Aluminum

By far the most common aluminum alloy in general use in this country is 6061-T6. Properties vary depending on who you ask but typical yield strength is around 30E6 to 35E6 psi with ultimate tensile strength about 15% higher than that. A Google search will turn up numbers. 6061-T6, along with all other aluminum alloys have approximately the same Young's modulus, about 10.0E7 psi. Good corrosion resistance, readily machined and welded, available in a bewildering variety of shapes and forms.

6061-T6 shapes are typically extruded, and they will have some internal stress that can lead to shape changes if lots of material is being removed. This is not normally a problem, but if you are designing a complex shape which you anticipate having machined out of a large piece of billet with lots of material removal, then you may want to consider a cast product. Mic-6 tooling plate, a proprietary alloy produced by Alcoa, is a good choice. The trade-off is lower strength, about a 25% reduction. Stiffness is unchanged. Any good machine shop will be able to obtain either alloy.