich alpha phase. The dendrites are heavily cored, or contain a range of compositions over their thickness. The second phase to form is tin rich, initially transforming to beta, and finally to a mix of alpha and delta. The alpha and delta phases form in between the dendrites. The phosphor rich phase solidifies last as the eutectic composition of copper phosphide. The dendrites are broken up during working and annealing, the resulting structure consists of grains of alpha copper and are of the alpha and tin rich delta phases, and copper phosphide.

NOTE: The file size of the Larger and Largest View of the Micrographs are substantially larger than the thumbnail shown. The Larger View images range in size from 11K to 120K depending on the image. The Largest View images range in size from 125K to almost 500K.