The overhead transmission lines generally consists of Aluminium or Composite materials such as carbon and glass fiber.
Also we have International Standards for overhead lines :
The international standards covering most conductor types for overhead lines are IEC 61089 and EN 50182 and 50183.
||Round wire concentric lay overhead electrical stranded conductors
||Supersedes IEC 207 (AAC), 208 (AAAC), 209 (ACSR) and 210 (AACSR)|
||Conductor for overhead lines: round wire concentric lay stranded conductor
||Supersedes IEC 61089 for European use. BSEN 50182 identical|
||Conductor for overhead lines: aluminium–magnesium–silicon alloy wires
||Specification for general purpose galvanized steel wire strand
||For earth wire|
||Specification for copper and copper–cadmium conductors for overhead systems|
Even though copper based lines have a good corrosion resistance , Aluminium based lines are used since they are cost effective.