Hard Silver Ag[97-98%], Cu+Ni
General application relays. The copper and nickel contents give hardness. Long contact life, but tends to oxidise at higher temperatures.
Silver Nickel AgNi
A good standard contact material. More resistant to welding at high loads than hard silver. High burnout resistance.
Silver Cadmium Oxide AgCdO
More resistant to welding at high switching current "peaks" so is used for high AC loads because. Not recommended for strong DC breaking arcs because of the wear this creates.
Silver Tin Oxide AgSnO2
Material is more resistant to welding at high making current peaks due to the tin oxide. Has a very high burn out resistance when switching high loads. Low degree of material migration under DC loads. Useful where very high inrush currents occur. Silver Tin Oxide is frequently chosen as the replacement relay contact material for Silver Cadmium Oxide which is more harmful.
Silver Tin Indium AgSnOinO
Similar to Silver Tin Oxide but more resistant to inrush.
More resistant to welding at high loads than hard silver, with high burnout resistance.
Gold Plating 10µm Au
Used for switching low loads > 1mA/100mV. The plating will be removed by friction and erosion after around 1 million switching cycles in "dry circuits".
Gold Plating / Flash 3µm Au
Same qualities as 10µm Au but is less durable. It is generally used to prevent corrosion / oxidation of relay contacts during storage.