BS EN 2437:2002 – Chromate conversion coatings (yellow) for aluminium and aluminium alloys
1 Scope
This standard specifies yellow chromate conversion coating of aluminium and aluminium alloys.
It shall be applicable wherever referenced.
2 Purpose of process
To increase corrosion resistance and to improve the adhesion of paints and varnishes.
Type B coatings are also suitable for the repair of mechanically damaged anodic coatings.
3 Normative references
This European Standard incorporates by dated or undated reference provisions from other publications.
These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies.
ISO 8081 Aerospace process – Chemical conversion coating for aluminium alloys – General purpose
ISO 9227 Corrosion tests in artificial atmospheres – Salt spray tests
EN 2000 Aerospace series – Quality assurance – EN aerospace products – Approval of the quality system of manufacturers
EN 2334 Aerospace series – Acid chromate pickling of aluminium and aluminium alloys 1 )
EN 3997 Aerospace series – Aluminium alloy AL-P2024- – T3 – Sheet and strip – 0,4 mm a 6 mm 2)
4 Definitions
For the purposes of this standard, the following definition applies:
batch
parts treated at the same time in the same bath.
5 Classification
5.1 Thickness
– Type A: Mass per unit area from 0,2 g/m 2 to 0,42 g/m 2 for slight corrosion protection, where low electrical resistance is required ;
– Type B: Mass per unit area from ? 0,42 g/m 2 to 1 ,2 g/m 2 for good corrosion protection, with or without painting.
5.2 Materials
– Category 1 : Aluminium alloy with an Si-content ? 3,5 %;
– Category 2: Aluminium alloy with an Si-content ? 3,5 %.
6 Information for the processor
– Designation, see 1 6.
– Areas not to be chromated.
7 Condition of parts prior to processing
Soldering, welding, mechanical operations and heat treatments (except for cold storage) shall be completed.
The parts to be chromate coated after assembly (e.g. by spot welding) shall be pickled prior to assembly.
Areas not to be chromate coated shall be suitably masked.
8 Pre-treatment
8.1 Cleaning
The cleaning method shall be chosen according to the degree of contamination of the materials to be treated.
In general, the most effective method is degreasing with solvents followed by cleaning in an alkaline solution (see annex A, A.2).
8.2 Rinsing
The parts shall be rinsed thoroughly, e.g. by immersion followed by spray washing. It is recommended that a further rinsing be carried out in deionised water with a maximum specific conductivity of 1 00 ? S ? cm –1 .
8.3 Pickling
It shall not cause pitting or any alterations to the metallurgical characteristics or mechanical strength of the material.
The dimensions and the surfaces roughness value indicated on the drawings shall be observed.
Pickling is normally carried out in a solution containing chromate. Other methods may be used (see annex A, A.4).
BS EN 2437:2002 – Chromate conversion coatings (yellow) for aluminium and aluminium alloys