What materials make up most of the weight of an aircraft?
Besides aluminum alloys, most of an airplane's weight is steel, titanium, and composites. Here is a chart comparing the 747 and 777 structural weight, with a breakdown typical for similar airliners:


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Steel is used in components where strength or part life is most important, like landing gear and other important structural elements, as well as many fasteners. Titanium is used where weight and high temperature are important, such as around the engines. Composites are traditionally used for many less-structural applications such as panels and fairings, but may also be used in the empennage (tail surfaces) or on the interior as floor beams. Other materials will include alloys like nickel, as well as specialty materials like rubber, plastic, and fabric, which are used mostly in the cabin.

New aircraft like the 787 and A350 use composites much more extensively, replacing much of the aluminum. Titanium is also used more in these aircraft because it does not tend to corrode in contact with carbon fiber composite like aluminum does.


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Federico pointed out that the two graphics differ in the amount of aluminum on the 777 (70% on the first vs. 50% on the second), because the first chart shows only structural weight, while the second is overall.