Aluminum-based alloys

Quantitative aluminum deterrninations in aluminum and aluminum base alloys is rarely done. The aluminum content is generally inferred as the balance after determining alloying additions and tramp elements. When aluminum is present as an alloying component in alternative alloy systems it is commonly deterrnined by some form of spectroscopy (qv) spark source emission, x-ray fluorescence, plasma emission (both inductively coupled and d-c plasmas), or atomic absorption using a nitrous oxide acetylene flame. 

Precipitation-free zones at grain boundaries in an aluminum-base alloy. From D. A. Porter and K. E. Easterling, Phase Transformations in Metals and Alloys, 2nd ed. (London Chapman Hall, 1992), p. 306. 

Atmospheric Corrosion. The aluminum-based alloys in general are corrosion resistant to outdoor exposure with the exception of copper-bearing alloys. The Alclad alloys gave the best performance. The loss in tensile strength has been used as a measure of corrosivity and the loss of 1-2% of tensile strength over a period of 1 yr and in particular a loss of 17% was observed with 2017T alloy in 1 yr of outdoor exposure. 

The selection of an alloy for a specific application is based on the cost and the corrosion resistance of the alloy in the environment of interest. It is also possible to subject the chosen alloy to a process by which the corrosion resistance of the selected material can be improved within the acceptable limits. Some of the corrosion prevention and protection strategies with respect to the aluminum-based alloys are (i) design (ii) alloy selection and joint sealants (iii) aluminum thermal spraying anodic coatings (iv) inhibitors (v) conversion and organic coatings and (vi) cathodic protection. 

The aluminum-based alloys such as 1100, 3300, 5052, 6053, Alclad 3300, Alclad 1017-T and Alclad 20-24-T are highly resistant to most natural environments alloys of thickness <0.076 mm should not be used. Lead and bismuth added to alloys 2021 and 6262 improve chip breakage and other machining characteristics. 

A similar reaction occurs during pitting corrosion of iron and its alloys. Partial hydrolysis, leading to the formation of Al(OH) and Al(OH) may also occur, but all such reactions lead to the formation of acid, making the solution inside the pit much more aggressive than outside. Measurement of the pH inside a pit is not an easy matter, but estimates based on various calculations and on measurements in model pits lead to values as low as 1-2 for chromium-containing ferrous alloys and about 3.5 for aluminum-based alloys, depending on experimental conditions. 

Pitting corrosion is usually associated with active-passive-type alloys and occurs under conditions specific to each alloy and environment. This mode of localized attack is of major commercial significance since it can severely limit performance in circumstances where, otherwise, the corrosion rates are extremely low. Susceptible alloys include the stainless steels and related alloys, a wide series of alloys extending from iron-base to nickel-base, aluminum, and aluminum-base alloys, titanium alloys, and others of commercial importance but more limited in use. In all of these alloys, the polarization curves in most media show a rather sharp transition from active dissolution to a state of passivity characterized by low current density and, hence, low corrosion rate. As emphasized in Chapter 5, environments that maintain the corrosion potential in the passive potential range generally exhibit extremely low... 

Austenitic stainless steels are the most significant class of corrosion-resistant alloys for which intergranular corrosion can be a major problem in their satisfactory use. The problem is most often encountered as a result of welding but also may result from stress-relief annealing or incorrect heat treatments. Intergranular corrosion also can occur in ferritic stainless steels and in nickel- and aluminum-base alloys. 

Aluminum is consumed in forming the alanates. It was found that it doesn t matter where the aluminum comes from (i.e. sorption materials or container vessel walls). However, the use of alanates that are not aluminum deficient did not appear to degrade the strength of aluminum-based alloys when tested under long-term cycling conditions. 

The predominant method for the analysis of aluminum-base alloys is spark source emission spectroscopy. Solid metal samples are sparked directly, simultaneously eroding the metal surface, vaporizing the metal, and exciting the atomic vapor to emit light in proportion to the amount of material present. Standard spark emission analytical techniques are described in ASTM ElOl, E607, E1251 and E716 (36). A wide variety of well-characterized solid reference materials are available from major aluminum producers for instrument calibration. 

In 2001, Simon reviewed the theory of temperature-modulated DSC (TMDSC) with several examples of its applications, including many inorganic and coordination compounds [8]. Starink [9] provided a comprehensive review of the application of calorimetry in the analysis of a large variety of processes in aluminum-based alloys. 

Table IV. Plan of Experiment and the Chemical Composition (wt.%) of the Aluminum-Based Alloy Samples Studied...

The amount of impurities in the eutectic layers of the weld is one order higher than their mean content in the alloy for this reason, aluminum-based alloys of high purity are recommended to increase the joint strength. 

CAS 89-08-7 EINECS/ELINCS 201-881-6 Uses Electrolytic bath additive for production of hard anodic oxide coatings on aluminum and aluminum-based alloys colored coalings are abrasion resist, and attractive for architectural and other uses Features Colors depend on base metal composition, current dens., voltage, film thickness and electrolyte composition, particularly sulfate and aluminum contents Properties 49-51% act. 

Only in recent years have such universal analytical solutions been developed for XRF analysis. Even if there is still a large development potential for the future to be found in these programs, for example the precalibrated MetalQuant program for effective quantitative XRF analysis of different elements in iron, copper, nickel, cobalt and aluminum based alloys, most users already appreciate them. 

Rocher JP, Girot F, Quenisset JM, Pailler R, Naslain R, Precedes d elaboration des materiaux composites fiberux a matrice d alliage base aluminium, (Fabrication procedures of fibrous composites with aluminum based alloys), Memoires Sci Rev Metall, 69, Feb 1986. 

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