So-called stress cracks are really fatigue cracks, due to repeated cycles of high stress followed by low stress. Steel and titanium have what is called an endurance limit; if the stress is below the endurance limit, you can cycle a steel or titanium component an unlimited number of times without fatigue cracks starting or growing. That is why steel crankshafts, connecting rods, valve springs, transmission gears, axles and suspension springs are usually made of steel (or titanium in your Porsche race car).

Aluminum does not have an endurance limit - if you put enough stress cycles into it, it will crack, even at a low stress. While you are worrying about your horse trailers, worry more about the airplanes over your head. The airplanes all have aluminum wing spars, and the spars all have cracks. It is just that Boeing and the airlines (except for maybe Alaska and America West and others that Inspector knows about) know where the cracks are, how fast they are growing, and how many more flight cycles before the wings are replaced.

Properly designed and tested aluminum framed trailers can last a long time, but when they do eventually crack (might take 40 years) their time is up. For example, aluminum has been used successfully in boat trailers for many years. But I would agree, don't buy a pre-cracked trailer ! ! !

Most of the big-rig box trailers you see behind the Freightliners and the Navistars and the Peterbilts and the K-whoppers are built with steel frames and aluminum bodies, but as Tanker says they have carefully applied insulating plastic layers and zinc chromate primers to prevent the galvanic corrosion of the dissimilar metals. Is the average horse trailer built with the same technology and quality control?

Hope this helps you in answering your dilemma,

Dr. Lee