It must be borne in mind that these ratios correspond to the equilibrium conditions that take place when diffusion processes are complete.
Along with unlimited solutions, a number of metals and elements form limited solid solutions with each other, when solutions are formed only in a certain concentration range, and at higher concentrations other structural formations are formed.
The specificity of limited solid solutions is that the region of solid solutions adjoins the pure components (small concentrations of the alloying element) on the state diagrams. These solid solutions retain the structure of pure metals, and other structural formations on the state diagram, called intermediate phases or intermetallic compounds, have a structure that differs from the base and alloying metal. On fig. 13, as an example, a double state diagram of aluminum - magnesium is shown (left side of the diagram). The limiting solubility of magnesium in aluminum at a temperature of 449°C is 17.4% (by mass), and the minimum solubility at a temperature of 20°C is only 1.4% Mg (for the equilibrium state). Only in this range does magnesium form a solid solution with aluminum - a. Above the marked limiting concentrations of the solubility of magnesium in aluminum, an intermediate phase (intermetallic compound) of approximate chemical composition appears.
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Rice. 13. Left side of the state diagram of Al-Mg |
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Rice. 14. State diagram of Al-Si |
Intermetallic compounds, as a rule, increase the hardness and reduce the ductility of the alloy.
The eutectic state diagram is formed by two metals that form mutual solutions in the liquid state, but are practically insoluble in the solid state. In the solid state, the structure of such alloys is a eutectic - a mechanical mixture of grains of two metals.
An example of a eutectic-type diagram is the aluminium-silicon phase diagram. Such a system of alloys is characterized by the presence of a purely eutectic composition - for an Al-Si alloy, the eutectic composition is 11.7% Si + Al - the rest.
Eutectic alloys have a strictly defined solidus temperature; in particular for Al-Si alloys, the solidus temperature is 588°C.
It is at this temperature that the end of solidification occurs at all silicon concentrations. A purely eutectic alloy of this system has a silicon concentration of 11.7%, its solidification occurs at a constant temperature of 588°C (without a solidification interval). Cast alloy Ak12 is considered a purely eutectic alloy. Alloys with a silicon concentration of less than 11.7% Si are hypoeutectic and have the structure: a + eutectic, where a is a solid solution of silicon in aluminum, has a very low silicon concentration and is almost pure aluminum. Alloys with a silicon concentration of more than 11.7% are hypereutectic and are characterized by the structure: silicon + eutectic. Hypoeutectic and hypereutectic alloys solidify in the temperature range, but at the same solidus temperature of 588°C.
Significantly less use in technology are alloys characterized by state diagrams of the peritectic type; as well as alloys with phase diagrams having chemical compounds.
In addition, most alloys are multicomponent, i.e. contain not one, but several alloying elements. In this case, the state diagram cannot be represented by a flat image. So alloys of three elements are represented by a phase diagram in a three-dimensional image: an equilateral triangle sets the composition of the alloys, and the perpendiculars at the corners to the plane of the triangle reflect the temperature value; phase transformations in a three-component alloy are represented by surfaces above the plane of an equilateral triangle. For a flat image, when analyzing such diagrams, polythermal sections (section by a vertical plane) and isothermal sections (section by a horizontal plane) are used. However, most often a multicomponent alloy is considered as a two-component alloy with a flat representation of the phase diagram. Alloying elements in their effect on phase transitions are taken into account by introducing reduction factors to the main alloying element.
On fig. the phase diagram of Al—Mg is shown. The middle part of the diagram is shown enlarged.
The β(Al3Mg2), γ(Al12Mgl7), ζ(Al52Mg48), ε(Al30Mg23) phases are formed in the system. Phases β and γ melt congruently at temperatures of 453 and 460°C, respectively. The ε and ζ phases are formed by peritectic reactions at temperatures of 450 and 452°C, respectively.
There are three eutectic equilibria in the system: L ↔Mg+ γ at 438°C, L ↔(A1) + β at 450°C, L ↔ε + β at 448°C, as well as two eutectoid equilibria ε↔ β + ζ at -428 °C and ζ ↔β + γ at 410 °C.
The solubility of Mgv (A1) has been studied in many works.
Solubility Mg:
% (at.) ......................
% (by mass) ..............
The maximum solubility of Mg in (A1) was determined to be 16.5% (at.), as well as in a number of other works where the X-ray analysis method was not used. The data on the solubility of A1 in (Mg) obtained in different studies also differ. The most likely values are as follows:
Solubility Al:
% (at.) .....................
% (by mass) ..............
Sources:
- State diagrams of binary and multicomponent systems based on iron. Bannykh O. A., Budberg P. B., Alisova S. P. et al. Metallurgy, 1986
- Double and multicomponent systems based on copper. ed. Shukhardina S.V. Science, 1979
- State Diagrams of Binary Metallic Systems ed. Lyakisheva N.P. Mechanical engineering, 1996-2000
Aluminum is one of the most important materials used in the electronics industry, both in its pure form and in numerous types of alloys based on it. Pure aluminum has no allotropic modifications, has high thermal and electrical conductivity, which are 62-65% of those for copper. The melting point of aluminum is 660 °C, the boiling point is 2500 °C. The hardness of pure aluminum is 25 HB Brinell. Aluminum is easily processed by cutting, drawing, pressure.
Upon contact with air, a non-porous protective oxide film approximately 2 nm thick (20 A) forms on the aluminum surface, protecting it from further oxidation. Aluminum has low corrosion resistance in alkali solutions, hydrochloric and sulfuric acids. Organic acids and nitric acid do not act on it.
The industry produces several grades of aluminum: special purity, high purity and technical purity. High purity aluminum grade A999 contains no more than 0.001% impurities; high purity grades A995, A99, A97 and A95, respectively - no more than 0.005; 0.01; 0.03 and 0.05% impurities; technical purity grade A85 - no more than 0.15% impurities.
In electronics, pure aluminum is used in the production of electrolytic capacitors, foils, and also as targets in the formation of aluminum conductive tracks of microelectronic devices using thermal, ion-plasma and magnetron sputtering methods.
Of greatest interest to electronics are alloys based on the "aluminum-copper" and "aluminum-silicon" systems, which make up two large groups of wrought and cast alloys used as structural materials.
On fig. 2.7 shows the equilibrium diagram of the state of the "aluminum - copper" system from the side of aluminum. The eutectic alloy in this system contains 33% copper and has a melting point of 548°C. With an increase in the content of intermetallic in the alloy, the strength of the alloy increases, but its machinability deteriorates. The solubility of copper in aluminum at room temperature is 0.5% and reaches 5.7% at the eutectic temperature.
Alloys with a copper content of up to 5.7% can be transferred to a single-phase state by quenching them from a temperature above the line B.D. At the same time, the hardened alloy has sufficient ductility with moderate strength and can be processed by deformation. However, the solid solution formed after quenching is nonequilibrium, and the processes of precipitation of intermetallic compounds occur in it, accompanied by an increase in the strength of the alloys. At room temperature, this process takes 4-6 days and is called the natural aging of the alloy. The acceleration of the aging process of the material is ensured by holding it at an elevated temperature, this process is called artificial aging.
Rice. 2.7. State diagram of the aluminum-copper system Other group aluminum alloys, called aluminum casting alloys or silumins, are alloys based on the aluminum-silicon system. The state diagram of this system is shown in fig. 2.8.
Rice. 2.8.
The eutectic alloy contains 11.7% silicon and has a melting point of 577°C. This system does not form intermetallic compounds. Eutectic alloys have good casting and satisfactory mechanical properties, which improve with the introduction of up to 1% sodium compounds into the alloy.
On the basis of aluminum, a large number of various alloys are produced, characterized by low density (up to 3 g / cm 3), high corrosion resistance, thermal conductivity, electrical conductivity, heat resistance, strength and ductility at low temperatures, and good light reflectivity. Protective and decorative coatings are easily applied to products made of aluminum alloys, they are easily machined and welded by resistance welding.
Aluminum alloys, along with the base metal aluminum, may contain one or more of the five main alloying components: copper, silicon, magnesium, zinc and manganese, as well as iron, chromium, titanium, nickel, cobalt, silver, lithium, vanadium, zirconium, tin , lead, cadmium, bismuth, etc. Alloying components completely dissolve in liquid aluminum at a sufficiently high temperature. Solubility in the solid state with the formation of a solid solution for all elements is limited. Undissolved particles either form independent, most often hard and brittle crystals in the alloy structure, or are present in the form of pure elements (silicon, tin, lead, cadmium, bismuth), or in the form of intermetallic compounds with aluminum ( A 2 Cu; Al 3 mg2 ; Al 6 Mn; AlMn; Al 3 Fe; A 7 Cr; Al 3 Ti ; Al3Ni; AlLi).
In alloys with two orthree alloying components, intermetallic compounds are part of double ( mg2 Si, Zn 2 , Mg), ternary [ α (AlFeSi )] and more complex phases.
The resulting solid solution and the presence of heterogeneous structural components determine the physical, chemical, and technological properties of the alloys. The influence of alloying on the structure of alloys is described by a phase diagram, which determines the nature of the course of the solidification process, the composition of the resulting phases, and the possibility of various transformations in the solid state. On fig. 1 - 9 state diagrams of binary and ternary aluminum alloys are considered.
Alloy Al-Cu systems. It can be seen from the diagram that when the copper content is from 0 to 53%, there is a simple eutectic system Al(α ) - Al 2 Cu(θ) with eutectic at a temperature of 548°C and a content of 33% Cu. Maximum solubility (at eutectic temperature) of copper in α -solid solution - 57%. The solubility of copper decreases with decreasing temperature and at a temperature of 300°C is 0.5%. Undissolved copper is in equilibrium in the form of the A 2 Cu phase. At medium temperatures, as a result of the decomposition of a supersaturated solid solution, metastable intermediate phases are formed (θ " and θ ").
Alloy Al systems -Si. The system is purely eutectic, existing at a temperature of 577 ° C and a content of 12.5% Si. In α -solid solution at this temperature dissolves 1,6 % Si . The crystallization of eutectic silicon can be affected by a slight addition of sodium. In this case, a supercooling dependent on the solidification rate and a displacement of the eutectic point occur with a corresponding refinement of the eutectic structure.
Alloy systemic Al-Mg. The range of magnesium content in the alloy from 0 to 37.5% is eutectic. The eutectic exists at a temperature of 449°C and a content of 34.5% mg . The solubility of magnesium at this temperature is maximum and is 17.4%. At a temperature of 300°C in α -solid solution dissolves 6.7% Mg; at 100°C - l,9% Mg . Undissolved magnesium is found in the structure most often in the formβ-phase (Al 3 Mg 2 ).
Alloy Al-Zn systems. The alloys of this system form a eutectic system at a temperature of 380°C with a zinc-rich eutectic at a content of 97% Zn . The maximum solubility of zinc in aluminum is 82%. In the area of α -solid solution below the temperature of 391°C there is a gap. enriched with zinc α -phase at a temperature of 275°C decomposes with the formation of a eutectic mixture of aluminum with 31.6% Zn and zinc with 0.6% Al. Further, the solubility of zinc decreases and at a temperature of 100°C it is only 4%.
Alloy State Diagrams Al-Mn systems, Al - Fe indicate the existence of eutectics at very low concentrations of alloying elements. With the exception of manganese, the solubility of elements in the solid state is negligible, for example, iron< 0,05%.
in alloys Al-Ti systems (see fig. 1.14), Al- C rthe solubility of the elements is tenths of a percent.
AT alloy Al-Pb systems As the temperature decreases, the components separate already in the melt with the formation of two liquid phases. Solidification begins almost at the melting temperature of aluminum and ends at the melting temperature of the alloying element (monoeutectic crystallization).
Alloy Al - Mg - Si systems consists of two triple eutectics. Triple eutectic Al - Mg 2 S i - Si containing 12% Si and 5% Mg , melts at 555°C. eutectic Al - Mg 2 Si-AlbMg2 with a melting point of 451°C almost does not differ from the binary system Al - Al 3 Mg2 . The liquidus line connecting both triple eutectic points passes through a maximum at a temperature of 595°C exactly along the quasi-binary cross section (8.15% Mg and 4.75% Si ). Due to the excess of magnesium (in relation to mg 2 Si ) silicon solubility in α -solid solution is greatly reduced. Alloys Al - Mg , especially foundries, contain a few tenths of a percent of silicon and therefore belong to a partial system Al - Mg 2 Si - Al 3 Mg 2 .
Alloy Al-Cu-Mg systems. The state diagram of this system shows that along with double phases A 3 Mg 2 (β ) and Al 2 Cu(θ) in equilibrium with a solid solution α can contain two triple phases S and T. Behind the peritectic transformation at a high copper content, a cross section close to the quasi-binary one is formed A l-S (eutectic temperature 518°C) and partial eutectic region Al - S - Al 2 Cu (eutectic temperature 507°C). Magnesium-rich phase T ( Al 6 Mg 4 Cu ) arises on the basis of the phase S as a result of a peritectic four-phase reaction at a temperature of 467°C. At a temperature of 450°C, a subsequent peritectic four-phase reaction occurs, according to which the T phase is converted into β.
Alloy Al-Cu-Si systems. The state diagram of the alloy shows that aluminum forms with silicon and the A 2 Cu phase a simple ternary eutectic partial system (eutectic temperature 525°C). The joint presence of copper and silicon does not affect their mutual solubility in α -solid solution.
Alloy Al-Zn-Mg systems. Double phases are involved in the construction of the aluminum corner of the system Al 3 Mg 2 , MgZn 2 and ternary phase T, corresponding to the average chemical composition Al 2 Mg 3 Zn 3 . Cross sections Al - MgZn 2 and Al -T remain quasi-binary (eutectic temperature 447°C). In a partial area Al-T-Zn at a temperature of 475°C, a peritectic four-phase reaction takes place, according to which the T phase is transformed into the phase MgZn 2 . Subsequently, during the passage of a four-phase reaction at a temperature of 365°C from the phase MgZn2 at a high zinc content, a phase is formed MgZn 5 , which, together with aluminum and zinc, crystallizes by eutectic reaction at a temperature of 343°C.
In aluminum-based alloys, alloying with the main components is provided in such a way that their total content is below the maximum solubility. The exception is silicon, which, due to the favorable mechanical properties of the eutectic, is used in eutectic and hypereutectic concentrations.
Impurities and additives can modify the phase diagram only slightly. These elements are most often slightly soluble in solid solution and form heterogeneous precipitates in the structure.
Due to incomplete alignment of the concentration within the primary crystals of the aluminum solid solution during its solidification, eutectic regions may appear in the structure at a concentration below the maximum solubility, especially in the cast state. They are located along the boundaries of primary grains and interfere with machinability.
Since alloying additives dissolve in solid solution, heterogeneous structural components can be eliminated by prolonged heating at high temperatures (homogenization) by diffusion. During hot deformation, brittle precipitates along the grain boundaries are mechanically destroyed and distributed in the structure in a line mode. This process is characteristic of the transformation of a cast structure into a deformed one.
Aluminum alloys according to the method of processing are divided into wrought and cast.
New aluminum-based slabs are currently being developed to further expand the scope of these materials. So, for the project of an environmentally friendly aircraft operating on liquid hydrogen (its temperature is -253 ° C), a material was required that does not become brittle at such low temperatures. The O1420 alloy based on aluminum alloyed with lithium and magnesium, developed in Russia, satisfies these requirements. In addition, due to the fact that both alloying elements in this alloy are lighter than aluminum, it is possible to reduce the specific gravity of the material, and, accordingly, the flight mass of the machines. Combining the good strength inherent in duralumin and low density, the alloy also has high corrosion resistance. Thus, modern science and technology is moving towards the creation of materials that combine the maximum possible set of useful qualities.
It should also be noted that at present, along with the traditional alphanumeric marking, there is a new digital marking of aluminum alloys - see fig. 3 and table. ten.
Picture 3 - The principle of digital marking of aluminum alloys
Table 10
Examples of designations using the new markings
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alloying elements |
Marking |
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Traditional | ||
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Al (pure) | ||
Bibliography
1. Kolachev B.A., Livanov V.A., Blagin V.I. Metal science and heat treatment of non-ferrous metals and alloys. M.: Metallurgy, 1972.-480 p.
2. Lakhtin Yu.M., Leontieva V.P. Materials Science. M.: Mashinostroenie, 1990.-528 p.
3. Gulyaev A.P. Metal science. M.: Metallurgy, 1986.-544 p.
4. Encyclopedia of inorganic materials. Volume 1.: Kyiv: Editor-in-Chief of the Ukrainian Sov. Enc., 1977.-840 p.
5. Encyclopedia of inorganic materials. Volume 2.: Kyiv: Editor-in-Chief Ukrainian Sov. Enc., 1977.-814 p.
6. Materials science and technology of materials. Fetisov G.P., Karpman M.G., Matyunin V.M. etc. M. - V.Sh., 2000.- p.182
Attachment 1
State diagram of Al-Mg (a) and dependence of mechanical properties
alloys from magnesium content (b)
Annex 2
state diagramAl - Cu:
dashed line - hardening temperature of alloys
Appendix 3
state diagramAl – Si(a) and the influence of silicon
on the mechanical properties alloys
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ………four
1 Aluminium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . …...four
2 Alloys based on aluminum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . …...5
2.1 Wrought aluminum alloys,
not hardened by heat treatment. . . . . . . . . . . . . . . . . . . . . . . . .......6
2.2 Wrought aluminum alloys,
hardened by heat treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . .......7
2.3 Cast aluminum alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......eleven
2.4 Alloys produced by powder metallurgy………...……..…..14
Conclusion………………………………………………….………………..……..16
References……………………….…………………………………………...17
Attachment 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . …. . . . . . . . . . . . . . . . . . . ….19
Annex 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . ….. twenty
Annex 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . ….21
Department of Theoretical Foundations of Materials Science
