Metal Alloys Explained
Properties, Composition, and Production of Select Metal Alloys
Alloys are metallic compounds made up of one metal and one or more metal or non-metal elements.
Examples of common alloys:
- Steel: A combination of iron (metal) and carbon (non-metal)
- Bronze: A combination of copper (metal) and tin (metal)
- Brass: A mixture of copper (metal) and zinc (metal)
Properties
Electric conductivity, high strength and durability, heat and corrosion resistance, or other useful properties may be available for each individual pure metal. Commercial metal alloys try to combine these beneficial properties to produce metals more useful than any element of their application.
For example, steel needs the correct combination of carbohydrates and iron (approximately 99% iron and 1% carbon), to create a metal that is stronger, lighter and more workable than pure iron.
It is hard to calculate precise properties of new alloys because elements not only become a sum of the components. They are formed by chemical interactions that depend on component parts and specific processes. In the development of new metal alloys a lot of tests are therefore needed.
Melting temperature is a key factor in alloying metals. Galinstan®, a low-melt alloy containing gallium, tin, and indium, is liquid at temperatures above 2.2°F (-19°C), meaning its melting point is 122°F (50°C) lower than pure gallium and more than 212°F (100°C) below indium and tin.
Galinstan® and Wood's Metal are examples of eutectic alloys—alloys having the lowest melting point of any alloy combination containing the same elements.
Composition
Thousands of alloy compositions are created on a regular basis and new compositions are formed annually.
The accepted standard compositions contain the pure elements (based on the weight content) of constituents. The make-up and mechanical and physical properties of specific alloys were regulated by international organisations, such as ISO, SAE International and ASTM International.
Production
Certain metal alloys happen naturally and require little processing for industrial grade materials. For instance, ferro-alloys such as ferro-chrome and ferro-silicium are made by mixed ores smelting and used in the production of different steels. But you would be wrong to believe that metal alloy is a simple process. Of example, if you just mixed molten aluminum and molten lead, you will find that the two were separated into layers, similar to oil and water.
Commercial and trade alloys usually require more processing and are produced in a controlled environment most often by mixing molten metals. Depending on the characteristics of the used elements, the method for mixing melted metals or metals with nonmetalls varies widely.
During a successful alloy process, factors like melting temperatures of metals, impurities, blending environments and alloy methods are central due to the high variances in their tolerances of heats and gasses.
While elements such as refractory metals are stable at high temperatures, others begin to react with their environment, which may affect their purity and finally the performance of the alloy. Intermediate alloys often need to be formed in such cases in order to allow elements to combine.
The first way to produce an alloy of 95.5% aluminum and 4.5% copper is to produce a 50% blend of the two elements. This mixture is less than aluminum or pure copper and acts as a "hardening alloy" and then is inserted into molten aluminum at the right rate.
Sources: Street, Arthur. & Alexander, W. O. 1944. Metals in the Service of Man. 11th Edition (1998).
