EN 4707-2020 pdf download.Aerospace series-Acid pickling of aluminium and aluminium alloys without hexavalent chromium.
• or solvent;
• or vapour solvent.
NOTE If necessary (laminated parts/oxidized parts), carry out a chemical deoxidizing (with rinsings) or abrasive blasting after pre-degreasing.
2) A second alkaline degreasing shall be performed after pre-degreasing, if necessary.
The alkaline degreasing shall be:
• corrosion inhibited;
• preferably silicate free and borate free type (especially for dye penetrant inspection).
Generally alkaline solutions with pH between 9 (nine) and 11 are considered as degreasing-etching solutions, whereas those with pH between 7 (seven) and 9 (nine), are considered only as degreasing solutions.
For the parts to be bonded, a silicated free alkaline solution is mandatory.
3) After alkaline degreasing/cleaning, the parts shall be thoroughly water rinsed and inspected for water break. Cleaning shall be repeated iIbreak occurs.
7.2.3 Treatment
Immediately after pre-treatments, the parts shall be pickled in one of the solutions specified below.
To ensure a well pickled surface, excessive bath loading and shielding of parts by each other shall be avoided:
Type of substances that can be used in pickling:
• Type A: Nitric or sulfonitric;
• Type B: Phosphosulfonitric;
• Type C: Sulfonitro-ferric Iluoride free:
• Type D: Sulfonitro-ferric with fluoride.
Table A.1 specifies pickling bath to be used depending on the application.
7.2.4 RinsIng
After each treatment bath, water rinsing is mandatory. This operation has to be composed by at least one
recycled rinsing. Recycled rinsing is generally completed by non-recycled or low-flow rate rinsing.
Several quality of rinsing water can be used for rinsing but the water used before surface treatment (see
Table 1) shall have a conductivity not more than 20 i.iS/cm.
Rinsing shall be carried out consecutively to the pickling step in running water with a temperature not
exceeding 40 °C.
7.2.5 Drying
The parts shall be dried except for those submitted for subsequent chemical treatment, anodizing or desmutting/ chemical conversion.
The temperature shall not exceed 80 °C.
After drying. parts shall be protected against contamination.
In case of bonding and paint applications, parts shall be stored under clean, dry conditions.
8 Required characteristics and Inspection
8.1 Parts
8.1.1 Inspection before treatment
By visual inspection, make sure that the parts to be protected/treated are free from defects such as:
scratches, corrosion pits, cracks, etc. prejudicial to the appearance or the effectiveness of the protection. Adherent chips and metal particles must be removed beforehand using a clean cloth.
8.1.2 Cleanliness
During the degreasing phases, each final rinsing operation must be followed by a water break test in order to evaluate the wettability (and the cleanliness) of the surfaces.
This test consists of covering the parts with a uniform water film. This water film must cover the parts for at least 30 s at ambient temperature without any discontinuity in the film. Otherwise, degreasing phases have to be repeated.
This test is optional for automatic lines.
8.1.3 Inspection after treatment
When subjected to visual Inspection, the pickled surfaces shall be of a homogeneous appearance and free from pitting, stains and contamination.
8.2 Process
8.2.1 Air used for drying or other operations shall be substantially dry and free from oil.
8.2.2 Chemical analysis of the pickling solutions (and of the different baths involved in the sequence of operations) shall be carried out at regular intervals to determine the content of active products, heavy metal (e.g. iron, copper), chloride, etc., when requested.
8.2.3 The bath shall be discarded when pitting of parts occurs or when solid material starts to precipitate on cooling the solution to ambient temperature. The process must be managed by monitoring the significant parameters as aluminium and contaminant contents.
8.2.4 The purity of the rinsing water shall be determined by conductivity/resistivity measurements.
8.2.5 When required for adhesive bonding, the test to the relevant bonding standard shall be carried out to ensure that the process has been correctly applied.
8.2.6 Each pickling process must be characterized by Its specific etching rate range. All pickling process must not lead to localized attack.
8.2.7 The etching rate of the complete sequence of operations must be periodically measured to ensure the control of the process.EN 4707-2020 pdf download.