Unalloyed aluminium grades

Terms and definitions

Unalloyed aluminium grades

• Unalloyed aluminum have aluminium content of not less than 99,00%, rest – impurities.
• Impurity is a metallic or non-metallic element presented in the metal, which is not controlled by the minimum content.
• Refined aluminum is unalloyed high-purity aluminium (aluminium content is not less 99,950%), which is produced as a result of special metallurgical treatments.

Primary aluminum is unalloyed aluminum:

• which is made of alumina, usually by electrolysis, и
• which has an aluminum content of at least 99,70%.

Unalloyed aluminum subdivided into grades depending on the content of impurities.

Aluminium alloys

Aluminium alloy is aluminum:

• which contains alloying elements,
• wherein the aluminium content is higher, than any other element, and
• in which, aluminium content of not more 99,00%

Alloying element is a metallic or non-metallic element, which is:

• controlled at a predetermined interval content, to provide the specific properties of the alloy.
• intentionally added to the melt of aluminium.

Every aluminum alloy has its own designation, for example, alloy 2017. This alloy designation clearly identifies its chemical composition, including, Intervals content of alloying elements and tolerances of the maximum content of impurities. It should be noted, that sometimes, including, the standards, used the expression “alloy brand”. However, the difference between the meaning of the expressions “alloy brand” и “alloy” it is not clear.

Aluminium grades classification

Among the grades of aluminum, they are distinguished by the method of smelting and the purpose:

• primary aluminium
• wrought aluminium
• casting aluminium

Primary aluminium grades

Primary aluminum is classified into:

• aluminum of extra high purity (aluminum content is higher 99,995%)
• high purity aluminum (aluminum content from 99,95 to 99,995%)
• aluminum of technical purity (aluminum content from 99,00 to 99,85%)

Wrought unalloyed aluminium grades

Wrought unalloyed aluminium have a purity of 99,00 to 99,85%. They are intended for manufacturing products by hot and cold metal forming, i.e rolling, extrusion, drawing, stamping, etc.

Casting unalloyed aluminium grades

Casting unalloyed aluminum have very limited application, mainly for the production of cast rotors of electric motors. They have a purity of 99,00 to 99,70 %.

Primary aluminium

Two methods of designation

The  grades of unalloyed aluminum can be designated in two ways:

• the minimum content of pure aluminum, for example, Al 99,70 % or
• on the maximum content of silicon and iron – a Phhhh.

The letter P followed by the numbers, that indicate the maximum content of silicon and iron, eg:

• R1020 – is unalloyed primary aluminum – primary aluminum stamp, not more than 0,10% silicon and not more than 0,20% gland.
• R0506 – The brand of primary aluminum, not more than 0,05% silicon and not more than 0,06% gland.

These two different approaches to estimate the properties of primary aluminum reflected in:

• European Standard EN 576. This standard specifies requirements for chemical composition of different grades of primary aluminum in accordance with the international approach. The provisions of EN 576 broadly in line with the provisions of the same international standard ISO 115:2003 (Table 2).
• American approach (Table 3).

 Table 3 

Table 4

Unalloyed auminium grades at LME

• Standard primary aluminium, which is the subject of international trade, including, on the London Metal Exchange (LME) is a grade of unalloyed aluminum with a purity 99,70% [3].
• This is equivalent to American brand P1020 Primary Aluminum.
• This provides the maximum grade aluminum content of iron in the metal 0,20% and the maximum content of silicon 0,10% (hence, P1020).

The metal with a low aluminum content, for example, 99,50%, is considered to be the products of lower quality and are usually sold at a discount. The metal may be melted and mixed in a foundry with a high-grade metal, to get ingots, that meet the requirements of LME or finished casting products. The main impurities in the preparation of a high-grade metal are iron and silicon. Increasing the aluminum content above 99,70% It means essentially proportional reduction of iron and silicon content, while the content of other impurities remains practically unchanged [3].

Wrought unalloyed aluminium

Aluminium grades in EN 573-3

Table 5 – The grades of wrought unalloyed aluminium according to EN 573-3
Applications of wrought unalloyed aluminium

Refined aluminium

Refined aluminum with a purity aluminum call from 99,99 % to 99,9999 %. Abroad, the purity of such aluminum is often denoted “4N to 6N” – by the number of nines (Nother). This was prepared by special methods of primary aluminum. Refined aluminum grades are used in the following areas:

• Foil for electrolytic capacitors (1199 grade
• semiconductor Manufacturing
• Plates for the manufacture of flat panel displays
• Pin layout in the electronics industry
• Production of thin films
• Production of high purity and high purity alumina powders
• Electronic drives (memory disks)
• For products with a smooth surface and jewelry
• Production of ultrapure aluminum alloy for aerospace

Techical pure aluminium

• Electrical conductors: wire, twisted prvodniki, bus, transformer strips (grades 1350)
• Lithographic plates (mark 1100)
• Packing: aluminum foil grade (grade 1100, 1145, 1050, 1235)
• Extruded tubes for food, chemical and brewing industry (brands 1050, 1060)
• Heat exchangers (brands 1050, 1070, 1145)
• Passive seismic protection systems. Low yield stress and high ductility are used to effectively dissipate seismic energy during earthquakes (grade 1050A)
• Aluminum bottles (grades 1050A and 1070A)

Casting unalloyed aluminium

• According to International aluminium classification, the grades of casting unalloyed aluminium are 1xx series of casting alloys.
• Although often referred to as alloys, there is no reason to attribute them to full alloys: they contain at least 99,00 % aluminum and have not formally alloying elements,
• Unlike primary aluminum grades, they control the ratio of iron and silicon content.

Rotor Casting

• Most cast aluminium motor rotors are produced in specialized compositions by smaller vertical die casting machines. The objective is consistent electrical performance.
• Alloys 100.0, 150.0, and 170.0 (99.0, 99.5, and 99.7%Al, respectively) specify impurity limits and ratios for the formation of intermetallics least harmful to castability.
• Titanium and vanadium are precipitated or complexed by boron additions. Iron and silicon contents are controlled.
• These impurity controls improve and minimize variations in conductivity and reducereduce the tendency for microshrinkage and cracking during solidification [4].

Because unalloyed aluminum can be purchased at lower cost than rotor alloys, there has been a trend for their substitution in rotor production. For example, P1020 unalloyed smelter ingot has
the same purity as 170.2 but without impurity ratio controls and with uncontrolled titanium and vanadium content. Ignoring these differences results in variable electrical performance and poor castings.

Figure 1 – A cast aluminium motor rotor

Aluminium for deoxidation of steel

Aluminum is used for steel deoxidation, as well as the production of ferroalloys and powders for aluminothermy. This aluminum is produced both from virgin raw materials, and from scrap and aluminum waste. Produced ingots and pellets. For these aluminum grades characterized by a very high content of impurities – in a total amount up to 13 %.

The sources:

1. Properties of Pure Aluminum / A. Sverdlin //Handbook of Aluminium: Vol.1 Physical metallurgy and Processes, ed. G.E. Davis, D.S. MacKenzie, 2003
2. Aluminum and Aluminum Alloys / ed. J.R. Davis – ASM International, 1993
3. The Aluminium Industry /James F King – Woodhead Publishing, 2001
4. Aluminum Alloy Castings Properties, Processes, and Applications / J. Gilbert Kaufman, Elwin L. Rooy – 2004 ASM International
5. Aluminium Alloy Castings. Properties, Processes and Applications / J.G. Kaufman, E.L. Rooy – ASM International, 2004