composition ratio of each alloy is adjusted according to its intended use in order to meet specifications. Aluminum alloys have the most expensive manufacturing cost for aircraft because their manufacturing process is energy-intensive. In order to obtain the aluminum to form the alloy, a smelting process must take place. Aluminum is extracted from bauxite, aluminum's main ore, through electrolysis, which requires a lot of energy; 211 MJ of energy are required to produce one kilogram of aluminum with electrolysis. Recycling aluminum is cheaper than manufacturing the alloy because it requires only remelting the used scrap. The remelting process is achieved at a lower temperature than electrolysis and therefore the process requires less energy, which lowers the cost. The recycled aluminum alloys can be used in aircraft parts such as stiffeners and flaps, where a growth in fatigue stress and fracture toughness are not critical to the component’s integrity. The alloys can also be used for non-aircraft applications, such as truck bodies, rivets, auto bumpers, and castings. Titanium alloys Titanium alloys are commonly used in the aircraft industry because they are strong and highly resistant to corrosion and heat. In comparison to aluminum, titanium is heavier but stronger, so less of it is required to form structural components, which reduces the overall weight and diminishes the in-flight energy consumption. Despite its natural abundance, titanium supply is limited when compared to other metals. The smelting process for titanium uses more energy than that of aluminum, consuming 361 MJ of energy for every kilogram of titanium produced. The recycling of titanium utilizes the scraps from the manufacturing process. These scraps are cleaned to remove oxygen and iron impurities and then remelted. Composite materials Composite materials are used to lower the weight of aircraft because they are lighter than traditional metal materials such as aluminum. They also have high fatigue strength (longer life cycle) and good corrosion and fire resistance. In order to decrease the weight of aircraft, manufacturers incorporate more composite materials to the structure. The lighter weight leads to improved fuel economy, which in turn reduces operational costs for airlines. A major component of composite materials is carbon fiber. If the carbon fiber is recycled, it does not lose its mechanical properties, which can be potentially used for the following applications: structural, acoustic and thermal insulation, and air and liquid filtration. Recycled carbon fibers are valued at up to $50 per pound