Aluminum can be joined by welding, brazing, soldering, adhesive bonding, riveting, stitching, or stapling and by means of a number of mechanical assemblies such as nuts and bolts, screws, and nails.
Metallurgy - Wikipedia
It can be given a wide variety of mechanical finishes by grinding, polishing, buffing, abrasive blasting, and burnishing. A variety of chemical finishes can be used, such as alkaline or acid etches, bright dips these give an extremely shiny finish to metal , chemical milling, and immersion plating. It is suited to an electrochemical process called anodizing. Or it can be electroplated with other metals or given organic coatings such as paint, lacquer, and plastic films.
Aluminum can be finished by porcelain enameling or metallizing. High-purity aluminum Annealing involves heating and then cooling slowly to make the metal less brittle. By alloying and proper thermal and mechanical treatment, however, it can be made much harder and stronger, with tensile strengths as high as megapascals.
Unlike some other metals, the strength and ductility of aluminum increase at very low temperatures. Upon melting, the solid metal expands about 7 percent in volume, the solidification shrinkage being 6. Hydrogen is the only gas known to be appreciably soluble in molten aluminum; its solubility increases with temperature but becomes nearly zero when the metal freezes. Aluminum may act as a base to form salts with acids or as a weak acid to form salts with strong alkalies.
It is stable in air because of a thin, transparent oxide film that forms on exposure to air, protecting the aluminum from further oxidation and reaction. Growth of this natural oxide film is self-limiting—that is, when a thin layer is formed, further growth is halted. Molten aluminum is protected in air by a thicker oxide coating, which also deters further oxidation.
Revert Alloys and Metals
Finely divided atomized or flake aluminum mixed with air and ignited will explode violently. Aluminum reacts rapidly with boiling water to liberate hydrogen and form aluminum hydroxide.
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In its superpure condition Superpure aluminum has many applications: in chemical equipment, in reflectors, as a catalyst in making gasoline, in fine jewelry, and in electronic components. Most aluminum used today, however, is alloyed with other elements to increase strength. The most common alloying elements are manganese Mn , magnesium Mg , copper Cu , zinc Zn , and silicon Si. Lithium [Li] is added to some of the newest alloys for the aerospace industry.
Smaller amounts of chromium Cr , zirconium Zr , vanadium V , titanium Ti , boron B , tin Sn , bismuth Bi , and lead Pb may be added for particular purposes. Iron is present as an impurity. Aluminum alloy products may be cast in a foundry into their final shape through sand-casting, permanent-mold-casting, or die-casting, or they may be cast into cylinders or rectangular blocks that are worked, or wrought, into products such as sheet, plate, forgings, or extrusions. The Aluminum Association of the United States has established systems for classifying foundry and wrought aluminum alloys.
Foundry alloys are identified by four-digit numbers, with the first numeral indicating the major alloying element or group of elements see table; sometimes a letter precedes the four digits to identify a variant of the original composition. Compositions of the major foundry alloys are listed in the table.
In addition to the major elements, foundry alloys may contain a small amount of titanium to refine the size of the crystallites or grains that make up the casting, as well as small amounts of manganese, chromium, or nickel for increased strength. The metallurgical structures and properties of the castings are also affected by the rate of cooling, which in turn is strongly affected by the casting method. The 3XX. X alloys are used in the highest volume.
Both copper and magnesium increase strength in the as-cast temper, and strength is increased by subsequent precipitation treatments at mildly elevated temperatures to produce fine intermetallic particles such as Mg 2 Si or Al 2 Cu. Even higher strength and ductility are obtained by a high-temperature solution treatment followed by rapid cooling and precipitation treatment.
When the silicon Si content exceeds 12 percent, silicon crystals in the castings enhance wear resistance as well. In the automotive industry , 3XX.
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X castings have replaced cast iron in transmission cases, intake manifolds, engine blocks, and cylinder heads because the reduced weight improves fuel economy. The 2XX. X alloys develop the highest strengths. Good design and foundry techniques must be followed to produce acceptable products, and heat treatment must be applied to develop high strength and to ensure high resistance to stress- and corrosion-induced cracking.
Because they have lower general corrosion resistance than other aluminum alloy castings, aluminum-copper castings are usually coated for critical applications. The 5XX. X alloy castings are specified when high resistance to corrosion in marine and other severe environments is demanded. These alloys are also used where the finish is of paramount importance and in the food-processing industry.
The 7XX. X alloys exhibit good finishing characteristics, are resistant to corrosion, and are capable of developing high strength by precipitation at room temperature. The 8XX. X alloys are used for sleeve bearings and bushings because the tin prevents seizing and galling. Typically, the primary ingredient is melted first, and the others are added to it. The traditional method used to prevent corrosion was to cover the metal with a surface coating, such as polymer.
This creates a barrier between the surface of the metal and the elements.
EonCoat is sprayed directly onto steel. Polymer relies on weaker mechanical bonds and merely sits on top of the metal. Once a polymer coating is scratched, moisture can get in and make contact with the metal. Once this happens, rusting is inevitable. What Is Alloying?
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Examples of Alloys In addition to increasing the strength of a metal, alloying may change other properties, including the resistance to heat, corrosion resistance , magnetic properties, or electrical conductivity. Steel is created from iron and carbon. Structures created from iron would eventually collapse. Stainless steel , an alloy made from iron and chromium, is more resistant to corrosion and staining when it comes in contact with water as opposed to iron and carbon steel.
Aluminum is soft and relatively weak.