Why does aluminum react exothermically with palladium?

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http://en.wikipedia.org/wiki/Pyrotechnic_initiator

Palladium-aluminium

Palladium-clad aluminium wires can be used as a fuse wire, known as Pyrofuze. The reaction is initiated by heat, typically supplied by electric current pulse. The reaction begins at 600 °C, the melting point of aluminium, and proceeds violently to temperature of 2200-2800 °C. The reaction does not need presence of oxygen, and the wire is consumed.

 

[chemisttree]

Now THAT's an example of a very exothermic alloying reaction!