For many millennia, man has experimented with various metals and received from them increasingly high-strength alloys. For this, a variety of chemical elements were used. The Bronze Age is the era during which the alloy of tin and copper (CuSn 6 ) became popular. What material is this and why was it so popular?
History of Bronze
Thanks to an improvement in the quality of processing of metals such as copper and tin in 3000 BC the Bronze Age began. It is characterized by the active production of an alloy such as bronze, which was used to make tools and jewelry.
In the modern metallurgical industry, in addition to copper and tin, materials such as aluminum, phosphorus, lead, zinc are also used. The name itself comes from the Persian word "berenj", which translates to "copper".
It is known that the first bronze was made of Cu and arsenic and was called arsenic. However, due to its toxicity, it very quickly gave way to tin. Not surprisingly, blacksmiths were very often painted ugly and disfigured. In fact, it was. Prolonged contact with arsenic had a very bad effect on their body. For this reason, the alloy of copper with tin is called bronze, since it is these components that are most often present in it.
Bronze feature
We all know that such a metal as copper is very soft, ductile and absolutely fragile. At the same time, it has a very high electrical and thermal conductivity. The alloy of tin and copper is a material that significantly exceeds the characteristics of these chemical elements separately. In other words, bronze has high hardness, strength, but at the same time it is quite fusible.
The discovery of this alloy played a large role in the metallurgical industry. Despite the fact that many other materials were invented later, even today it is very popular due to its good mechanical properties.
Bronze Resistance to Corrosion
One of the most important properties of an alloy is its corrosion resistance. This is especially true for those compositions in which there is a significant content of manganese and silicon (more than 2%).
It was found that high corrosion resistance is manifested when bronze comes in contact with water (marine and fresh), concentrated alkalis and acids, sulfates and chlorides of light metals, as well as in contact with dry gases (tinless bronzes).
Of course, in general, the corrosion properties of the alloy depend on the alloying elements. Thus, a high lead content reduces the ability to resist corrosion, and nickel increases this property.
Types of Bronze
Alloying elements, which can be part of this alloy, can significantly change its properties, and the type of bronze depends on them. In addition, tin can be replaced by other elements. For example, BrAMC-7-1 can be deciphered as follows: 92% copper, 7% aluminum, 1% manganese. This brand of bronze does not contain tin and, due to this, has high resistance to alternating load. It is used for the manufacture of bolts, screws, nuts and parts for hydraulic installations.
Another example is the tin cast bronze of the BrO10C10 brand. It contains up to 83% copper, 9% tin, 8% lead and up to 0.1% iron, silicon, phosphorus and aluminum. It is designed for parts that operate under high specific pressures, such as plain bearings.
Although bronze is an alloy of tin and copper, in some cases a chemical element such as Sn is not used. Another example of tinless bronze is heat resistant. For its manufacture, only copper 98-99% and cadmium 1-2% are used. An example is the brand BrKd1. This is heat-resistant cadmium bronze with high heat resistance and electrical conductivity. It can be used for manufacturing parts of resistance welding machines, electric motor collectors and other parts operating at high temperatures and requiring good electrical conductivity.
Another type of alloy used to make gaskets in bearings and car bushings is pressure treated tin bronze. The copper and tin alloy contains alloying elements such as lead (4%), zinc (4%), aluminum (0.002%), and iron (0.005%). Steel grade is called BrOTsS4-4-4. Thanks to the percentage of these chemical elements, this alloy can be processed by pressure and cutting. The color of bronze also depends on impurities. So, the less copper the alloy contains, the less pronounced the color: more than 90% is red, up to 80% is yellow, less than 35% is gray-steel.
Bronze processing
As mentioned earlier, the alloy of tin and copper is a fairly durable material. It is difficult to sharpen, cut and pressure work. In general, this is casting material with low shrinkage - about one percent. And even despite the low fluidity and a tendency to segregation, bronze is used for the manufacture of castings with complex configurations. No exception and art casting.
Alloying elements, which are added to the alloy of tin and copper, improve its properties and reduce the price. So, for example, alloying with lead and phosphorus can improve the processing of bronze, and zinc increases its corrosion resistance. For certain purposes, deformed alloys are made. They easily change their appearance when using cold forging.
Application area
Of course, the use of bronze does not lose its popularity in our time. Souvenir products, decorative furnishings, decorations on gates and gates ... In addition, the alloy is used for the manufacture of fittings (handles, hinges, locks) and plumbing fixtures (taps, fittings, gaskets, faucets). In industrial fields, bronze also has extensive areas of use. So, cast alloy is used for the manufacture of bearings, o-rings, bushings.
The widespread use of bronze is particularly affected by its corrosive properties. For this reason, it is used for the manufacture of parts of mechanisms operating in constant contact with water. The high elasticity of the alloy makes it possible to produce springs and parts of instrumentation from it.
Bronze remelting
Of course, each alloy has its advantages and disadvantages. Bronze is an alloy that consists of copper and tin, and therefore it perfectly tolerates any remelting. It can be used several times for completely different purposes. On the other hand, if bronze contains a large amount of impurities, such as magnesium, silicon, aluminum, then during remelting the mechanical properties may decrease.
This is due to the fact that alloying elements that improve the characteristics of bronze oxidize during melting and form refractory oxides, which are located along the boundaries of the crystal lattice. They break the connection between the grains, which makes bronze more fragile.
How to distinguish bronze from brass and copper
One of the most common questions is the difference between this alloy and others, similar in appearance to it. Of course, within the industry and with the help of special reagents, this is quite simple. But what about if you need to determine the material at home?
To begin with, the alloy consists of tin and copper. The masses of these substances in percentage may be different. The more copper, the brighter the color will be, but due to the tin content in the alloy, it will be an order of magnitude heavier than, for example, pure Cu.
If we compare bronze with brass, then the latter has a more yellowish tint. Copper itself is very plastic, but the alloys based on it are quite elastic and hard. You can also determine what material is in front of you by heating. So, in brass, under the influence of high temperature, zinc oxide is released and the product acquires an ashy "coating". But bronze will not change its properties when heated.
Works of art
Quite often you can find various bronze figurines and figurines. Many works of art were created in ancient times and in the Middle Ages.
Alloys containing copper and tin are used for the manufacture of:
- Fences and gates that turn out to be not only incredibly beautiful, but also durable.
- Elements of staircases.
- Souvenir products and sculptural compositions.
- Decorative lighting fixtures: sconces and chandeliers.
- Items for interior decoration.
In order to cast the necessary composition, create a special model of wood, plaster or polymeric materials - the so-called molding. The cavities of this figure are filled with clay and removed after casting. After manufacturing, the surface can be coated with gilding, a layer of nickel, chromium or silver.
It is very important to note that, as a rule, an alloy of tin and copper without alloying elements is used to make works of art. This is due to the fact that the more such components are present in bronze, the greater its shrinkage, which negatively affects the quality and shape of the product.