Aluminum alloy bats have grown in popularity over the past few decades. While Major League Baseball only allows the use of wooden bats, almost every high school and college in the nation has made the switch to aluminum alloys. The reasons behind these switches are both economic and performance based. The aluminum bats may cost more individually than wooden bats, but they break less often and therefore save money in the long run. The material properties of aluminum alloy bats also give a clear advantage to a hitter by allowing him to hit the ball farther and more consistently. The following sections cover the properties of aluminum alloys in bats, the specific alloys that are used, and the processing methods used in creating aluminum bats.
There are many properties of aluminum bats, which make them favorable to their wooden counterparts. These properties stem from the microstructure of aluminum alloys. Aluminum alloys usually exist in hexagonal close packed or face centered cubic crystal structures. The positive metal ions exist in a closely packed network floating in a "sea of negative electrons." The ability of the electrons to flow from one place to another within the metal is what gives them favorable qualities such as conductivity, malleability, and strength. When different elements are mixed together in the crystal structure we create alloys. Atoms of nearly equal size will from substitution alloys, while smaller atoms can sneak in between the larger ones to form interstitial alloys. By mixing various amounts of different atoms together, it is possible to alter the bonding and change the properties of the metal. Bat manufacturers have done this to create alloys with properties beneficial to hitting a baseball. .
The physics of hitting a baseball involve transferring the momentum of the bat to the ball. Momentum is defined as mass times velocity so it is immediately obvious that the weight of the bat and the speed with which you swing will play a key role in how far the ball can be hit.