Alloying 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. 

The metal casting industry conventionally divides casting products into ferrous and nonferrous metals, in particular, iron-based, steel-based, aluminum-based, and copper-based castings. The other castings of low fractions include magnesium, lead, zinc, and their alloys. In the U.S., the foundry industry currently produces 11 million tons of metal product per year, with a shipment value of 19 billion. Of them, iron and steel accounted for 84% of metals cast.5 The remaining 15% of foundry operations are concerned with aluminum, copper, zinc, and lead production. Table 4.2 summarizes critical physical and thermal properties of aluminum, iron/steel, and cast iron. 

Aluminum antimonide, 3 53, 58 Aluminum arsenide, 3 270 Aluminum-base scrap, 75 349 Aluminum-beryllium alloys, 3 659 Aluminum beverage containers, 27 391-392... 

ALUMINUM BASE CHARGE INTERMEDIATE WIRE BRIDGE ALLOY CUP -------... 

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. 

Passivity of aluminum-based amorphous alloys and stainless steels and the catalytic activity of copper-based amorphous alloys... 

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. 

J. Wert, Microstructure of Friction Stir Weld Joints between an Aluminum-Base Metal Matrix Composite and a Monolithic Aluminum Alloy, Scr. Mater., Vol 49, 2003, p 607-612... 

---