Chemical composition of brass: alloys, their compositions, types and differences
Brass is an alloy based on zinc and copper. The percentage of zinc in the alloy may be 5 — 45%. Zinc, unlike copper, cheaper, that is why its introduction into the composition not only increases the technological, antifriction and mechanical properties of the alloy, but also reduces its cost.
Properties of brass
Brass alloys are excellent for pressure treatment. Mechanical performance is quite high, but here is satisfactory corrosion resistance. If you compare the features of brass with bronze, then its antifriction properties, corrosion resistance, strength is lower. Alloys are not very stable in salt water, in the air, solutions of most organic acids and carbon dioxide solutions.
Brass, unlike copper, has better corrosion resistance. But with increasing temperature, the corrosion rate increases. Moreover, this process is noticeable in products with thin walls. May cause corrosion: high humidity, traces of sulfur dioxide and ammonia in the air. To prevent this phenomenon, the products of this composition after processing are subjected to low-temperature firing.
Almost all alloys do not become brittle when the temperature decreases and remain elastic, which allows you to use them as an excellent structural material. Due to the higher recrystallization temperature, unlike copper, at elevated temperatures, the creep of brass is lower. At temperature 300-600 the property of fragility appears due to that, which are insoluble at low addition temperatures (example: bismuth, lead) create fragile layers between the crystals. As the temperature increases, the toughness decreases. Unlike copper, the thermal and electrical conductivity properties of brass are worse.
The composition of brass in percentage
The main components are zinc and copper, used in ratios 30% and 70% in accordance.
More 50% zinc, which is used in the manufacture of brass, is made from recycling. Technical alloys of brass are made on 47-50% zinc. There are alpha and beta-brass in composition:
- Two-phase compositions are composed of 48-50% zinc and contain less 5% lead.
- Single-phase alpha compositions have about 30% zinc.
Chemical composition
Brass is made of copper and zinc. It is often compared to bronze, since the alloy of brass and bronze combines the same component - copper. Brass, in composition differs from bronze, has as the second component not tin, and zinc.
Zinc is a chemical component of the secondary subgroup of the second group of the fourth period of the periodic table.. Under normal conditions, quite fragile transition material of bright blue color (in the open air is covered with a small layer of zinc oxide and darkens). In nature, as a separate metal, zinc does not exist.
Copper is a chemical component of the eleventh group of the fourth period of the periodic table.. It is a plastic transition material of bright golden color (with the appearance of the oxide layer, the copper becomes reddish-yellow).
Due to zinc and copper (except the main thing ?-solution) a whole list of electronic stages of the type appears ?, ?, ?. Usually, has a composition of brass ?- or ?+?‘Phases:
- ?-phase - a stable material of copper and zinc with face-centered crystalline copper cubic lattice.
- ?'-Phase - a structural material based on the chemical combination of CuZn with the ratio 3/2 and the elementary and simplest cell.
Dependence on heat treatment:
- If the temperature is high, then ?-the phase has a chaotic arrangement of atoms and an increased volume of homogeneous composition. In this state, the phase becomes quite plastic, if the temperature is less 453-469 C, then the atomic structure of copper and zinc finds order and is indicated, as ?’.
- ?’Is more fragile and tough, ?-phase contains an electronic combination of Cu5Zn8.
Compositions with one phase are characterized by high plasticity; ?’-Phase is less ductile and more durable.
Separation taking into account the content of zinc alloy:
-
When the alloy of brass contains up to 35% zinc, plasticity also increases at the same time, hardness. Then the plasticity decreases, initially due to sealing ? - rigid composition. Then there is an instantaneous decrease, this is due to being in the fragile ?‘-Phase. Then the hardness increases to the level of zinc no more 40%. Then it decreases sharply.
- Many formulations are excellent for pressure treatment. Single-phase composition is especially characterized by its plasticity. Brass changes its structure at low and high temperatures. Although in temperature conditions 400-700 C "fragile zone" appears. Deformation under these temperature conditions does not occur.
- Two-phase alloys are quite elastic when heated above the phase temperature ?'-transformation (above 700 C). To increase chemical resistance and technical characteristics, they often add additional components, example: manganese, aluminum, silicon, nickel and so on.
Brass production
Brass is excellent for forging, malleable, quite viscous, takes various forms under the blow of a hammer, stamped into various parts or stretched into wire. The alloy is relatively malleable and melts at temperatures less than the melting of copper.
The manufacturing process is in progress:
- In crucibles, made of fire-resistant clay. The crucibles are heated in flames or shaft furnaces.
- In chops.
When mixing zinc and copper composition is poured into pre-prepared sand molds. Some of the zinc evaporates, what to keep in mind when forming a metal alloy.
Derivatives of brass
Tompak is a type of deformed alloy. Contains zinc and copper 2%-13% and 87-98% in accordance.
Tompak is different:
- reduced friction force;
- rust resistance;
- high elasticity.
Copper compounds, consisting of 11-22% zinc, are called semi-mounds.
Tompak is excellent for welding with stainless steel and other precious metals. Tompak is used to make a combined composition of brass and steel. Thanks to the golden color of tompak make accessories, various medals and works of art. Tompak is excellent for enameling, gilding and pressure treatment at low and high temperatures.
Foundry brass - used for the manufacture of shaped products and semi-finished products by casting. Has 51-80% copper. Used as additional elements: aluminum, silicon, manganese, iron, lead and tin. The main differences:
- has resistance to friction with other elements;
- reduced tendency to decay of elements;
- does not rust;
- easy to handle due to the liquid consistency;
- excellent mechanical performance.
Most often, foundry brass is used for mass production:
- worm screws;
-
fittings;
- reinforcement elements;
- details, corrosion resistant;
- nuts of clamping bolts;
- separators;
- bushings;
- details, which are operated at temperatures above 250C;
- bearings.
Automatic brass is a lead alloy. It has such a composition:
- 24,3-42,8% - zinc;
- 56-76% - copper;
- 0,4-0,9% - lead.
The addition of lead during machining promotes the appearance of loose and short chips, which reduces wear of the separating mechanism and gives the chance to apply high-speed processing of details.
The mechanical characteristics of automatic brass directly depend on its physical state and components:
- cold-worked;
- soft.
This type of alloy is made in the form:
- smug;
- tapes;
- letters;
- rods.
Thus from letters do:
- details for watches;
- bolts;
- nuts and other mass-produced items.
How to distinguish a brass alloy from bronze
Distinguish brass from bronze and, exept this, you can find out the exact composition only in a chemical laboratory (example, using spectroscopic analysis). Unfortunately, at home (Moreover, if you can not scratch or otherwise deform the product) the range of possibilities is rather limited. However, there is an algorithm, which shows albeit not very accurate, but still results.
You will need it:
- calculator;
- exact scales;
- transparent container with water;
- samples of brass and bronze with chips;
- microscope or magnifying glass.
Start with visual analysis. You need to thoroughly clean the product and place it in the sun. Usually bronze is darker than brass, with, if you consider color, then bronze goes into the "red" spectrum (from red to brown), and brass in "yellow", sometimes even to white. But this method is not very inaccurate, so go to step two.
Analyze the composition for density. You will need a clear container of water and accurate scales. Lowering the product into the water, find out the volume, then determine the mass. Density is the ratio of the mass of an object to its volume, convertible to kg / cubic meter. m. Most often, bronze is denser than brass, while the dividing line is on the indicators 8700 kg / cu. m. so, 8400-8700 kg / cu. m - most likely, brass. 8750-8900 - likely, bronze.
And in the end, warehouse structure. I must say, that samples are needed here - objects, where the composition can be accurately identified and brass, bronze, and the samples must be chipped.
A strong magnifying glass or microscope will be needed for analysis. The analysis is placed in the field of view of both the sample and the subject of analysis. What you need to pay attention to? On the structure of the warehouse - namely, his grain. Usually bronze has coarser and larger grains, unlike brass.
