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Aluminium Metallurgy

Since its first commercial production in 1854 aluminium has proved to be one of the most versatile and useful materials discovered and extracted from the earth.

It is the material of choice in a wide range of design and engineering applications because of its light weight, formability, corrosion resistance and high specific strength; and is the world’s second most used metal after iron (steels). Moreover, it is one of the most readily recyclable materials in use for packaging, medical and electrical applications, motor and automobile manufacturing. Nearly three-quarters of the aluminium ever produced in the world remains in use today because it is by its nature endlessly recyclable.

Given its inherent properties and potential as a sustainable resource, new ways of using aluminium in manufacturing processes and manufactured products are currently being investigated worldwide. Guidelines have been published by aluminium bodies in major aluminium producing countries such as Canada identifying the main challenges faced by the aluminium industry as:

  • The need for the development of new aluminium products having superior performance, produced using more efficient processes and
  • Better access to predictive and actual product performance testing facilities so as to meet the most demanding needs of the transportation, construction and energy industries.

For development of new products, various forms of casting, in particular, offer enormous possibilities since this production method is predominantly suited to the use of recycled aluminium. However, the casting processes need to be innovative and cost effective. This is an important area of research at AMRG.

Aluminium wrought alloys constitute about 80% of aluminium use worldwide for production of rolled plate, sheet, foil, extrusions, tube, rod, bar and wire. These are produced from cast ingots, mainly by direct chill (DC) casting, which requires a high degree of control over the solidification process. Complete control and prediction of the solidified structure of DC ingots have been investigated and reported by the American research centre, the SECAT program.

The main processing route of these alloys is by deformation but casting could be beneficial if appropriate casting route is selected. One of the processing routes tested at AMRG is near net shape casting of these alloys using rheo- and thixo-casting. For near or net-shape casting and forming of rheo and thixo-wrought alloys, however, there is almost no research reported in the open literature in spite of the potentials for significant cost savings and reduction in energy consumption. Difficulties associated with processing wrought alloys in a semi solid state are primarily due to their narrow solidification range.

Aluminium foundry alloys constitute almost 20% of Al-alloy consumption worldwide. Foundry alloys are used predominately in the transportation sector. Over the last two decades, casting has become more attractive as one of the most economical fabrication methods amongst the many metal forming processes available.

For aluminium foundry alloys, the most common casting techniques are sand and die casting. There are, however, certain drawbacks with casting including the formation of defects such as porosity, hot tears and segregation. As pointed out by Fleming [1,2] and Ghomashchi [3] such defects could be potential crack initiators during service operation. Therefore, considerable effort has been made to minimise such drawbacks, which has resulted in the introduction of more advanced casting processes, such as squeeze casting, Ghomashchi etal. [4] and rheocasting, Fan [5], Spencer and Fleming[6] and Ghomashchi’s group[7]. It is believed SSM processing of feedstock material could become the key remedy for minimising the drawbacks of the as-cast products, especially in pressure applied permanent mould castings.

The aluminum industry is vital to the Australian economy (nearly $10 billion worth of export in 2009), since not only is Australia a major source of raw material for aluminum production but is also an important primary aluminum producer ( view the sustainability report).

Australia is, in fact:

  • The world's largest producer of bauxite, producing 69.5 Mt in 2009
  • The largest producer and exporter of alumina, producing 20.2 Mt in 2009 with 16.3 Mt (81%) exported
  • One of the major aluminium producers in the world with aluminium production of 1.95 Mt in 2009. An estimated 0.27 Mt transformed into value-added downstream products and 1.67 Mt (86%) exported in 2009.

The Australian downstream processing sector continues to face strong market competition from imported products from Asian producers. In spite of strong domestic manufacturing, imports of aluminum products into Australia rose to164,000.00 tones in 2009 (95000 tons in 2000). In order to resist the progressive leakage of finished product manufacturing to emerging economies such as China and India, Australian manufacturers should be encouraged to invest in leading-edge design and manufacturing technologies rather than attempting to defend mature methods. Advanced modeling design techniques and fully-automated manufacturing, combined with a full awareness of the capabilities of aluminum will facilitate customer acceptance and even preference for aluminum. If such approach is coupled with less energy consumption and less pollutant production route, the benefit to the economic, social and environmental well being of the nation would be overwhelming.

As for SMG, aluminum research constitutes an important activity of the group. The main areas in aluminum metallurgy at SMG are as follows: (it is worth noting that amongst many Al-alloys, the foundry alloys of Al-Si with Mg or Cu are the focal point for SMG research)

  1. Solidification and foundry
  2. Heat treatment
  3. Welding and brazing
  4. Microstructure-properties relationships

For more information on specific projects, consult publication list or contact us.

References

  1. M.C., Flemings, Solidification Processing, McGraw-Hill, USA, 1974.
  2. M.C. Flemings, A. Mortensen, N.F., Dean, ‘Microsegregation in Cellular Solidification’, Metal. & Mats. Trans. A, 24A, p. 2295-2301, 1994.
  3. Ghomashchi, M.R. and Strafford, K.N., ‘Factors Influencing the Production of High Integrity Aluminum/Silicon Alloy Components by Die and Squeeze Casting Processes’, J. Mat. Process. Tech., Vol. 38, Nos. 1-2, P.303-326, 1993.
  4. R., Ghomashchi, and A., Vikhrov, ‘‘Squeeze Casting: An Overview’, J. Mat. Proc. Tech, Vol. 101, P. 1-9, 2000.
  5. Z. Fan, ‘Semisolid metal processing’, Inter. Mater. Rev., Vol.47, No.2, p. 49-85, 2002
  6. D.B. Spencer, R. Mehrabian, M.C. Flemings, ‘Rheological behaviour of Sn-15 Pct Pb in the crystallization range’, Metall. Trans., 3A, p.1925-1932, 1972
  7. O. Lashkari, S. Nafisi, and R. Ghomashchi, ‘Microstructural Characterization of Rheo-cast Billets Prepared by Variant Pouring Temperatures’, Materials Science and Engineering: A, 441, No. 1-2, P. 49-59, 2006
Structures and Materials Group (SMG)
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THE UNIVERSITY OF ADELAIDE
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