Brass: alloy composition, characteristics and applications
Brass, which is well known and actively used for many years, is an alloy of copper and zinc. The inventor of this material with a number of unique characteristics is the Englishman James Emerson, who patented it in 1781 year.
Brass metal has good corrosion resistance and high strength
warehouse elements
The basis of brass is copper and zinc. In the most traditional composition of this alloy, copper is contained in quantities 70%, and zinc - 30%. There are brands of technical brass, in which zinc is contained in quantities 48-50 percent. What is characteristic, more 50% zinc, which is used for the production of brass alloys, obtained from wastes of this metal.
Depending on the characteristics of the internal structure, there are brass alpha- and alpha-beta type, which are also called the same- and two-phase.
Their main differences are as follows.
- In the chemical composition of brass alloys, belonging to the alpha type, contained 35% zinc.
- Alpha beta brass (two-phase) on 47-50% consist of zinc. They also contain lead, the number of which does not exceed 6%.
Though, that brass, also created on the basis of copper, looks very similar to some brands of bronze, according to the professional classification it does not apply to bronze alloys. Some types of brass contain tin - the main alloying element of bronze, but it is added in very small quantities, to improve the individual characteristics of the alloy. In addition to tin, the chemical composition of individual brands of brass may contain the following elements, like lead, manganese, iron, nickel and others., Which also improve its properties.
The content of chemical elements in the simple (double) brass (click to enlarge)
Content of chemical elements in lead brass (click to enlarge)
Brass products have a beautiful golden-yellow color, well amenable to polishing and other types of machining. Depending on the brand of alloy, from which the product is made, the latter can be forged in a cold or heated state, but some types of this metal can not be processed by plastic deformation. Though, that brass is characterized by high corrosion resistance, the surface of products from this metal at their long interaction with ambient air is covered with an oxide film and darkens. To avoid discoloration of brass products over time, they are often covered with a protective layer of colorless varnish.
Chemical composition and features of the internal structure
To understand the characteristics of brass, important to understand, what are the properties of chemical elements, of which it consists. Such elements, as mentioned above, there is copper and zinc.
Classification of brass by chemical composition
Copper is one of the first metals, which people began to use for the manufacture of products for various purposes. This element, included in the 11th group of the IV period of the periodic table, has an atomic number 29 and is denoted as Cu (abbreviation of Cuprum). Copper, which is a transition metal, differs in high plasticity and beautiful light golden color. With the formation of the oxide film, the metal acquires no less beautiful yellowish-red hue.
Zinc - the second main element in the chemical composition of brass - is also a metal, which, unlike copper, does not occur in nature in its pure form. Zinc, which has an atomic number 30, is a subgroup of the 2nd group of the IV period of the periodic table. This metal, produce which began in the XII century in India, has high fragility under normal conditions. Without oxide film, which appears on the metal when it interacts with the open air, its surface is light blue. This metal is denoted by the symbol Zn (abbreviation of Zincum).
This is the microstructure of a polished brass surface under 400x magnification
The structure of brass, depending on the content in its composition of the main components may consist of one? - or simultaneously? +? - phases. Such states, which can take the internal structure of the alloy, differ in the following features:
- ?-phase is a solution of copper and zinc, characterized by high stability, in which the base metal molecule (copper) have a face-centered cubic lattice;
- ?+?-phase is also a stable solution, in which copper and zinc are contained in the ratio 3: 2 (in such a solution, copper molecules have a simple unit cell).
Microstructure? +? - brass has less ductility and greater hardness, than structure? -brass
Depending on the heating temperature in brass, the following structural transformations occur.
- When brass is heated to high temperatures the atoms in it? -phase, having a wide range of homogeneity, differ in unregulated location. In this state of heating? The phase of the brass alloy is highly plastic.
- At insignificant heating of a brass alloy (454-468°) It forms a phase, having a designation? ‘. The peculiarity of this structural phase, which has a high hardness and, in accordance, fragility, there is that, that the atoms of copper and zinc in it are arranged in an orderly manner.
Based on all of the above, it is possible to draw a conclusion about that, that brass alloys, whose internal structure is only? Phase (single-phase), have good plasticity, and those, in which present and? Phase (two-phase), are stronger, but not intended for plastic deformation.
The ductility of brass with a two-phase structure can be increased, if heated above temperature, at which it occurs? ‘- transformation (700°). In this state, only one predominates in the structure of the alloy? Phase, in accordance, it has high plasticity. However, even single-phase brass with good ductility may not be processed by plastic deformation. This occurs in the temperature range of their heating to 300-700°, which is called the fragility zone.
The zinc content in brass affects the electrical conductivity of the alloy
To you, what are the mechanical properties of brass of a particular brand, strongly affects the zinc content in its chemical composition. So, if the content of this chemical element is up to 30%, then simultaneously increase in strength, and the ductility of the alloy. Further increase in zinc content leads to that, that brass becomes less ductile (complication? -phases), and then more fragile (formation in the structure of brass? ‘- phases). The strength of brass increases until then, while zinc in its structure will not be 45%, with a further increase in the amount of this element, brass becomes less durable, and less plastic.
production methods
Such an alloy of copper, like brass, well suited to various processing methods. So, from this alloy it is possible to receive various products by forging methods, stamping and drawing, and due to the relatively low melting point and good fluidity in the molten state it is actively used in foundry production.
Pouring brass melt by mold
Brass, the main alloying element in which is zinc, get melting:
- in crucibles, made of refractory material (to heat the crucibles together with the components of the alloy are placed in a shaft or flame furnace);
- in chops (when using this method, melting is performed without the use of crucibles).
That fact should be taken into account when smelting a brass alloy, that zinc during such a procedure will actively evaporate, therefore, the amount of this metal should be calculated with some margin.
Scope
Depending on the quantitative content of the main components, brass can be used for the manufacture of products for various purposes.
The content of the main elements is indicated in the labeling of brass alloys
One of the most common types of deformable brass alloys is tompak, which contains 88-97% copper and no more 10% zinc. The most significant characteristics of alloys of this type are:
- high plasticity;
- high corrosion resistance;
- good antifriction properties.
From the characteristics, which contribute to the high popularity of alloys of this type, it should be noted:
- good weldability with steel and other metals, that allows to use tompak for production of products from the combined materials;
- beautiful golden color is a characteristic, which led to the active use of tompak for the production of artistic products;
- possibility to cover a surface of products from tompak with enamel and a varnish, gild, and use other types of decorative coatings.
This is what a tompak ribbon looks like, from which products are then made, including jewelry
Specialists in the production of tompak use three main formulas of the chemical composition of this alloy, in which copper, zinc, lead and tin can be contained in such proportions:
- 82/18 / 1,5 / 3;
- 82/18/3/1;
- 82,3 / 17,5 / 0 / 0,2.
These formulas, which is remarkable, were bred in the XIX century. They were written by Scottish scientist Andrew Jur.
Areas of application are deformable brass
To get foundry brass, in its composition, except zinc, add 50-81% copper, as well as a number of other elements: aluminum, iron, silicon, lead, manganese, lead. The most significant characteristics, which has such brass, is:
- high corrosion resistance;
- antifriction properties;
- good mechanical characteristics;
- good fluidity in the molten state;
- high resistance to material disintegration.
Areas of application of foundry brass
Due to these characteristics, cast brass alloys are successfully used for the production of products, to mechanical properties, corrosion resistance and accuracy of geometric parameters which are subject to increased requirements.
Automatic brass is used for the production of various products by metal cutting methods, which chemical composition includes:
- 57-75% copper;
- 24,2-42,7% zinc;
- 0,3-0,8% lead.
Automatic brass of the LS59-1 brand is used for production of hardware and decorative elements
Alloys of this type must contain lead, due to which the formation of short and loose chips is provided, that allows to carry out high-speed processing of products from such brass.
Brass of this type is made in the form of sheet material and rods, of which then, using one or another type of machining, produce products for various purposes.
