Vacuum Carbothermic Reduction of Alumina

The current industrial production of aluminum from alumina is based on the electrochemical Hall-Héroult process, which has the drawbacks of high-greenhouse gas emissions, reaching up to 0.70 kg CO2-equiv/kg Al, and large energy consumption, about 0.055 GJ/kg Al. An alternative process is the carbothermic reduction of alumina. Thermodynamic equilibrium calculations and experiments by induction furnace heating indicated that this reaction could be achieved under atmospheric pressure only above 2200° C. Lower required reaction temperatures can be achieved by alumina reduction under vacuum. This was experimentally demonstrated under simulated concentrated solar illumination and by induction furnace heating. By decreasing the CO partial pressure from 3.5 mbar to 0.2 mbar, the temperature required for almost complete reactant consumption could be decreased from 1800°C to 1550°C. Deposits condensed on the relatively cold reactor walls contained up to 71 wt% of Al. Almost pure aluminum was observed as Al drops, while a gray powder contained 60–80% Al and a yellow-orange powder contained only Al4C3, Al-oxycarbides and Al2O3.

Metallic Coatings for Brazing Aluminum Alloys

Because of their high specific strength and satisfactory corrosion resistance, aluminum alloys belong to the group of fundamental structural materials in modern engineering. Their wide use has been made possible as a result of developing advanced methods of processing and producing permanent joints by welding or brazing. However, the application of brazing aluminum alloys is limited because of the problems in removing the strong and chemically resistant oxide film. These problems can be overcome by using metallic coatings which themselves do not oxidize during heating in vacuum and, when deposited, the oxide film is broken up and can be removed from the surface of the parent material. The most promising method is to use metallic coatings in the form of individual components of the brazing alloy which forms in contact melting of the deposited coatings with aluminum in heating for brazing. This brazing method is referred to as contact-reactive brazing and is used widely for brazing aluminum alloys. This article provides an overview of the contact-reactive brazing process.

Surface Chemistry of Adhesion to Aluminum

Understanding the microstructure and chemistry of the aluminum surface is the key to designing coating and structural bonding systems that endure. The focus of this article is the examination of concepts common to all polymer/aluminum bonding applications and to discuss some common surface treatments alter the surface chemistry and microstructure and how these treatments affect adhesion. Topics covered in this review include: discussion of the untreated aluminum surface, adhesion to aluminum surfaces, prevention of hydration of the bonded interface, and pretreatments,

Plastic Flow of Aluminum in Explosive Welding

Joining of metals in explosive welding takes place as a result of their plastic deformation during a high speed collision and is usually accompanied by typical formation of waves at the interface. In welding aluminium, the weld boundary can also be straight if the speed of the contact point is νc is ≤ 1900 m/s. These welding conditions make it possible to prevent melting of the metal at the interface and increase at the same time its corrosion resistance. In this article, the effect of the dynamic collision angle on the special features of plastic flow of the metal in the vicinity of the contact boundary in welding sheets of AS5 aluminium is described.

Smelting of Aluminum

In this article, an overview of aluminum reduction from oxides and other aluminum compounds is provided. Specific topical coverage addressed are: physical chemistry of aluminum reduction, smelting processes including: the Hall-Héroult Process, the ALCAN Process, the Alcoa process, the Elliot-Mitt Process, and others. In addition, direct reduction of aluminum alloys, and electrodes for aluminum production are discussed.

Rolling of Aluminum

Because of its lightweight and strength, aluminum alloys are used are being used increasing for the production of lightweight construction. In addition to applications in the expanding transportation market, aluminum sheet and foil materials are traditionally used for food and medical packaging, thin foil, and fin stock for air conditioners and heat exchangers, decorative panels and lithographic sheet. Rolling is a process used for the production of strip or sheet. In this article, rolling processing of aluminum and aluminum alloys is discussed in detail and specific processes include: hot-rolling, cold-rolling, and rolling of aluminum foils.

Porosity Development and Modification in Al-Si Alloys: Effect of P and Sr

The benefits of Sr additions to Al–Si alloys to modify the eutectic are often impaired by the development of porosity, sometimes to the degree that benefits are negated. Experimental reports are reviewed in this paper, suggesting an explanation in terms of the oxide population in the melt. The unmodified silicon particles are nucleated by AlP, which has in turn nucleated on oxide bifilms. The oxide bifilms, which are essentially cracks, are straightened by the crystalline growth of Si particles, leading to increased crack size and consequently reduced mechanical properties. The addition of Sr improves properties by suppressing the formation of Si on bifilms and thereby preventing the straightening of the pre-existing cracks. Si is now forced to precipitate at a lower temperature as a coral-like eutectic. Unfortunately, the bifilms are now freed (the primary Si particles no longer exist to grow around and sequester the bifilms), remaining in suspension in the liquid metal, allowing them to act to block interdendritic flow and aid the initiation of the formation of pores, countering the benefits of the improved structure.

Pulsed TIG Welding of Aluminum

As a consequence of developments in the electronic control of welding power sources, there has been a trend for even inexpensive and widely used metal inert gas (MIG) and tungsten inert gas (TIG) welding machines to be equipped, as standard, with a high performance pulsed current waveform control function. Meanwhile advances in understanding of pulsed arc welding phenomena and the clarification of the associated functional effects have resulted in a gradual expansion of its scope of application and of improvements in practical performance. Thus inert gas shielded arc welding is entering an epoch when full scale pulsed arc welding will become standard. In this article, the progress of the development of pulsed TIG welding of aluminium is introduced, followed by a description of the main characteristics and finally examples of recent research concerning the improvement of weld quality are introduced.

Welding: Particulate and Gaseous Emissions

Fabrication and repair of aluminum components and structures commonly involves the use of electric arc welding. The interaction of the arc and the metal being welded generates ultraviolet radiation, metallic oxides, fumes, and gases. Aluminum is seldom used as the pure metal but is often alloyed with other metals to improve strength and other physical properties. Therefore, the exact composition of any emissions will depend on the welding process and the particular aluminum alloy being welded. To quantify such emissions, The Aluminum Association sponsored several studies to characterize arc welding emissions by the gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) processes for various combinations of base and filler alloys. In all cases, the tests were conducted under conditions that could be found in a production weld shop without forced ventilation. The concentrations of each analyte that a welder could be exposed to were greatly affected by the welding process, the composition of the base and filler alloys, the position of the welder, and the welding helmet. The results obtained can be used by employers to identify and control potential hazards associated with the welding of aluminum alloys and can provide the basis for hazard communication to employees involved in the welding of these alloys.