Sorting by alloys “at a glance”?

A very important type of aluminum scrap sorting – alloy sorting. Usually aluminum scrap comes from the collection points to the plant for sorting of scrap metal scrap as part of other non-ferrous metals and their alloys. Here is a typical picture of the manual sorting of several ducts of the individual components of scrap by their appearance, origin and typical application.

The most popular – and expensive – categories of aluminum scrap are “electrical aluminum” and “food grade aluminum.”. These aluminum scrap category are considered to be the cleanest and are commonly used in the smelting charge to dilute the excessive content of an alloying element, for example, magnesium or silicon, and iron, in the preparation of a melt for casting aluminum ingots-pillars of secondary alloys 6060 or 6063. These ingots go for aluminum profile extrusion.

However, As will be shown below, the aluminum scrap categories can be very patchy and uncertain in their chemical composition. Therefore, using this scrap without preliminary instrumental control of its chemical composition is very risky: you can spoil the entire aluminum melt in the furnace.

The steady growth of the primary aluminum prices, as well as increasingly stringent environmental requirements for the production of aluminum, making it increasingly important to increase the efficiency of recycling aluminum scrap in a new high-grade aluminum. The problem lies not only in the maximum extraction of aluminum, but also effectively reusing alloying elements, which are already present in the aluminum scrap.

Aluminum: primary and secondary

Aluminum is the second after the steel in terms of world production and consumption. The attractiveness of aluminum as the material for the manufacture of various products and structures give it unique properties, such as the:

• light weight,
• sufficiently high strength properties,
• good corrosion resistance,
• processability by all methods of cold and hot forming,
• high electrical and thermal conductivity;
• high reflective properties.

Natural raw material for extraction of primary aluminum minerals are minerals bauxite. For the production of primary aluminum requires a large amount of electric energy.

The secondary aluminum is called the aluminum, which is made from aluminum scrap and waste. While consuming only 5 % energy and, respectively, released only 5 % greenhouse gas compared to the production of primary aluminum. Recently secondary aluminum (secondary aluminum) is often called more “tolerant”: “recycled aluminum” (recycling aluminum).

Grades and alloys of aluminum

Aluminum is used mainly in the form of grades of aluminum and aluminum alloys:

• Aluminum grades are unalloyed aluminum with an aluminum content of at least 99,00 %, and with the specified limits of impurities and contaminants.
• aluminum alloys have the limits of the content of impurities and contaminants also, and the predetermined intervals containing one or more alloying elements. These alloying elements provide aluminum alloys special properties as compared with unalloyed aluminum, as well as other aluminum alloys.

Aluminum alloys are divided into two large groups – wrought alloys and casting alloys:

• from wrought alloys, the final aluminum products are produced by the methods of metal processing by pressure: rolling, pressing, forging, stamping, etc.. P.
• from casting alloys, products are produced by various casting methods (in sand molds, under pressure, chill and so on. P.).

Alloying elements of aluminum alloys

Most wrought alloys, at least, on 90 % percent, and most of them – to 95 %, It consists of aluminum. The remaining percentages take alloying elements, impurity and pollution. The exceptions are some 4xxx series alloys.

Casting alloys differ greater content of alloying elements, as well as impurities and contaminants. So, in some aluminum alloys, the alloying elements exceed 20 % [1].

By major alloying elements all alloys – and wrought, and foundries – divided into series. for instance, Wrought alloys are classified into eight such series with the corresponding main alloying elements:

• 1xxx – brand unalloyed aluminum
• 2xxx – Copper, and magnesium
• 3xxx – manganese
• 4xxx – silicon
• 5xxx – magnesium,
• 6xxx – magnesium and silicon
• 7xxx – Zinc, and copper
• 8xxx – iron, as well as other elements.

The main alloying elements and impurities most popular in the aluminum industry wrought aluminum alloys are shown in Table 1. Blue color indicates characteristics of these alloys for compatibility with other alloys, or their differences from other alloys.

Figure 1 – Popular wrought aluminum alloys

Categories and aluminum scrap Group

The European standard EN 13920 determines 15 categories of aluminum scrap: from pure unalloyed aluminum to aluminum slag. American classification system divides the aluminum scrap in the 44 categories (cm. more here).

In practice, the collection points for aluminum scrap usually use only about a dozen different groups of aluminum [3], such as:

• wires
• food
• profiles
• cables (without insulation)
• mixed
• radiators
• shavings
• boats
• cans.

Scrap of unalloyed aluminum

This category generally involves aluminum scrap sheets, tape, pipe and, sometimes, profiles. In appearance and strength are easily confused with similar sheets, ribbons, pipes and radiators, aluminum-manganese alloys 3xxx series, which contain up to 1,5 % manganese. The level of strength of these alloys somewhere on 20 % higher, than the grades of unalloyed aluminum.

Note, that the erroneous application of the 3xxx series alloys instead of aluminum, not alloyed grades, for example, for the preparation of alloys 6060 и 6063 lead to an excessive content of manganese in the melt, which is an undesirable impurity in them a limit of up to 0,10 %.

Scrap of aluminum profiles

Among aluminum extrusions can occur several alloys of different batches, which may not be compatible, for example, with the most popular alloys for profiles – alloys 6060 и 6063:

• 2014 и 2024. Copper content up to 5,0 %, manganese – up 1,2 %. Not suitable for the preparation of alloys 6060 и 6063: too much copper and manganese. Used in aircraft. Very hard pressed, therefore have a simple cross-sectional shape with thick walls.
• 5xxx series alloys. Magnesium content up to 4,0 % and manganese – up 1,0 %. The increased manganese content limits the use for the preparation of, for example, alloys 6060 и 6063. The higher content of magnesium, the harder pressed. Have a simple cross-sectional shape.
• 6060 и 6063. Manganese content, copper, chromium and zinc, not more than 0,1 %. They may have complicated cross-sectional shape, including, with several cavities and thin walls. Massively used for the manufacture of frames of windows and doors, as well as facade constructions.
• 6061. Iron content up to 0,7 % and copper – to 0,40 %. The content of silicon and magnesium in 1,5-2 times higher, than the alloys 6060 и 6063. pressing difficulty – medium, Profiles are simple cross-sections.
• 6082. Manganese content up to 1,0 % It restricts the use of alloys 6060 и 6063. Profiles are simple cross-sections.
• 7005yu Profiles from this alloy were previously used for the manufacture of enclosing structures, for example, stained glass. Until recently, the alloy 1915 included in the Standard 22233 as a material for walling. It contains up 5,0 % zinc.

Alloy sorting of aluminum scrap

Currently, for sorting metals and their alloys in the “field” conditions, that is, directly on the storage of aluminum scrap, two methods of analyzing the chemical composition of aluminum alloys are used:

• X-ray fluorescence spectrometry (XRF)
• laser-spark emission spectrometry (LIBS).

Portable X-ray fluorescence spectrometers are used for the identification and analysis of metals for nearly 40 years. Over the years, these hand-held spectrometers have gone from a heavy appliance, that it was necessary to carry on the back, precision instrument to the size of a small drill. Portable laser spectrometers appeared relatively recently – in the past 10 years. Optical Emission Spectrometers (OES) are somewhat larger, than x-ray and laser spectrometers. Therefore, they are more convenient to use in the lab, and not in the field warehouse of scrap metal or foundry Stockyard.

What gives sorting of aluminum scrap with identification of alloys:

• preventing undesirable contaminants and alloying elements from being loaded into the melt;
• introducing the required alloying elements into the melt in specified quantities;
• separation of high and low value alloys;
• preparation of alloys of specified narrow ranges of chemical composition;
• identification within the series aluminum alloys with increasing scrap value of a single alloy.

Sources:

1. Aluminum and Aluminum Alloys (ASM Specialty Handbook) – 1993
2. Advancements in Handheld XRF Technology Improve Scrap Sorting and Segregation /J. Margalit – 20^th Intern. Recycling Aluminium Conference, 2012, Salzburg, Austria.