Bronze, the first alloy, was probably discovered when copper and tin were accidentally melted together and allowed to harden. This alloy was found to be harder than either copper or tin. The materials in vehicles, especially in aircraft, must be strong for safety, and light for speed and economy. Alloys have been developed to meet these requirements.
Pure aluminium is light, but it is too weak for most construction purposes.
Several other metals can be mixed with aluminium to make a variety of alloys that are hard, durable, and light. One of the best of these alloys is duralumin. Duralumin is only slightly heavier than pure aluminium, and is about as strong as steel. Indium-bearing aluminium alloy combines low density with ability to achieve high strength through heat treatment alone. Tensile tests on peak-aged specimens indicated that alloy achieved yield strength approximately 15 per cent higher than baseline alloy.