The frame material isn't really the issue -- most bikes can carry plenty of weight without a problem. The bigger issue is whether the bike is designed for touring, with attachment points for racks so you can distribute the weight of your gear. Wheels also could be an issue -- you want good, sturdy wheels rather than lightweight, low-spoke-count racing wheels for that kind of use.
I've toured all over the place on an aluminum bike with four large panniers, a back rack, and a bar bag. I don't know what kind of weight I carried, but I'm guessing with full camping gear and spares it was probably close to 70 lb. I weigh 175, and the only thing that ever broke in thousands of miles of touring was a spoke. If you're carrying a load, make sure you have well built and strong wheels.
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