Socomore Socosurf Surface Treatment Process

Aluminium alloys make up at least 20% of new aircraft such as A350 and B787, and almost 70% of legacy aircraft such as A320 or B737. To make sure aluminium components are fit to face the rigours of flight, various surface treatments need to be applied.

Within the European Union and United Kingdom, REACH has restricted various historic products and processes, as they are deemed unsafe for operators and the environment. Safer chemicals are gradually replacing substances such as borate, hydrogen fluoride (or fluoric acid) and hexavalent chrome (sometimes referred to as Chrome VI, Cr(VI) or chromate), and leading to changes in the processes and products used.

In keeping with this shift in technology, Socomore have developed a range of aluminium surface treatments that meet the requirements of major OEMs as well as the restrictions put on the industry by the European Commission and other parties.

There are three main phases in the aluminium surface treatment process.

Cleaning and Degreasing

The initial step of alkaline degreasing is used to clean the part and remove oil, dirt, grease and ink from the surface.

Sococlean A3432 is a notably safe cleaner. Free from borate, silicate, hexavalent chrome and VOCs, it proves an environmentally friendlier and more secure choice. This product offers versatility, as it may be used to degrease aluminium, titanium or stainless steel alloys. Applicable through immersion or spraying, its properties can be maintained by additive top ups. The ink remover additive Sococlean IR can also boost its degreasing abilities even further.

Deoxidising or Desmutting

Once the part is clean, the metal needs to be prepared for treatment. This can be done either by deoxidising the part, or through a sodic etching and desmutting process. These processes remove a thin layer of aluminium oxide from the surface.

Socosurf A1858 and Socosurf A1806 are fluoride- and hexavalent chrome free products suitable for deoxidising, desmutting and etching aluminium prior to treatment. A1858 is the acid concentrated part for setting up the bath while A1806 is the part essential to give all its characteristics to the treatment bath.

The properties of the batch can be adjusted by the addition of additives including Socomul TA and Socosurf A1850.

Treatment – Conversion or Anodisation

Different treatments can be applied to the metal depending on the desired properties of the part. Two of the more popular processes used in aerospace are chemical conversion and anodisation. Both of these processes improve the corrosion resistance properties and paint adhesion of the metal, while chemical conversion can also improve electrical conductivity.

Socosurf TCS and Socosurf PACS are trivalent chrome and zirconium based chemicals, and therefore safer to use than the now restricted hexavalent chrome. TCS is used to convert the metal, creating a protective layer on the surface while PACS is used to enrich the layer. TCS and PACS can be used both for chemical conversion or as post anodization sealing. Additional additives are available to assist in these processes.