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Reading Selection, Lesson 18

About Alloys

Alloys are mixtures that contain at least one metal. Most alloys are solid   solutions. Although many alloys consist of two metals mixed together (for example, silver and tin in some solders), the most widely used alloy is the mixture of carbon and iron that is called steel. Steel is much stronger than pure iron. Its properties can be changed by adding other substances to it. For example, manganese makes steel harder, and chromium, which is used to make stainless steel, stops steel from rusting.

Alloys of other metals, such as aluminum and titanium, provide the high-strength, low-density materials needed to make aircraft. Alloys of tungsten and cobalt are used in materials that must resist the effects of high temperature (for example, rocket engines). Bronze is an alloy of copper and tin. Pure gold is very soft, causing items made from it, such as jewelry, to be easily damaged. Therefore, gold is often alloyed with silver and copper to produce a harder metal. You will learn more about some of these metals in Lessons 21 and 22.


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