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Markets for high grades aluminum

Sometimes, major impurities of primary aluminum (Si, Fe, Cu, Ga...) are nocive to the use of the final products. It could be a reason of process (difficulties during rolling), or a matter of results by th use of the product (pollution of the substrate during operation by undesirable impurity, bad aspect of the surface...).

That’s why, high grades aluminum (beyond 99.9% i.e 3N) are used often because one single not wanted impurities.

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What are the main markets for 4N aluminum ?

• Bright finish plates
• Electrolytic capacitors
• Alloying components for other metals

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How do you manage to assure an interval for one given element ?

The easiest way is to have a very low content of residual element, and to make the addition in known quantities into the molten metal to reach the targeted content. But on the typical situation, the interval is assured by the mixing of different grades of high purity aluminums coming from different purification processes (like the Champagne).

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Why speaking about microstructure on very pure materials ?

Of course, purity of 5N materials is a major issue ; but these materials must meet several drastic criteria also on chemical homogeneity, grain size homogenity, cleanliness....

The purity is given mainly by the raw material which has been purified by the 3 layers process and by the segregation process.

But 5N material are often produced in alloys (mainly with Cu and Si) so to meet other physical properties like electrical conductivity, anti electro-migration within thin layers after deposition. Alloys ( < 4% other element) are not so simple to be homogeneous because the process is based on thermal principles so to make macro and micro segregation of alloying element in the matrix.

On the other hand, as the final product (i.e the sputtering target) must give an homogeneous layer on the substrate, grain size must be very fine. That’s why it is very important to give to the as cast material as much homogeneity as the chemical and grain size scale. PHP has developped the controlled grain process so to ensure this homogeneity by using the process.

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Is the Flat Panel Display market using Aluminum ?

Partially yes, but only for the LCD/TFT technology according to the design of screens manufacturers. Actually aluminum PVD targets are in competition with other elements because technical criteria are multiple.

We see that the 5N pure aluminum in shape of large rolled plates (1.1 m x 1.1 m) fine grain sized is requested because of its advantage during sputtering and its cost.

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Why do some products need high grade aluminum ?

Sometimes, major impurities of primary aluminum (Si, Fe, Cu, Ga...) are nocive to the use of the final products. It could be a reason of process (difficulties during rolling), or a matter of results by th use of the product (pollution of the substrate during operation by undesirable impurity, bad aspect of the surface...).

That’s why, high grades aluminum (beyond 99.9% i.e 3N) are used often because one single not wanted impurities.

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What are the main impurities in the 4N Al products ?

Two kinds of metallic elements must be distinguished when speaking global purity : the residual metallic impurities and the metallic dopants. The first one remain within the material after several steps of purification process at certain levels (depending on the nature of the element and on the process). Main residual impurities for 4N Al are : Si, Fe, Cu, Ga, Zn, B

The second ones are not to be considered as impurities, but as additive elements in order to maintain their content between a minimum and a maximum. This is sometimes requested by some applications involving either chemical etching or surface treatment or mechanical properties.

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How many processes are known and used for purification of pure aluminum ?

The oldest known process for purification is the melt zone refining. Its principle is based on the separation of element between the liquid and the solid metal during melting and solidification. A solid bar is placed in a mold in shape of long rod. An electromagnetic coil is moving very slowly along the mold so to make the aluminum melting just at its location on a few cm long. Due to their nature eutectic (Si, Fe,...) and peritectic elements (V, Ti,...) are moving within the liquid so to respect the rules of thermodynamics at the state of quasi equilibrium. The results is an purified part as regards eutectics behing the melt zone and an enriched part in front. With several passes, the first part of the rod is purified. The end of the rod must be cut and recycled to be purified again.

The other very known process if the electrolytic refining, called 3-layers refining. Purification is made using the selective electrical affinity of aluminum as regards a special mixture of melt salts. This process is known as the 3 layers because it uses A first layer of Al-30% Cu more dense than the layer of salts more dense than the refined aluminum.

The last process (more recent) is the segregation process. It uses the principle of fractionned crystallisation within a furnace filled with liquid aluminum. With an optimized tempature control, solid aluminum is generated on a cooled device and pressed like a sponge in the bottom of the furnace. The liquid aluminum is so enriched by eutectic elements. At the end of operation, liquid is poored so to extract a solid part of pure aluminum.

5N aluminum uses first the 3-layers refining and second the segregation process.

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What property is the most important for the 5N products ?

Among the main properties (see 6 features), the common one is the high purity level as regards metallic element. Every element is below 5 ppm, and the total is below 10 ppm.

Some of metallic elements contents are very low, below the detection limits of any laboratory device as the GDMS. For example : Ag, As...;

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Is there a preferred shape for 5N materials ?

As the main market for 5N materials is the semiconductor market (sputtering targets), 5N materials are mainly produced in ingots shapes (from 100 to 200 mm diameter). Ingots are cut in several lengths so to be forged and rolled into blanks.

But 5N products are also manufactured in shapes of rods, wires, rolled plates so to answer to requests of customers. PHP is able to developp special metallurgical products with the R&D Center

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Do I need a controlled microstructure for the 5N ingots ?

The patented controlled grain process gives to the grain size of each ingot a very fine grain and homogeneously distributed within the whole ingot. It suits very well to products which are forged or machined after, because this is a guarantee of homogeneity and consistency of the microstructure.

Top

How do you manage to assure an interval for one given element ?

The easiest way is to have a very low content of residual element, and to make the addition in known quantities into the molten metal to reach the targeted content. But on the typical situation, the interval is assured by the mixing of different grades of high purity aluminums coming from different purification processes (like the Champagne).

Top

Why speaking about microstructure on very pure materials ?

Of course, purity of 5N materials is a major issue ; but these materials must meet several drastic criteria also on chemical homogeneity, grain size homogenity, cleanliness....

The purity is given mainly by the raw material which has been purified by the 3 layers process and by the segregation process.

But 5N material are often produced in alloys (mainly with Cu and Si) so to meet other physical properties like electrical conductivity, anti electro-migration within thin layers after deposition. Alloys ( < 4% other element) are not so simple to be homogeneous because the process is based on thermal principles so to make macro and micro segregation of alloying element in the matrix.

On the other hand, as the final product (i.e the sputtering target) must give an homogeneous layer on the substrate, grain size must be very fine. That’s why it is very important to give to the as cast material as much homogeneity as the chemical and grain size scale. PHP has developped the controlled grain process so to ensure this homogeneity by using the process.

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What is the difference between cleanliness and purity ?

Purity is a property related to the chemical element content within the material ; the less of ppm the material has, the purer it is. Major impurities in aluminium matrix are Si, Fe, Cu, Ga, Ni as regards metallic elements.

The purity is estimated using the GDMS analytical method (Glow Discharge Mass Spectrometry) on a solid sample. Each Mendeleiev element is characterized at the sub ppm level (and for some like U, Th at the sub ppb level).

When speaking of purity, products are classified in 3N, 4N, 5N and 5N5 purities.

On the other hand, the cleanliness property is a concept related to physical particles which are introduced in the aluminum matrix during purification, casting and manufacturing. These particles can be alumina oxides, metallic particles, non metallic particles (carbon for example).

At last, cleanliness if often understood as the internal porosity and so as related to the gas content. It is known that gas (i.e hydrogen) is quite soluble within liquid aluminum during its elaboration. After casting, the over saturated gas can precipitate on any particle or grain boundary, so to give a “bubble”.

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Purity in 4N products

Two kinds of metallic elements must be distinguished when speaking global purity : the residual metallic impurities and the metallic dopants. The first one remain within the material after several steps of purification process at certain levels (depending on the nature of the element and on the process). Main residual impurities for 4N Al are : Si, Fe, Cu, Ga, Zn, B

The second ones are not to be considered as impurities, but as additive elements in order to maintain their content between a minimum and a maximum. This is sometimes requested by some applications involving either chemical etching or surface treatment or mechanical properties.

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