TricycleTom

The really cheap bikes are still all steel, right down to their slippery-when-wet rims. but Robert Persig's comment on steel applies to all alloys. People who don't work with metal tend to think that it exists in immutable shapes. A metalworker tends to think of it in terms of basic physical properties. You can get it to be any shape you want if you are skilled enough, and any other shape if you are not. There isn't even any steel in nature - anybody from the Bronze Age could have told you that. "Aluminum" runs the range from pure, soft metal to strong, brittle alloys. It overlaps a lot with cheap stainless steel in strength, but never in stiffness. The low density of aluminum allows it to be used in larger tubes, gaining strength and stiffness, but losing on wind resistance.
There are people who ask for carbon fiber to be fashionable, and I tend to give up trying to help them, and let someone else overcharge on the deal.