Tellurium improves the machinability of copper.
Tellurium is usually added to copper to improve machinability ("free cutting").
ASTM specification B301 has 0.5% tellurium; at concentrations of up to 0.75% machinability is improved while electrical conductivity and hot working behavior is maintained.
Mechanical properties are similar to tough pitch copper, while machinability is similar to brass - the hardness of the alloy is increased by precipitation of the copper telluride: weissite.
[2] Tellurium copper can be used as the electrode in electrical discharge machining (EDM) - the alloy is used to replace copper when grinding wheel loading occurs during fine finishing of the electrode - the alloy retains the properties of copper in the EDM process.