I found this, thought it was interesting..............................
Aluminum
Aluminum is lighter in weight which increases control and bat speed. Balls travel farther with aluminum over other metals. Despite generally higher costs than other materials, aluminum is durable and not prone to crack or break Aluminum bats come in a variety of alloys each with a different weight
Generally, lighter aluminum alloys are thinner and more durable. The one thing these have in common is that they are all different combinations of Zinc, Copper, Magnesium and Aluminum. Most modern bats are made of aircraft-grade aluminum supplied by Alcoa or Kaiser. Variations in the alloy formula have resulted in stronger alloys, allowing the manufacturers to design bats with thinner shell walls, which in turn corresponds to lighter weight. All of these advanced alloys are known by trade names (usually a number), as well as brand names (sometimes the same grade will be marketed under a different brand name by different bat makers). The brand names are heavily hyped: you can be sure that if a bat is made of an advanced alloy, that fact will be trumpeted somewhere on the bat, usually in large bold letters. By the same token, you should beware of bats -11 or lighter that do not state the type of alloy used. They will probably be made of an alloy that is too weak to support the thinner wall required for the light weight. The following is a list of the different alloys and their benefits. 7046: This is the standard aluminum alloy used in most bats. Standard aircraft aluminum is designated in the trade as "7046". Most budget bats are made of this grade. CU31/7050: More durable than 7046, due to increased levels of zirconium, magnesium, and copper; is about 33% stronger than 7046. About 12 years ago, Alcoa branded its 7050 grade "CU31" and began marketing it in Slo-Pitch bats as the first high performance alloy. The "CU" designation refers to the addition of copper to the alloy.
C405/7055: Increased Zirconium content than 7050, giving higher strength. Alcoa's "C405" is the next higher grade, supposedly about 10% stronger than CU31. C405 as introduced 8 or 9 years ago, quickly followed by C405 Plus and C405 Ultra, which are the same alloy manufactured under difference processes. The strength difference between C405 and C405 Ultra is only about 5%. C405 Ultra is, therefore, about 38% stronger than standard aircraft aluminum.
C555: 7% stronger than C405, has traces of scandium, which increases strength. "7075" is a new alloy by Kaiser that is claimed to be equal to or better than C405 Ultra. Kaiser's Sc500 Scandium, and Alcoa's C500 and C555 represent the next level up. C500 and Sc500 Scandium are about 3-5% stronger than C405 Ultra, respectively. C555 is claimed to be about 7% stronger than C405 Ultra, or about 40% stronger than standard aircraft grade aluminum.
The current king of the hill is SC777, made by Kaiser. While the other exotic alloys only offer incremental strength gains over CU31, SC777, if the claims are true, represents a truly big leap: about 50% stronger than C405. This means that SC777 is nearly twice as strong as standard aircraft aluminum.
Aluminum bats, and those enhanced with other alloys, also come in single-layer or double-layer construction
Double-layer bats offer more durability and power, since the ball rebounds off the bat with more authority
Cryogenically treated aluminum--Alloy is frozen and reheated to provide greater durability, less vibration and 2-4% greater distance
WHY ALLOY GRADES MATTER (AND WHY THEY MAY NOT) There's a lot of hype out there about the various alloys. Here's why alloy grade really matters. Manufacturers use advanced alloys in order to be able to make the walls of the barrel of the bat thin while still allowing the bat to be strong enough to resist denting. Thin walls equal light weight. Thin walls are also claimed to contribute to a "trampoline" effect, or rebound, when the bat strikes the ball. The rebound effect enhances power, and therefore, distance, given the same swing speed. Think of throwing a baseball against a wall made of superball material, then against a wall made of concrete. Other than allowing for thinner walls, however, there is little power to be gained from the exotic alloys themselves. The various alloys have virtually the same specific gravity, so the walls of a -11 CU31 bat are likely to be the same thickness as those of a -11 SC777 bat. There may be some difference in the trampoline effect, but it is negligible. A good rule of thumb: stick to baseball bats made of CU31 or 7050 alloy or better for -10 bats, at least C405 for -11 bats, and C500 or better for -12 bats. If your child is 11 or 12 and uncommonly large and strong, consider Sc777. If the bat is -9 or heavier alloy grade is not that important.