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4130 CrMo is certainly more ductile than 6061 aluminum. 6061 is a precipitation- hardening alloy, it's excellent strength (for aluminum) comes at the expense of lower ductility and malleability. In other words, it's more brittle.

How exactly are you doing your "stiffness" calculations?

Using 6061 aluminum you should be able realize significant weight savings, provided you do your design work in a thorough and competent enough manner.

Designing the structure to be of equal weight in the aluminum may give you a significant safety factor in terms of strength. I say "May"........ "stiffness" is not really a function of yield strength, it is mainly a function of length, outside radius, and the elastic modulus (which is somewhat lower in Al) In other words, to increase stiffness in the aluminum you may wish to increase the outside radius of the tubing.

Also in terms of "denting" it's fair to compare a tube to a flat plate. Yield strength and toughness considerations aside, it's much more difficult to dent a flat plate when it is 2.5 times thicker.

Note that "safety factor" is something that is *designed into a structure,* it has nothing to do with the intrinsic properties of the material itself.....

Note that 4130 is equally subject to "work hardening." This is true of almost any ductile material, for example steel, aluminum, copper, nylon, etc.
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11 years ago. Rating: 1
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