Material Strength

Aluminum is stronger than forged iron, forged iron is stronger than cast.

Correct?

This answer can not be answered in a definitive "Yes" or "No". I'm assuming that even though you said Forged Iron, you mean Forged Steel. Iron is rarely used in anything automotive. Although it has a high strengths, it is extremely brittle and will crack/stress fracture easily. Forged almunium is generally not as strong as forged steel but is a lot lighter.

This website gives a nice summary on the different strengths and characteristics
http://www.63xc.com/scotn/metal.htm

This website gives specific numbers:
http://www.thedirtforum.com/materials.htm

More detailed information can be found by going to a library and researching "metallurgy" for about 30 min. I would def reccomend taking some time doing this if you plan on any modifications as most cars are, (you guessed it) based on metals and alloys.

Joe

actuall iron is used quite extensively in engine blocks.

Material--------------------Elastic Strength tens. (ksi)---- Ultimate Strength tens. (ksi)
Wrought iron----------------------30--------------------------48
Cast iron - malleable---------------32--------------------------50
Cast iron - nodular-----------------70--------------------------100
Aluminum Cast, 195-T6-------------24--------------------------36
Aluminum wrought, 2014-T4--------41--------------------------62
Aluminum wrought, 2024-T4--------48--------------------------68
Aluminum wrought, 6061-T6--------40--------------------------45
Steel SAE 4340--------------------132-------------------------150

Heres just a few out of my strength of materials book.