Many people often noticed shiny handles on interior doors, golden chandeliers or candlesticks. All of these elements are made of an alloy called brass. In this article, we will examine its properties and characteristics in more detail, paying particular attention to the L63 brand.
What is brass?
Brass is one of two known copper alloys (the second is bronze). Its basis is copper, in which different amounts of zinc dissolve. As is known, copper has a face-centered cubic crystal lattice (FCC). In turn, pure zinc forms a hexagonal close-packed structure (hcp). Both lattices are incompatible, so in the case of equal atomic concentrations of zinc and copper, the so-called double brass can form. They are characterized by the simultaneous existence of two phases (fcc and hcp solid solutions).
If you pay attention to the table of D. I. Mendeleev, you can see that the zinc in it is at number 30, and copper is at number 29. This proximity of the positions of the elements in the periodic table indicates that they have close atomic radii. This fact allows, in spite of various crystal lattices, to form single-phase solid solutions when the copper content in the alloy exceeds 13.5%, which can be seen from the presented Zn-Cu phase diagram.
Thus, if copper is the main component, then under equilibrium conditions there is only one phase - a solid solution of zinc in fcc copper.
Brand brass L63
This is one of the most common alloys that is cast in our country. It is not difficult to understand what the letter and numbers mean in the brand name: βLβ is actually brass, the number 63 indicates the percentage of the main component, that is, copper. In fact, the reality may differ slightly from the figure indicated. So, in the composition of brass L63, the amount of copper ranges from 62% to 65%, and the zinc in the alloy contains from 34.2% to 37.5%.
Almost all brasses are well machined at low (room) temperatures. The brand in question is no exception. Due to its excellent mechanical properties, a wide range of parts is made from it, including thin sheets, pipes and rods of various thicknesses.
It should also be mentioned that the product of the brand in question is easily polished, therefore, many jewelry items made from it have a golden color and a brilliant shade.
One of the important advantages of L63 brass is its relative cheapness compared to other alloys containing a large amount of copper.
Characteristics L63
As you know, pure copper is a fairly soft material. Its shear strength is 210 MPa. Replacing one third of the copper atoms in the fcc lattice with zinc atoms, as well as a certain heat treatment of brass, increase its shear mechanical strength to 240 MPa.
Another advantage of the characteristics of L63 brass over the properties of copper is its higher hardness while maintaining ductility. Note that in case of improper processing, for example, with insufficient annealing, the second phases based on zinc may appear in the product of the considered brand. Two-phase brass leads to a significant deterioration in mechanical and technological properties. In particular, the alloy becomes brittle and practically loses its plastic characteristics.
The difference between brass and other metals is the absence of sparking during mechanical shock. This property allows the use of L63 in the manufacture of containers for the storage and transportation of flammable substances.
If we talk about the shortcomings of this brand in comparison with pure copper, then we should mention a slight decrease in toughness. In addition, brass L63 is a poor conductor of electricity and heat.
Alloy specific gravity
Recall that density is a quantity equal to the ratio of body mass to the volume that it occupies in space. The density is calculated by the following formula:
Ο = m / V.
In the case of multicomponent alloys in which a simple mixing of chemical elements with a low enthalpy of formation occurs, the following formula can be used to determine their density:
Ο = β i m i / β i (m i / Ο i ).
Where m i and Ο i are the mass and density of the i-th component in the mixture.
Using the written formula, the specific gravity of brass L63 can be calculated. If the expression for Ο is written for two components, then we obtain the following equality:
Ο = Ο zn * Ο cu / (Ο zn + x * (Ο cu -Ο zn )), where x = m zn / (m zn + m cu ).
The parameter x reflects the mass fraction of zinc in the alloy. Since the atomic masses of the brass components are close, it can be assumed that the mass fraction is equal to the atomic one. If for example we take the composition of 63% Cu and 37% Zn and take into account that Ο cu = 8960 kg / m 3 and Ο zn = 7140 kg / m 3 , then we get the value Ο = 8188 kg / m 3 .
Turning to the experimental value of the density of brass L63, we see that it corresponds to 8440 kg / m 3 at room temperature. The discrepancy with the theoretical result is associated with two main factors:
- when the alloy is formed, there is some negative enthalpy of mixing of the components;
- it contains impurities of heavier metals.
Features of heat treatment and corrosion resistance
The product in question melts at a temperature of 906 o C. In the range from 750 o C to 880 o With he still shows good ductility, therefore, can be processed mechanically. An important stage in the production of L63 alloy is annealing, which is performed in the range of 550-650 o C. As a result of this treatment, two main processes occur:
- mechanical stresses are removed;
- metastable phases dissolve with the formation of a single-phase structure.
The presence of mechanical stress is extremely undesirable for L63. It is known that the addition of zinc to copper leads to a significant improvement in its corrosion resistance, therefore, all brasses are sufficiently chemically passive alloys. Over time, they are destroyed only in aggressive environments, for example, in perchloric and nitric acids. However, the presence of stresses in brass structures significantly worsens their corrosion resistance.
Due to the formation of the aforementioned stresses, it is not recommended to subject L63 products to quick cutting.
Areas of use
The considered brand of brass is widely used for the manufacture of tapes, rods, sheets and pipes. A wire is also made from an alloy, which is used for rivets.
Summing up, it should be said that L63 is used wherever it is necessary to carry out significant cold deformations in the production of parts. Clutches, tanks and various decorative elements are made from it.