Aluminum Description: Aluminum does not have polymorphic transformations, it has a face-centered cube lattice with a period a=0.4041 nm. Aluminum and its alloys lend themselves well to hot and cold deformation - rolling, forging, pressing, drawing, bending, sheet stamping and other operations.
All aluminum alloys can be joined by spot welding, and special alloys can be welded by fusion and other types of welding. Wrought aluminum alloys are divided into hardened and non-hardened by heat treatment.
All properties of alloys are determined not only by the method of obtaining a semi-finished workpiece and heat treatment, but mainly by the chemical composition and especially the nature of the phases - hardeners of each alloy. The properties of aging aluminum alloys depend on the types of aging: zone, phase or coagulation.
At the stage of coagulation aging (T2 and T3), corrosion resistance increases significantly, and the most optimal combination of strength characteristics, stress corrosion resistance, exfoliating corrosion, fracture toughness (K 1s) and plasticity (especially in the high direction) is provided.
The condition of the semi-finished products, the nature of the plating and the direction of cutting the samples are indicated as follows - Symbols for rolled aluminum:
M - Soft, annealed
T - Hardened and naturally aged
T1 - Hardened and artificially aged
T2 - Hardened and artificially aged for higher fracture toughness and better stress corrosion resistance
ТЗ - Hardened and artificially aged according to the regime that provides the highest resistance to corrosion under stress and fracture toughness
N - hard-worked (hard-working of sheets of alloys such as duralumin about 5-7%)
P - Semi-hardened
H1 - Heavily hard-worked (hard-working of sheets approximately 20%)
Chamber of Commerce - Hardened and naturally aged, increased strength
GK - Hot-rolled (sheets, plates)
B - Technological cladding
A - Normal plating
UP - Thick cladding (8% per side)
D - Longitudinal direction (along the fiber)
P - Transverse direction
B - Altitude direction (thickness)
X - Chord direction
R - Radial direction
PD, DP, VD, VP, XR, RX - The direction of cutting samples used to determine the fracture toughness and growth rate of a fatigue crack. The first letter characterizes the direction of the sample axis, the second - the direction of the plane, for example: PV - the axis of the sample coincides with the width of the semi-finished product, and the plane of the crack is parallel to the height or thickness.
Analysis and sampling of aluminum: Ores. Currently, aluminum is obtained from only one type of ore - bauxite. The commonly used bauxite contains 50-60% A 12 O 3,<30% Fe 2 О 3 , несколько процентов SiО 2 , ТiО 2 , иногда несколько процентов СаО и ряд других окислов.
Samples from bauxite are taken according to general rules, paying special attention to the possibility of moisture absorption by the material, as well as to the different proportions of large and small particles. The mass of the sample depends on the size of the tested delivery: from every 20 tons, at least 5 kg must be taken into the total sample.
When sampling bauxite in cone-shaped piles, small pieces are broken off from all large pieces weighing >2 kg, lying in a circle with a radius of 1 m, and taken into a shovel. The missing volume is filled with small particles of material taken from the side surface of the test cone.
The selected material is collected in tightly closed vessels.
All sample material is crushed in a crusher to a particle size of 20 mm, poured into a cone, reduced and again crushed to a particle size of<10 мм. Затем материал еще раз перемешивают и отбирают пробы для определения содержания влаги. Оставшийся материал высушивают, снова сокращают и измельчают до частиц размером < 1 мм. Окончательный материал пробы сокращают до 5 кг и дробят без остатка до частиц мельче 0,25 мм.
Further preparation of the sample for analysis is carried out after drying at 105 ° C. The particle size of the sample for analysis should be less than 0.09 mm, the amount of material is 50 kg.
Cooked bauxite samples are very prone to segregation. If samples consisting of particles of size<0,25 мм, транспортируют в сосудах, то перед отбором части материала необходимо перемешать весь материал до получения однородного состава. Отбор проб от криолита и фторида алюминия не представляет особых трудностей. Материал, поставляемый в мешках и имеющий однородный состав, опробуют с помощью щупа, причем подпробы отбирают от каждого пятого или десятого мешка. Объединенные подпробы измельчают до тех пор, пока они не будут проходить через сито с размером отверстий 1 мм, и сокращают до массы 1 кг. Этот сокращенный материал пробы измельчают, пока он не будет полностью проходить через сито с размером отверстий 0,25 мм. Затем отбирают пробу для анализа и дробят до получения частиц размером 0,09 мм.
Samples from liquid melts of fluorides used in the electrolysis of aluminum melt as electrolytes are taken with a steel ladle from the liquid melt after removal of the solid accretion from the surface of the bath. The liquid sample of the melt is poured into the mold and a small ingot with dimensions of 150x25x25 mm is obtained; the entire sample is then ground to a laboratory sample particle size of less than 0.09 mm...
Aluminum melting: Depending on the scale of production, the nature of casting and energy capabilities, aluminum alloys can be melted in crucible furnaces, resistance electric furnaces, and electric induction furnaces.
The smelting of aluminum alloys should ensure not only the high quality of the finished alloy, but also the high productivity of the units and, in addition, the minimum cost of casting.
The most advanced method of melting aluminum alloys is the method of induction heating with industrial frequency currents.
The technology for the preparation of aluminum alloys consists of the same technological stages as the technology for the preparation of alloys based on any other metals.
1. When carrying out melting on fresh ingot metals and ligatures, aluminum is first loaded (in whole or in part), and then the ligatures are dissolved.
2. When carrying out melting using a preliminary ingot alloy or ingot silumin in the charge, ingot alloys are first loaded and melted, and then the required amount of aluminum and master alloys are added.
3. In the case when the charge is made up of waste and ingot metals, it is loaded in the following sequence: primary aluminum ingot, defective castings (ingots), waste (first grade) and refined remelting and ligatures.
Copper can be introduced into the melt not only in the form of an alloy, but also in the form of electrolytic copper or waste (introduction by dissolution).
Aluminum and stainless steel may look similar, but they are actually quite different. Keep these 10 differences in mind and guide them as you select the type of metal for your project.
- Strength to weight ratio. Aluminum is usually not as strong as steel, but it is also much lighter. This is the main reason why airplanes are made of aluminum.
- Corrosion. Stainless steel is made up of iron, chromium, nickel, manganese and copper. Chromium is added as an element to provide corrosion resistance. Aluminum has a high resistance to oxidation and corrosion, mainly due to a special film on the metal surface (passivation layer). When aluminum oxidizes, its surface becomes white and sometimes pitted. In some extreme acidic or alkaline environments, aluminum can corrode at a catastrophic rate.
- Thermal conductivity. Aluminum has a much better thermal conductivity than stainless steel. This is one of the main reasons why it is used for automotive radiators and air conditioners.
- Price. Aluminum is usually cheaper than stainless steel.
- Manufacturability. Aluminum is quite soft and easier to cut and deform. Stainless steel is a more durable material, but it is harder to work with, as it is more difficult to deform.
- Welding. Stainless steel is relatively easy to weld, while aluminum can be problematic.
- thermal properties. Stainless steel can be used at much higher temperatures than aluminum, which can become very soft as early as 200 degrees.
- electrical conductivity. Stainless steel is a really poor conductor compared to most metals. Aluminum, on the other hand, is a very good conductor of electricity. Due to its high conductivity, low mass and corrosion resistance, high voltage overhead power lines are usually made of aluminum.
- Strength. Stainless steel is stronger than aluminium.
- Impact on food. Stainless steel is less likely to react with food. Aluminum can react with products that can affect the color and smell of the metal.
Still not sure which metal is right for your purposes? Contact us by phone, email or come to our office. Our account managers will help you make the right choice!
Currently, the most common illegal armed formations systems on the Russian market can be divided into three large groups:
- systems with a sub-facing structure made of aluminum alloys;
- systems with a substructure made of galvanized steel with a polymer coating;
- systems with stainless steel substructure.
The best strength and thermal performance, of course, have sub-facing structures made of stainless steel.
Comparative analysis of physical and mechanical properties of materials
*Properties of stainless steel and galvanized steel differ slightly.
Thermal and strength characteristics of stainless steel and aluminum
1. With 3 times lower load-bearing capacity and 5.5 times higher thermal conductivity of aluminum, the aluminum alloy bracket is a stronger "cold bridge" than the stainless steel bracket. An indicator of this is the coefficient of thermal uniformity of the building envelope. According to research data, the coefficient of thermal uniformity of the enclosing structure when using a stainless steel system was 0.86-0.92, and for aluminum systems it is 0.6-0.7, which makes it necessary to lay a large thickness of insulation and, accordingly, increase the cost of the facade .
For Moscow, the required resistance to heat transfer of walls, taking into account the coefficient of thermal uniformity, is 3.13/0.92=3.4 (m2.°C)/W for a stainless bracket, and 3.13/0.7= for an aluminum bracket 4.47 (m 2 .°C) / W, i.e. 1.07 (m 2 .°C) / W above. Hence, when using aluminum brackets, the thickness of the insulation (with a thermal conductivity coefficient of 0.045 W / (m. ° C) should be taken almost 5 cm more (1.07 * 0.045 = 0.048 m).
2. Due to the greater thickness and thermal conductivity of aluminum brackets, according to calculations carried out at the Research Institute of Building Physics, at an outdoor temperature of -27 ° C, the temperature on the anchor can drop to -3.5 ° C and even lower, because. in calculations, the cross-sectional area of the aluminum bracket was assumed to be 1.8 cm 2 , whereas in reality it is 4-7 cm 2 . When using the stainless steel bracket, the temperature at the anchor was +8 °C. That is, when using aluminum brackets, the anchor works in the zone of alternating temperatures, where moisture condensation on the anchor is possible, followed by freezing. This will gradually destroy the material of the structural layer of the wall around the anchor and, accordingly, reduce its bearing capacity, which is especially important for walls made of material with low bearing capacity (foam concrete, hollow brick, etc.). At the same time, heat-insulating pads under the bracket, due to their small thickness (3-8 mm) and high (relative to the insulation) thermal conductivity, reduce heat losses by only 1-2%, i.e. practically do not break the "cold bridge" and have little effect on the temperature of the anchor.
3. Low thermal expansion of guides. Temperature deformation of aluminum alloy is 2.5 times greater than that of stainless steel. Stainless steel has a lower coefficient of thermal expansion (10 10 -6 °C -1) compared to aluminum (25 10 -6 °C -1). Accordingly, the elongation of 3-meter guides with a temperature difference from -15 ° C to +50 ° C will be 2 mm for steel and 5 mm for aluminum. Therefore, to compensate for the thermal expansion of the aluminum guide, a number of measures are necessary:
namely, the introduction of additional elements into the subsystem - movable slides (for U-shaped brackets) or oval holes with bushings for rivets - not rigid fixation (for L-shaped brackets).
This inevitably leads to the complexity and cost of the subsystem or incorrect installation (as it often happens that the installers do not use bushings or incorrectly fix the assembly with additional elements).
As a result of these measures, the weight load falls only on the bearing brackets (upper and lower), while the others serve only as a support, which means that the anchors are not loaded evenly and this must be taken into account when developing project documentation, which is often simply not done. In steel systems, the entire load is distributed evenly - all nodes are rigidly fixed - slight thermal expansions are compensated by the work of all elements in the stage of elastic deformation.
The design of the clamp allows you to make a gap between the plates in stainless steel systems from 4 mm, while in aluminum systems it is at least 7 mm, which, moreover, does not suit many customers and spoils the appearance of the building. In addition, the clamp must ensure free movement of the cladding plates by the amount of elongation of the guides, otherwise the plates will be destroyed (especially at the junction of the guides) or the clamp will unbend (both of which can lead to the falling of the cladding plates). In a steel system, there is no danger of unbending the clamp legs, which can occur over time in aluminum systems due to large thermal deformations.
Fire properties of stainless steel and aluminum
The melting point of stainless steel is 1800°C and aluminum 630/670°C (depending on the alloy). The temperature during a fire on the inner surface of the tile (according to the test results of the Regional Certification Center “OPYTNOE”) reaches 750 °C. Thus, when using aluminum structures, melting of the substructure and collapse of a part of the facade (in the area of the window opening) can occur, and at a temperature of 800-900 ° C, aluminum itself supports combustion. Stainless steel, on the other hand, does not melt in a fire, therefore it is most preferable for fire safety requirements. For example, in Moscow, when building high-rise buildings, aluminum substructures are not allowed to be used at all.
Corrosion properties
To date, the only reliable source on the corrosion resistance of a particular subfacing structure, and, accordingly, durability, is the expert opinion of ExpertCorr-MISiS.
The most durable are stainless steel structures. The service life of such systems is at least 40 years in an urban industrial atmosphere of medium aggressiveness, and at least 50 years in a conditionally clean atmosphere of low aggressiveness.
Aluminum alloys, due to the oxide film, have high corrosion resistance, but under conditions of high content of chlorides and sulfur in the atmosphere, rapid intergranular corrosion may occur, which leads to a significant decrease in the strength of structural elements and their destruction. Thus, the service life of an aluminum alloy structure in an urban industrial atmosphere of medium aggressiveness does not exceed 15 years. However, according to the requirements of Rosstroy, in the case of the use of aluminum alloys for the manufacture of elements of the substructure of the illegal armed formations, all elements must necessarily have an anodized coating. The presence of anodic coating increases the service life of the aluminum alloy substructure. But during the installation of the substructure, its various elements are connected with rivets, for which holes are drilled, which causes a violation of the anode coating in the fastening area, i.e., areas without anodizing are inevitably created. In addition, the steel core of the aluminum rivet, together with the aluminum medium of the element, forms a galvanic couple, which also leads to the development of active processes of intergranular corrosion in the places where the substructure elements are fastened. It should be noted that often the cheapness of one or another IAF system with an aluminum alloy substructure is due precisely to the lack of a protective anode coating on the system elements. Unscrupulous manufacturers of such substructures save on expensive electrochemical processes for anodizing products.
Insufficient corrosion resistance, in terms of durability of the structure, galvanized steel has. But after applying a polymer coating, the service life of a substructure made of galvanized steel with a polymer coating will be 30 years in an urban industrial atmosphere of medium aggressiveness, and 40 years in a conditionally clean atmosphere of low aggressiveness.
Comparing the above indicators of aluminum and steel substructures, we can conclude that steel substructures are significantly superior to aluminum ones in all respects.
Today, aluminum is used in almost all industries, from the production of food utensils to the creation of spacecraft fuselages. For certain production processes, only certain grades of aluminum are suitable, which have certain physical and chemical properties.
The main properties of the metal are high thermal conductivity, ductility and ductility, resistance to corrosion, low weight and low ohmic resistance. They are directly dependent on the percentage of impurities included in its composition, as well as on the technology of production or enrichment. In accordance with this, the main grades of aluminum are distinguished.
Types of aluminum
All metal grades are described and included in a single system of recognized national and international standards: European EN, American ASTM and international ISO. In our country, aluminum grades are defined by GOST 11069 and 4784. All documents are considered separately. At the same time, the metal itself is divided precisely into grades, and alloys do not have specifically defined marks.
In accordance with national and international standards, two types of unalloyed aluminum microstructure should be distinguished:
- high purity with a percentage of more than 99.95%;
- technical purity, containing about 1% impurities and additives.
Iron and silicon compounds are most often considered as impurities. In the international ISO standard for aluminum and its alloys, a separate series is allocated.
Aluminum grades
The technical type of the material is divided into certain grades, which are assigned to the relevant standards, for example, AD0 according to GOST 4784-97. At the same time, high-frequency metal is also included in the classification, so as not to create confusion. This specification contains the following grades:
- Primary (A5, A95, A7E).
- Technical (AD1, AD000, ADS).
- Deformable (AMg2, D1).
- Foundry (VAL10M, AK12pch).
- For steel deoxidation (AV86, AV97F).
In addition, there are also categories of ligatures - aluminum compounds that are used to create alloys from gold, silver, platinum and other precious metals.
Primary aluminum
Primary aluminum (grade A5) is a typical example of this group. It is obtained by enrichment of alumina. In nature, the metal in its pure form is not found due to its high chemical activity. Combining with other elements, it forms bauxites, nephelines and alunites. Subsequently, alumina is obtained from these ores, and pure aluminum is obtained from it using complex chemical and physical processes.
GOST 11069 establishes requirements for grades of primary aluminum, which should be marked by applying vertical and horizontal stripes with indelible paint of various colors. This material has found wide application in advanced industries, mainly where high technical characteristics are required from raw materials.
technical aluminum
Technical aluminum is called a material with a percentage of foreign impurities less than 1%. Very often it is also called unalloyed. Technical grades of aluminum according to GOST 4784-97 are characterized by very low strength, but high corrosion resistance. Due to the absence of alloying particles in the composition, a protective oxide film is quickly formed on the metal surface, which is stable.
Grades of technical aluminum are distinguished by good thermal and electrical conductivity. In their molecular lattice, there are practically no impurities that scatter the electron flow. Due to these properties, the material is actively used in instrument making, in the production of heating and heat exchange equipment, and lighting items.
Wrought aluminum
Wrought aluminum is a material that is subjected to hot and cold pressure processing: rolling, pressing, drawing and other types. As a result of plastic deformations, semi-finished products of various longitudinal sections are obtained from it: aluminum rod, sheet, tape, plate, profiles, and others.
The main grades of the deformable material used in domestic production are given in the regulatory documents: GOST 4784, OCT1 92014-90, OCT1 90048 and OCT1 90026. two or more solid states of matter.
The scope of wrought aluminum, as well as the one where an aluminum bar is used, is quite extensive. It is used both in areas requiring high technical characteristics from materials - in ship and aircraft construction, and on construction sites as an alloy for welding.
Cast aluminum
Cast aluminum grades are used for the production of shaped products. Their main feature is the combination of high specific strength and low density, which makes it possible to cast products of complex shapes without cracking.
According to their purpose, foundry grades are conditionally divided into groups:
- Highly hermetic materials (AL2, AL9, AL4M).
- Materials with high strength and heat resistance (AL 19, AL5, AL33).
- Substances with high anti-corrosion resistance.
Very often, the performance of cast aluminum products is improved by various types of heat treatment.
aluminum for deoxidation
The quality of manufactured products is also influenced by the physical properties of aluminum. And the use of low-grade grades of material is not limited to the creation of semi-finished products. Very often it is used to deoxidize steel - to remove oxygen from molten iron, which is dissolved in it and thereby increases the mechanical properties of the metal. To carry out this process, the most commonly used brands are AV86 and AV97F.