Industrial pure aluminium

Learn about the properties of industrial pure aluminum, commonly referred to as commercially pure aluminium. Understand the different degrees of purity and their relevance in different applications.

What is pure aluminium?

Usually metal purity is described by measuring the total content of impurity elements and subtructing  this number from 100%.

There is no generally adopted terms for the various degrees of purity in aluminium. This classification is the most common [1]:

• 99, 50-99,79 % Al – Industrial purity
• 99,80-99,949% Al – High purity
• 99,950-99,9959% Al – Super purity
• 99,9960-99,9990% Al – Extreme purity
• more 99,9990% Al – Ultra purity

Aluminium of high, super, extreme and ultra purities is of interest only to scientists and for very specific applications of aluminum. We will focus on the properties of industrial grade aluminum, on what is called commercially pure aluminium.

Industrial pure aluminium

Production

Aluminium of industrial purity is primary aluminium. Another name primary aluminum is “smelted aluminium”.

All primary aluminium production is based on the Hall-Heroult process [1]:

• Alumina refined from bauxite is dissolved in a cryolite bath with various fluoride salt additions.
• An electrical current is thn passed through the bath to electrolyze the dissolved alumina.
• Aluminium is collected as a metal pad at at the cathode.
• The separated metal is periodically removed by siphon or vacuum methods into crucibles.
• The crucibles are transferred to casting facilites where remelt or fabricating ingots are produced.

Figure 1 – Primary aluminium production [2]

Chemical composition of primary aluminium

 Impurities of primary aluminium

• The major impurities of smelted aluminium are silicon and iron.
• Zinc, gallium, titanium, and vanadium are also present as minor contaminants.

The designations of primary aluminium

International designation:

• Reference to grades of unalloyed aluminium is by purity alone (Figure 2).
• For example, 99,7% aluminium.

Aluminum Association designation:

• Standardized Pxxx have been estqablished (Figure 3)
• The digits following the letter P refer to maximum decimal percentages of silicon and iron, respectively.
• For example, P1020 is unalloyed smelter-pruduced aluminium containing no more than 0,10% Si and no more than 0,20% Fe.
• Common P grades range from P0202 to P1535.
• Each P grade incorporates additional impurity limits for control purposes.

 

Figure 2 – Chemical composition of casting unalloyed aluminium
with specified minimum aluminium content.
The fragment of EN 576 [3] 

Figure 3 – Chemical composition of casting unalloyed aluminium
without specified minimum aluminium content.
The fragment of EN 576 [3]

Chemical composition of industrial pure aluminium

Industrial unalloyed aluminium grades are divided into two categories:

• Casting composition: Al Alloy Group grade saccording to EN 1706 (Figure 4)
• Wrought comosition: Aluminium – 1000 series grades according to EN 573-3 (Figure 5)

Since pure aluminшum is unalloyed aluminшum, the term “grade” is often used instead of the term “alloy”.

Figure 4 – Chemical composition of unalloyed aluminium casting [4]

Figure 5 – Chemical composition of wrought unalloyed aluminium.
Fragment of EN 573-3 [5]

Applications

Casting products

Figure 6 – Casting methods and properties of casting unalloyed aluminium grades [4]

Wrought prodicts

Figure 7 – Applications and forms of products from wrought unalloyed aluminium grades [6]

Sources:

1. Properties of Pure Aluminium //Aluminum and Aluminum Alloys, AMS International, 1993.
2. Aluminium – A Light Metal. A Brief Introduction to Aluminium – TALAT Lecture 1100.01 / Toralf Cock, Skanaluminium, Oslo – 1999
3. EN 576:2004 Aluminium and aluminium alloys – Unalloyed aluminium ingots for remelting – Specifications
4. EN 1706:2020 Aluminium and aluminium alloys – Castings – Chemical composition and mechanical properties
5. EN 573-3:2019 Aluminium and aluminium alloys – Chemical composition and form of wrought products – Part 3: Chemical composition and form of products
6. EN 573-4:xxxx Aluminium and aluminium alloys – Chemical composition and form of wrought products – Part 4: Applications and product forms