Clad aluminum alloys

Aluminum cladding is an alloying process used to help prevent surface corrosion of other underlying metal components. This process involves hot rolling metal to produce a protective aluminum barrier. Clad aluminum alloys can be found in some heat exchanger tubing applications. 

An ideal model system was selected to study the interfacial factors with EIS [19]. The model system was Parylene C-coated Alclad (aluminum-clad aluminum alloy). In this system, the surface state of the top surface (salt solution/coating interface) and the adhesion of the coating (coating/metal interface) were modified to study the influence of these factors on the corrosion protection performance of the system. 

Table 10.2 Effect of Temperature Variation on Tensile Lap-Shear Strength of Hot-Melt Polysulfone Adhesive (UDEL P-1700) on 2024-T3 Clad Aluminum Alloy (0.05-0.076 mm) Glue Line) ...

H. W. Eickner, Weathering of adhesive bonded lap joints of clad aluminum alloys-Part I, Technical Report 54-447, Forest Products Lab. (1955). 

Brown, R. H. (ed.) 1969. Alclad and Clad Aluminum Alloy Products, Cambridge, MA MIT Press. 

Fig. 11.14 FCGR, da/dN, vs. KKj diagram for 7075-T6 clad aluminum alloy, as function of the / -ratio [8]...

II. Beryllium, zinc, clad and non-clad aluminum alloys, cadmium... 

Parker (1988) described durabilities of stressed and unstressed joints in clad aluminum alloy BS 2 L73 exposed to hot-wet, hot-dry, and temperate climates for up to 8 years. A variety of surface treatments were used. Joints were stressed to either 10 or 20% of their dry strength. 

Fig. 9. Microhardness profiles across interface of explosion-clad age-hardenable aluminum alloy 2014-T3 where the initial hardness is shown as Q (a) low,...

The resistance to corrosion of some alloy sheet is improved by cladding the sheet with a thin layer of aluminum or aluminum alloy that is anodic to the base alloy. These anodic layers are typically 5—10% of the sheet thickness. Under corrosive conditions, the cladding provides electrochemical protection to the core at cut edges, abrasions, and fastener holes by corroding preferentially. Aircraft skin sheet is an example of such a clad product. 

The aluminum alloys most commonly bonded are 2024 bare, 2024 clad and 7075 bare. Clad 7075 was also used extensively in early bonded structure but was largely abandoned after service performance demonstrated that it was susceptible to rapid dissolution or corrosion of the clad layer. Naturally aged tempers such as T3, in particular 2024-T3 because of its widespread use, are restricted to bonding with adhesives that cure at 250°F or below in order to avoid adversely affecting the temper. Various other alloys and tempers are bonded to a lesser extent, though the dominance of 7075 and 2024 is decreasing as higher-performance alloys and tempers are adopted. 

Clean metallic aluminum is extremely reactive. Even exposure to air at ordinary temperatures is sufficient to promote immediate oxidation. This reactivity is self-inhibiting, however, which determines the general corrosion behavior of aluminum and its alloys due to the formation of a thin, inert, adherent oxide film. In view of the great importance of the surface film, it can be thickened by anodizing in a bath of 15% sulfuric acid (H2SO4) solution or by cladding with a thin layer of an aluminum alloy containing 1 % zinc. 

It is important to note safety differences between the SRS reactors and LWRs. Since the SRS reactors are not for power production they operate at a maximum temperature of 90° C and about 200 psi pressure. Thus, there are no concerns with steam blowdown, turbine trip, or other scenarios related to the high temperature and pressure aspects of an LWR. On the of nd, uranium-aluminum alloy fuel clad with aluminum for the SRS reactors melts at a m ver... 

Clad Alloys. The heat-treatable alloys, in which copper or zinc are major alloying constituents, are less resistant to corrosive attack than a majority of the non-heat-treatable alloys. To increase the corrosion resistance of these alloys in sheet and plate form, they are often clad with a high-purity aluminum, a low-magnesium-silicon alloy, or an aluminum alloy containing 1% zinc. 

High-strength aluminum alloys are frequently deficient in resistance to corrosion. High-purity aluminum and certain aluminum alloys are considerably more resistant to corrosion but are deficient in strength. By applying surface layers of the corrosion-resistant metal to a core of the strong alloy a clad aluminum composite is achieved that has a corrosion unattainable by either constituent acting alone. 

Figure 28.2 shows the typical images of three Alclad panels (an aluminum alloy clad with nearly pure aluminum) tested with SO2 salt spray. The panels are (1) chromate conversion coated followed by priming with E-coat (2) chromate conversion coated followed by priming with Deft (chromated spray paint) and (3) plasma coated followed by priming with E-coat. The corroded area and corrosion width are also given in the figure. 

Alclad is an aluminum alloy clad with a nearly pure aluminum. The base alloy is AA 2024-T3, and the cladding has a specified composition of, in wt%, Cu 0.1, Si + Fe 0.7, Mg 0.05, Mn 0.05, Zn 0.1, Ti 0.03, others 0.3, and A1 the balance [9]. This Alclad is designated as 2A in this chapter, i.e., 2 representing 2024 T3 alloy and A representing Alclad. The pure aluminum has an excellent corrosion resistance. The clad is used to protect the base aluminum alloy from corrosion. 

Origins. Most of the radioactive waste at SRP originates in the two separations plants, although some waste is produced in the reactor areas, laboratories, and peripheral installations. The principal processes used in the separations plants have been the Purex and the HM processes, but others have been used to process a variety of fuel and target elements. The Purex process recovers and purifies uranium and plutonium from neutron-irradiated natural uranium. The HM process recovers enriched uranium from uranium—aluminum alloys used as fuel in SRP reactors. Other processes that have been used include recovery of and thorium (from neutron-irradiated thorium), recovery of Np and Pu, separation of higher actinide elements from irradiated plutonium, and recovery of enriched uranium from stainless-steel-clad fuel elements from power reactors. Each of these processes produces a characteristic waste. 

Zircaloy clad oxide fuel elements can be stored for decades in storage pools with very little risk of leakage. Metal fuels, especially those canned in magnesium or aluminum alloys, are less resistant and should not be stored as such in this manner for a prolonged time. The corrosion resistance of aluminum or magnesium clad fuel can be improved by electrolytic treatment yielding a protective oxide layer. 

Hundreds of thousands of freight containers have been built worldwide since the early 1960s. They are exposed to many types of climate and are heavily stressed by wear and tear. Freight containers consist of steel or aluminum alloy frames, clad with sidewalls and roofs made of steel, stainless steel, or aluminum alloys. The walls and roofs may be coil-coated. Container frames are usually blasted to grade 2 Vi of the Swedish Standard SIS 055900. 

Buses have a profiled steel framework that is clad on the sidewalls and roof with steel, galvanized steel, and aluminum alloys. The anticorrosive primer must therefore adhere well to all of these metals, and to glass-fiber-reinforced plastics. 

Bond failure can also occur if the surface is anodic relative to another joint component. An example would be clad aluminum adherends where a thin layer of pure aluminum overlays the base alloy. Such a surface layer is designed to be more corrosion resistant than the alloy, but to act as a sacrificial anode should corrosion occur. Although this approach works well for corrosion protection of the substrate material, it can be a disaster for bonded material if the adherend surface/interface corrodes. As a result, American companies tend to use unclad aluminum for bonding and provide other means of corrosion protection, such as painting [1,70]. On the other hand, European companies commonly use clad adherends, but with a thicker oxide (CAA) [6,18,71-73] that provides bondline corrosion protection. 

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