Alumel is used with chromel in thermocouples. Oxidation is related to the reactivity series of metals, as aluminium and chromium are relatively near the top of the reactivity series they can be oxidised relatively easily. Nickel, on the other hand is near the bottom and is pretty unreactive, this may be why alloys are used to prevent oxidation.
Copper is below nickel in the reactivity series.
If either chromel or alumel were used in an electrochemical cell against copper ions the metals of the alloys would be lost to produce solid copper as copper is lower in the reactivity series than chromel and alumel.