What Metal Is an Alternator Made Of?

The exterior housing of a modern alternator is constructed with cast aluminum. Aluminum has two advantages over steel in this application in spite of steel’s much higher strength. The first advantage is that aluminum is lighter by a factor of almost three. Every pound of mass that automakers can remove from a vehicle improves its fuel efficiency and handling, so the weight savings is very important. 

The second and more important advantage is that aluminum does not magnetize. An alternator is basically an electromagnet spinning at high speed to produce current, so a steel housing could potentially interfere with the operation of the alternator. 

Another exterior part of the alternator is the pulley, which is attached to the end of the rotor shaft and will typically be made out of steel.  

Inside your alternator you’ll find a steel shaft that holds the rotor, mounted on bearings at either end of the shaft. The rotor is made up mostly of wound copper, with a steel exterior. Just inside the aluminum housing of the alternator is the stator, which is also made up of wound copper. 

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