Aluminium Casting Alloys - Report Example

Aluminium casting alloys Name Course Tutor Date Executive summary Today aluminium is the major non-ferrous metal that is used widely. This metal is utilized in the construction industry, the packaging industry, transport sector, electrical engineering and mechanical engineering and design. New areas of use are continuously emerging as the benefits of this substance increasing. Aluminium alloys are non-ferrous metal which has aluminium (Al) as the major metal. The usual alloying elements in aluminium are copper, manganese, magnesium, silicon and zinc. There exist two major categorizations, consisting of wrought alloys and casting alloys, where both are then subdivided into the heat-treatable and non-heat-treatable. Nearly 85 percent of aluminium is utilized for wrought products, for instance foils, rolled plate and extrusions. Table of Contents Executive summary 2 Table of Contents 3 1.0 Introduction 4 2.0 Aluminium production 4 3.0 Aluminium casting alloys 5 4.0 Fabrication 9 5.0 Recycling of aluminium 12 6.0 Shaping by casting 12 7.0 Conclusion 13 8.0 References 14 1.0 Introduction Aluminium in its pure form is a malleable, silvery element of belonging to boron group (Kaufman, 2000, P.116). This element has a symbol Al and atomic number 13. Research suggests Aluminium as the most plentiful metal on the crust of the earth but very reactive to naturally establish in element form. It is though establish in over more than 275 different minerals, the major source found to be bauxite ore, which has 52% Al203, 27.5% Fe203 and 20.55 of H20 (Campbell, 2008). Aluminum alloys are categorized into three groups including wrought heat treatable alloys, wrought non-heat-treatable alloys and casting alloys. However, this report will only focus on what is aluminium casting alloys, its production, its fabrication and its recycling. 2.0 Aluminium production Kaufman (2000, p.116) state that the bauxite mining is regarded as the first stage of aluminium production. In this stage, alumina which is a raw material is mined and processed. Processing of aluminium oxide (alumina) must be done by electrolysis in order to convert it to aluminium. Degarmo, Paul, Black & Kohser (2003) claim that this process is realized by the application of the Bayer chemical procedure in the alumina processing plant. The aluminium oxide is discharged from the various materials in bauxite in the solution of caustic soda, which is sorted out to get rid of all insoluble elements. The aluminium hydroxide is thus precipitated from this a caustic soda solution, cleaned and dried whilst the caustic soda solution is then recycled. Calcinations is then carried out which give aluminium oxide (Al2O3) as the end-product, which as fine particles white powder (Kaufman, 2000, p.117). Primary aluminium is manufactured in smelters. In this stage alumina is processed to extract pure aluminium. The alumina reduction into liquid form is carried out at nearly 950c in the fluorinated bath under higher powerful electrical current (Campbell, 2008). The process occurs in electrolytic cells in which carbon cathodes makes the bottom pot forms the negative electrode. Positive electrodes (Anode) are maintained as the top pot and are used in the process at the time it reacts with the oxygen arising from alumina (Kaufman, 2000, p.117). 3.0 Aluminium casting alloys Campbell (2008) claims that Aluminium casting alloy is a production process where the liquid aluminium is poured into other elements containing a hollow cavity with a defined desired and given time to solidify. The solidified piece is referred to as casting. Aluminium casting alloys consist of both heat treatable and non-heat-treatable alloys. Shankar (2000) argues that the main forms comprises of 2xx.x series (Al-Cu), 3xx.x series (Al-Si + Mg or Cu), 4xx.x series (Al-Si), 5xx.x series (Al-Mg), 7xx.x series (Al-Zn) and 8xx.x series (Al-Sn). The 2xx.x; 3xx.x; 7xx.x, and 8xx.x alloys could be made stronger by precipitation hardening; however the properties that are established are not as high as for those of wrought heat treatable alloys (Check figure 1). Figure 1: aluminium and alloying elements Source: (Esabna, 2013) According to Esabn (2013) the alloys of aluminum-copper ((Cu) 2xxx) alloys generally contain up to 10 percent copper. The copper offers a considerable boost in strength and allows for hardening of precipitation. The alloying of copper into aluminum also reduces corrosion resistance and ductility. The most common use of alloys in the 2xxx series are aerospace, rocket fins and military vehicles. The alloying of manganese ((Mn) 3xxx) into aluminum adds strength fairly by means of strengthening the solution and enhances stress hardening whilst not noticeably corrosion resistance or decreasing ductility (Esabna, 2013). These are fair strength non heat-treatable components which maintain strength at raised temperatures and are rarely applied for key structural applications. The alloying of silicon and aluminum decrease melting temperature and enhances fluidity. Silicon in aluminum forms a non heat-treatable alloy; but, in alloying it with magnesium it forms an alloy of precipitation of hardening heat-treatable. As a result, both heat-treatable and non heat-treatable alloys are found in the 4xxx series (Degarmo, Paul, Black & Kohser, 2003). The alloy of magnesium and aluminum adds strength via solid solution hardening and enhances their stress hardening capability. These alloys make the biggest strength non heat-treatable aluminum alloys, therefore are applied widely for structural use. Alloy falling in 5xxx series is manufactured majorly as plate and sheet and only irregularly as extrusions Degarmo, Paul, Black, & Kohser, 2003). On the other hand, alloying of silicon and magnesium to aluminum forms the magnesium-silicide (Mg2Si) compound (Esabna 2013). The production of this compound offers 6xxx series the heat-treatability. The alloys in the 6xxx series are simple and cheaply extruded and therefore are most frequently established in a wide range of extruded shapes. These alloys produce a significant corresponding system with that of alloy belonging to 5xxx series (Shankar, 2000). The alloying zinc and aluminum with other elements, mainly magnesium and copper forms alloy of heat-treatable aluminum with the highest strength. Cast aluminium alloys produce cost-effective products owing to their low melting point, though they normally possess lower tensile strengths compared to wrought alloys. The most significant cast aluminium alloy arrangement is Al–Si, in which the highest degree of silicon (4.0–13%) contributes to offer good casting attributes (Degarmo, Paul, Black & Kohser, 2003). Aluminium alloys are extensively utilized in engineering components and structures where corrosion resistance or light weight is needed. Alloys consisting majorly of aluminium have been critical in aerospace making ever since the launch of aircraft which is metal skinned. Alloys of Aluminium-magnesium are lighter compared to aluminium alloys and less flammable compared to alloys containing a higher degree of magnesium. Aluminium alloy float ups will maintain their clear shine in a dry setting owing to the formation of a plain, protective coat of aluminium oxide (Kaufman, 2000, p.117). In a wet situation, galvanic corrosion may happen when aluminium alloy is put in electrical contact with another metal having negative corrosion prospective compared with aluminium. The Aluminum Association registered compositions of Aluminium alloy. Different organizations publish more particular standards for the producer of aluminium alloy, as well as the Automotive Engineers standards society, particularly subgroups of aerospace standards and ASTM International (Kaufman, 2000, p.116). Aluminium alloy casting can be as provided in the cycle below. Figure 2: casting alloys process Source: (Campbell, 2008) 4.0 Fabrication Aluminum casting alloys are mostly annealed to make them soft and enhance ductility (Campbell, 2008). Annealing, a practice that decrease hardness and strength whilst adding ductility, could also be applied for both the heat treatable and non-heat-treatable grades of wrought. Annealing process is applied at the time of complex cold forming process to enable further forming with no danger risk of cracking the sheet. The most ductile and formable state for aluminum casting alloys is manufactured by complete annealing to the O state (Campbell, 2008). If cold-made aluminum casting alloys are heated to adequately high temperatures for adequately longer time, annealing will take place in three phases: recovery, recrystallization and grain development. At the time of recovery, the internal strains owing to cold work are decreased, with the loss of its strength and a recovery of its ductility. At the period recrystallization, new unstressed nuclei is created and grow up to the time they interrupt on one another to produce a fresh recrystallized particle structure. Heating for a long period of time or at high temperatures will typically lead to grain development, which is usually undesirable (Wallace, 2006). Nevertheless precipitation hardening, aluminium casting alloys is heated to a higher enough temperatures to take a considerable level of alloying elements into solid form (Fig. 3). Figure 3: Fabrication process Source: (Kaufman, 2000) It is thus fast cooled to room the temperature, locking the coating elements in the solution. On heating again to a moderate temperature, the metal that host it rebuffs an alloying element in form of strong fine precipitate just numerous angstroms in the diameter (1 Å = 10-9 m) (Kaufman, 2000). The precipitate makes matrix stress in the lattice which acts as obstacles to the movement of dislocations and offers opposition to slip, thus boosting its strength and solidity (Fig. 4). Figure 4: solidification Source: (Kaufman, 2000) Precipitation hardening comprises of three stages; solution heat treating, rapidly quenching to a lower temperature and aging. In solution heating process, aluminium alloy is reheated to the temperature which is adequately higher to place the alloying elements in the solution (Kaufman, 2000). After maintaining the solution treating heat for a long time for diffusion of atoms into this solvent matrix to take place, it is cooled to a reduce the temperature to a room temperature so as to maintain the alloying elements held in the solution. At the time of aging, alloying elements held in the solution precipitate to produce a consistent distribution of fine particles. Shankar (2000) argues that the decline in strength of aluminum alloy at high temperatures is dependant on composition. If the level the elements present, particularly Copper, Nickel, and Manganese are low down, the strength is significantly lowered at temperatures of 250°C however if the maximum acceptable levels of these elements are present, the alloy retains moderate strength at this particular temperature (Kaufman, 2000). It must be taken into consideration that other issues could restrict the usage of castings at high temperatures. 5.0 Recycling of aluminium Previously before the word “recycling” became trendy, recycling circuits had existed in the aluminium industry (Shankar, 2000). Utilized parts manufactured from aluminium alloys including aluminium residue emerging from manufacture are far too expensive to wind up as land-fill. One of the key advantages of this non-ferrous metal is its use in construction industry, since its parts are used in re-melting. Sanders (2001, p.23) postulates that this experience gathered in several decades, the application of modern technology in scrap process, remelting and cleaning exhaust gas including our regular efforts to create new, environmentally-based manufacturing technology makes us capable of achieving the best potential and effective rate of recycling. Similarly, they also assist in making the most resourceful application of energy and secondary materials. 6.0 Shaping by casting Casting of aluminium alloys stand in the shortest path from raw materials to finished products–a reality that has been recognized for more than five thousand years (Ravi, 2005). Through constant development and, partly, by a careful return to classic techniques like the lost-form method, casting of aluminium alloys continues to be at the front position of technical growth. The best advantage of the process of casting is that the potential of shaping the element are practically unlimited. Castings are therefore, cheaper and easier to manufacture compared to joined or machined components (Ravi, 2005). The typical waiving of succeeding machining not only the outcomes in a better density and force lines route but also in a high degree of strength. 7.0 Conclusion Aluminum alloys are very useful than aluminum itself, since they give good strength to the material, by fixing dislocations while maintaining other properties of aluminium. It is however recommended that correct recognition of the aluminum type be made and appropriate procedures be followed so as to confirm performance of the alloys before it can be used. This is because more than 200 casting alloys and 400 wrought alloys exist and are registered by Aluminum Association today. 8.0 References Esabna. (2013). How and why alloying elements are added to aluminum. Viewed on 7th September 2013. http://www.esabna.com/us/en/education/knowledge/qa/How-and-why- alloying-elements-are-added-to-aluminum.cfm Campbell, F. (2008). Elements of Metallurgy and Engineering Alloys. ASM International, Degarmo, E., Paul., Black, J T & Kohser, RA. (2003). Materials and Processes in Manufacturing (9th ed.), Lodon: Wiley. Kaufman, J. (2000). Introduction to aluminum alloys and tempers. New York: ASM International. Ravi, B. (2005). Metal Casting: Computer-Aided Design and Analysis, (1st ed.). London: PHI. Shankar, A. (2000). Study of the Interface Reaction Mechanism Between Molten Aluminum and Ferrous Die Materials. Ph.D. Worcester Polytechnic Institute. Sanders. R. (2001). Technology Innovation in aluminium Products. The Journal of The Minerals, 53(2), p. 21–25. Wallace, J. 2006. A Guide to Correcting Soldering. London: North American Die Casting Association. Read More