What is An Alloy? Types of Alloys

What Is An Alloy?

Alloy is a mixture of one or more metals or non-metals (there must be at least one metal) after mixing, melting, and cooling. , aluminum alloy, etc. The alloy is usually referred to as a general term for non-ferrous alloys, such as copper alloys, aluminum alloys, etc. In fact, steel is also an alloy. Ordinary steel is an alloy of iron and carbon, so it is also called carbon steel. In addition to iron and carbon, other elements are added to steel, which is called alloy steel. Another alloy steel added with an element is ternary alloy steel. Such as manganese steel, silicon steel, etc. In addition, the addition of two or more elements is called multi-element alloy steel. Alloy steel is also often named according to its purpose, such as tool steel, high-speed steel, stainless steel, etc.

As an important basic material, alloys are widely used in various fields of industrial manufacturing, including aerospace, energy industry, 5G construction, special manufacturing, etc. Alloys are diverse chemical substances composed of at least two or more metals or metals and non-metals. According to their performance characteristics, they can be divided into superalloys, corrosion-resistant alloys, magnetic alloys, cemented carbides, memory alloys, etc.

Types of Alloys

Cemented Carbide

Cemented carbide is mainly composed of the powder of one or more refractory carbides (tungsten carbide, titanium carbide, etc.), and metal powder (cobalt, nickel, etc.) is added as a binder and is obtained by powder metallurgy alloy. It is mainly used to manufacture high-speed cutting tools and cutting tools for hard and tough materials, as well as cold-working dies, measuring tools, and highly wear-resistant parts that are not impacted and vibrated.


High-temperature alloys, also known as heat-resistant alloys or heat-strength alloys, can work in a high-temperature oxidizing atmosphere of 600~1000 ° C and gas corrosion conditions and have good thermal strength, thermal stability, and thermal fatigue properties.

Superalloys are divided into nickel-based superalloys, iron-based superalloys, and cobalt-based superalloys according to the matrix elements, which are widely used in various fields, especially aviation, aerospace, and power generation equipment, and shipbuilding industries.

Superalloys can be roughly divided into three categories according to basic elements, forming processes, and strengthening methods (the proportion of alloy materials in parentheses is the application range).

Divided according to the basic elements contained in the alloy: divided into iron-based superalloys (14.3%), cobalt-based superalloys (5.7%), and nickel-based superalloys (80%);

Divided according to the alloy manufacturing process: divided into deformed superalloy (accounting for 70%), cast superalloy (accounting for 20%), and new superalloy (powder superalloy);

The alloy strengthening method is divided into solid solution strengthening type, precipitation strengthening type, oxide dispersion strengthening type, and grain boundary strengthening type.

Corrosion-Resisting Alloys

Metal anti-corrosion materials, compared with non-metallic anti-corrosion materials, metal anti-corrosion materials mainly include iron-based alloys (corrosion-resistant stainless steel); nickel-based alloys (Ni-Cr alloy, Ni-Cr-Mo alloy, Ni-Cu alloy, etc. ); active metals.

Memory Alloys

Shape memory alloys refer to a class of metallic materials that return to their original shape at a specific temperature. In general, the material is elastically plastic at relatively low temperatures and returns to its pre-molding shape at a higher temperature. At present, although this shape memory effect is found in many types of alloys, the memory alloys that can generate enough restoring force to fully achieve the original shape, so far only Ti-Ni alloys and copper-based memory alloys. (For example, Cu-Zn-Al sum Cu-Al-Ni).

The Principle of Alloy Synthesis

Often two or more two kinds of metal elements or metal as the basic elements to add other non-metallic elements, through the alloying process (melting, mechanical alloying, sintering, vapor deposition, etc.), and the formation of metal properties of the metal material is called an alloy. But alloys may contain only one metallic element, such as steel. (Steel is a general term for iron alloys with a carbon content between 0.02% and 2.00% by mass)

Taking pure iron as an example, the strength value of pure iron will not change if it is quenched; however, after adding 0.2% carbon element to pure iron and then quenching, the strength value will increase by an order of magnitude. The resistance value of a pure nickel is 6.8 micro ohm·cm. After adding 20% chromium element, the resistance value increases to 100 micro ohm·cm, which can be used for resistance wire heating materials. Another example is pure iron, adding 36% of nickel element, called Invar alloy material, the coefficient of linear expansion at 20 ℃ is 1/9 of iron. Even if the temperature changes, the length remains the same. Therefore, the properties of pure metals are limited. Only when they are combined with other elements can they produce unexpected properties. This kind of material added with other elements and has metallic properties is called alloys.

Here we need to note that alloys are not mixtures in general concepts, and can even be pure substances, such as single-phase intermetallic alloys. The added alloying elements can form solid solutions, and compounds, and produce endothermic or exothermic reactions, thereby changing the metal properties of the substrate.

Alloying elements include manganese, silicon, nickel, titanium, copper, chromium, and aluminum.

The addition of these metals produces specific properties not found in conventional carbon steel.

These elements are added in different ratios/combinations to give the material different effects, such as increased hardness, increased corrosion resistance, increased strength, improved formability, and also, weldability changes.

Common Alloys

Nodular cast iron, manganese steel, stainless steel, brass, bronze, copper, solder, duralumin, 18K gold, and 18K platinum.

Most Commonly Used Alloy Grades

4140: Chromium-Molybdenum Steel

4340: Nickel Chrome-Molybdenum Steel

6150: Chrome-Vanadium Steel

8620: HSLA- Nickel – Chromium-Molybdenum Steel

According to the Structure, the Main Types of Alloys are:

  1. Mixture alloy (eutectic mixture), when the liquid alloy is solidified, the components of the alloy are crystallized separately, such as solder, bismuth cadmium alloy, etc.;
  2. Solid melt alloy, when the liquid alloy solidifies to form a solid solution of the alloy, such as gold and silver alloy;
  3. Metallide alloys are alloys in which the components form compounds with each other, such as brass (β -brass, γ -brass, and ε -brass) composed of copper and zinc, etc.
  4. Alloys have many properties superior to pure metals, so alloys are used in most applications (see ferroalloy, stainless steel).

All Types of Alloys Have the Following Properties:

  1. The melting point of most alloys is lower than that of any of their constituent metals;
  2. The hardness of the alloy is greater than that of any of its components;
  3. The electrical and thermal conductivity of the alloy is lower than that of any component metal. High resistance and thermal resistance materials can be made by using this property of alloys. Materials with special properties can also be made, such as adding 15% chromium and 9% nickel to iron to get corrosion-resistant stainless steel, suitable for the chemical industry.
  4. Some have strong corrosion resistance (such as stainless steel).

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