Lets see... *opens "Materials and Processes in Manufacturing" textbook*...
First, ALuminum:
"A number of unique and attracitve properties account for the engineering significance of aluminum. these incluce its workabilty, lightweight, corrosion resistance, good electrical and theramal conductivity, optical reflectivity, and ease of recycling. Aluminum has a specific gravity of 2.7 compared to 7.85 for steel, making aluminum about one third the weight of steel for an equivanlet volume. Sost Comaprisons are often made on the basis of cost per poun, where aluminum is at a distinct disadvantage. There are a number of applications, however, where a more appropriate comparison would be based on a cost per unit volume. A pound of aluminum produces three times as many same sized parts as a pound of steel, so the cost difference becomes markedly less. "
Now, Steel:
"Compared to other engineering materials, the carbon steels offer high strength and high stiffness, coupled wit reasonable toughness. They can be magnetically seperated from mixed materials, and are easily recycled. Unfortunatly, they also rust easily and generally require some form of surface protection, such as paint, galvanizing, or other coating. The plain-carbon steels are genearlly the lower-cost steel material and should be given first consideration for many applications. Their limitations, however, may become restrictive. When improved performance is required, these steels can often be upgraded by the addition of one ore more alloying elements......Steel is an extremely useful engineering material. It offers strength, ridigity, and durability. From a manufacturing perspective, its formability, joinability, and paintability, as well as repairability, are all attractive. As a result, steel accounted for half of the material used in a typical 2000 model Japanese passenger car, and will likely continue at this level. In terms of tonnage, steel is the most recycled material in commerce, nearly twice as much as paper, and far exceeding aluminum, glass, and plastics. Its magnetic properties facilitate easy recovery and seperation from other materials. As a result, about two thirds of the steel production in the United States comes from the recycling of steel scrap."
well there you have it....I knew tackling a course like design and processes of metallurgy and material sciences in college would lead to something.
In my many years in FIRST, I have always had a sweet spot in my heart for aluminum. I think the engineering and properties that it has makes it beautiful. For any of those who cannot come to a decision over steel vs. alum. Look into aqcuiring this book( however be forwarned, it does cost about $150).
Hope everything works out!, Good luck!