GOST 9.904-82

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  ГОСТ 9.904-82

GOST 9.904−82 unified system of corrosion protection and ageing (ESSEX). Aluminum-based alloys. The method of accelerated testing of dissecting corrosion

GOST 9.904−82

Group Т99

STATE STANDARD OF THE USSR

Unified system of protection against corrosion and aging

ALUMINUM ALLOYS

The method of accelerated testing of dissecting corrosion

Unified system of corrosion and ageing protection.
Alluminium alloys. Accelerated test method for exfoliating corrosion

Date of introduction 1983−07−01

Promulgated by the decree of the USSR State Committee on standards of 26 July 1982 N 2858

REPLACE GOST 9.018−74

REISSUE


This standard specifies a method for accelerated testing of dissecting corrosion (hereinafter RAC*) aluminum alloys (the alloys) without protective coating.
______________
* RSK is a special type of subsurface corrosion, growing mainly in the direction of maximum strain vector and is accompanied by the formation of cracks and delamination of the individual metal particles.

1. SAMPLE REQUIREMENTS

1.1. For testing of semi-finished products and parts used flat samples with a size of 60x40 mm.

The thickness of the sample is determined according to claim 1.3.

Allowed to use samples of other shapes and sizes, the surface area (excluding the area of face sides) must be at least 48 cm.

Side of the sample with the largest size are arranged in the direction of maximum deformation parallel to the surface of the semi-finished product or part.

1.2. A plating layer on the samples removed in accordance with GOST 9.021−74.

1.3. The end face along the perimeter of the sample is subjected to mechanical processing. One surface sample less than 5 mm thick are subjected to mechanical or chemical treatment 20% thickness and 5 mm — machined to 50%.

Surface roughness parameter RA of the processed surface should be not more than 2.5 µm according to GOST 2789−73, a rough surface is to meet the requirements of standards or technical specifications for semi-finished product or part.

Allowed to test samples less than 3 mm thick without treatment.

1.3.1. Before chemical treatment the samples are degreased in an organic solvent (e.g. benzene, acetone), and then etched in a solution containing 100 to 200 g/DMsodium hydroxide at a temperature from 333 to 363 K (60 to 90 °C) to achieve the desired thickness. After that, samples were washed under running water, decolorized in a solution containing 300 g/lof nitric acid for 6 min, again washed in running, and then in distilled water and dried in air.

1.4. For testing of welded joints of semi-finished products or parts with thickness less than 10 mm is used flat samples with dimensions of not less than 25Х80 mm.

Welded seam in the middle of the specimen perpendicular to the long side.

When testing welded joints of thickness 10 mm and width of the sample should be at least 40 mm, and the length is determined from the heat affected zone so that the distance from the end of the sample to this area was at least 30 mm.

Sample thickness should match the thickness of the semi-finished product or part.

1.4.1. Mechanical treatment is subjected to only the mechanical side of the perimeter of the sample.

The roughness parameter of processed and unprocessed surface must comply with the requirements of section 1.3.

1.5. The number of samples shall be at least five for each option. Under option understand the samples with identical parameters.

1.6. From each option before a final rating store no less than three control samples.

Control samples are stored under conditions precluding the development of corrosion, for example, in a desiccator with desiccant (silica gel etc.).

2. APPARATUS, MATERIALS AND REAGENTS

The profilometer according to GOST 19300−86.

Caliper according to GOST 166−89.

Desiccator, according to GOST 25336−82.

Containers of different sizes, made of inert materials (e.g. glass, vinyl plastic).

Beakers and flasks laboratory glass according to GOST 25336−82.

Silica gel technical GOST 3956−76.

Medical absorbent cotton wool GOST 5556−81.

Rectified ethyl alcohol according to GOST 5962−67.

Varnish AK-20.

The aviation gasoline according to GOST 1012−72.

Acetone according to GOST 2768−84.

Distilled water GOST 6709−72.

Sodium hydroxide according to GOST 4328−77.

Nitric acid GOST 4461−77.

Orthophosphoric acid according to GOST 6552−80.

Chromium (VI) oxide according to GOST 3776−78.

Hydrochloric acid by the GOST 3118−77.

Potassium dichromate according to GOST 4220−75.

Sodium chloride according to GOST 4233−77.

Potassium nitrate according to GOST 4217−77.

3. PREPARING FOR THE TEST

3.1. On one surface of the sample in the corner labeling indicating the number of variant and sequence number of the sample. Markings contribute to the test Protocol.

Place marking to protect the paint coating, such as varnish brand AK-20.

3.2. The sample was subjected to etching in a solution containing from 50 to 100 g/DMsodium hydroxide at temperature from 323 To 333 K (from 50 to 60 °C). The etching time from 30 to 60 s.

3.3. Before the test samples wiped with a cotton swab soaked in ethanol.

4. TESTING

4.1. The tests are carried out in tanks of various capacity in full immersion of the samples into solution for testing.

4.2. Samples in solution have a vertical.

4.3. Not allowed to test in the same container samples of alloys of different systems.

4.4. The solution for the test and the test duration is selected depending on the composition of the alloy and its heat treatment in accordance with table.1.

Table 1

Notes:

1. Solution 3 is used instead of the solution 2 in that case, if the corrosion products do not make it difficult to estimate the RSC.

2. In solution 2 may be replaced with potassium dichromate in a mixture of: chromium (VI) oxide — 9 g/DMpotassium dichromate and 1.5 g/DM.

3. For research trials is allowed to increase the duration of test in solutions 1 and 4 to 14 days, 2 and 3 to 4 days.

4.5. The solutions were prepared in distilled water.

4.6. The solution volume is 10 cmby 1 cmsample surface, the solution temperature from 291 to 298 K (from 18 to 25 °C).

4.7. At the end of the test, the samples washed in running, and then in distilled water and dried in air.

4.8. If the corrosion products on the surface of the sample after the test does not allow to assess the degree of development of the RAC, the corrosion products are removed in one of the solutions:

nitric acid — 300 g/DMwithin 10−20 min, the solution temperature from 291 to 298 K (from 18 to 25 °C);

a mixture of orthophosphoric acid, 52 g/land chromium (VI) oxide 20 g/DMfor 10−30 min, the solution temperature from 368 to 371 K (95 to 98 °C).

4.9. Inspection of the samples is carried out not later than 6 hours after completion of the test.

5. EVALUATION OF THE RESULTS

5.1. Evaluation criteria of resistance of the alloy at the RSC are:

the nature of the change in appearance of the sample;

the area of delamination on each surface of the sample, %;

the total length of the ends cracked, %.

5.2. In assessing the changes in appearance of the sample set color change, the presence of ulcers, delaminations, and determine their sizes.

5.3. The total length of the ends are cracked () for each sample in percent is calculated by the formula

,

where  — the length of the end section affected by cracks, mm;

 — the perimeter of the specimen, mm.

Example of calculation of the total length of the ends with cracks is given in Appendix 1.

5.4. The area of delamination on each surface of the sample is determined visually or using methods of quantitative metallography and expressed as a percentage of the square of the estimated surfaces for each sample.

5.5. The resistance of the alloy at the RSC estimate for each of the sample points on a scale, are given in table.2.

Table 2

5.6. If the area with the delamination on the surface corresponds to the points (for points 3, 4 or 5), and the diameter of individual delaminations — the higher the score, the sample estimate of a score (i.e. 4, 5 or 6).

If the area with the delamination on the surface corresponds to the points (6, 7 or 8), and the diameter of individual delaminations of less than 5 mm, the sample estimate of a score (i.e. 5, 6 or 7).

5.7. 9 and 10 scores include the samples affected by cracks across the cross section (thickness). Samples that have only superficial cracks are referred to 8 points.

5.8. The final scoring is carried out by the highest score obtained in the evaluation of the two surfaces or ends.

5.9. Specific examples of the RAC on a scale given in Annex 2.

5.10. The variant carried out at the average value of the points determined with accuracy up to 0,1, according to the formula

,

where is the number of samples in the embodiment.

5.11. If necessary, additional evaluation is carried out metallographic examination to determine corrosion depth.

5.12. The results of the test to enter in the minutes, which indicate:

brand and chemical composition of the alloy;

view of the semi-finished product or part;

the technology of manufacturing of semi-finished product or part;

heat treatment;

surface condition;

the size of the sample;

the number of the solution for testing;

the duration of the test;

criteria for evaluating the resistance of the alloy at the RSC;

score.

ANNEX 1 (recommended). EXAMPLE OF CALCULATION OF THE TOTAL LENGTH OF THE ENDS CRACKED

ANNEX 1
Recommended

ANNEX 2 (informative). TYPICAL EXAMPLES OF DISSECTING CORROSION

ANNEX 2
Reference

Score 8

A score of 9

Score 10