GOST 27637-88

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  ГОСТ 27637-88

GOST 27637−88 Semi-finished products of wrought aluminum alloys termouprochnennyh. Control of the microstructure on burnout by metallographic methods

GOST 27637−88

Group B59

STATE STANDARD OF THE USSR

SEMI-FINISHED PRODUCTS OF WROUGHT ALUMINUM
TERMOUPROCHNENNYH ALLOYS

Control of the microstructure on burnout by metallographic methods

Semi-finished products of wrought aluminium
thermo-hardened alloys. Control of microstructure for
presence of overburning by metallographic method

AXTU 1809

Valid from 01.07.89
to 01.07.99*
_______________________________
* Expiration removed by Protocol No. 7−95
The interstate Council for standardization,
Metrology and certification (I & C N 11, 1995). -
Note the manufacturer’s database.

INFORMATION DATA

1. PERFORMERS

G. Makarov, V. F. Nikolaev, V. I. Elagin, M. V. Samarina

2. APPROVED AND put INTO EFFECT by Decision of the USSR State Committee for standards from 23.03.88 N 676

3. INTRODUCED FOR THE FIRST TIME

4. REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

This standard specifies the metallographic method to control the microstructure on burnout after hardening of semi-finished products of wrought aluminum alloys termouprochnennyh.

A term used in the standard, and its definition is given in Appendix 1.

1. SAMPLING METHOD

1.1. Place of selection and the number of samples to control the microstructure shall conform to the requirements of normative-technical documentation on products.

In the presence of a natural temperature drop in the quenching units should be sampled from those parts of the semi-finished products, which when heated for hardening were in the areas of heating devices with the highest temperature, or from parts with the lowest values of electrical conductivity (pre-control eddy-current method).

1.1.1. For the manufacture of thin sections allowed to use the head samples subjected to tensile test.

1.1.2. When cutting samples on metal-cutting machines it is necessary to apply copious cooling technological mode to avoid heating of the samples.

1.2. Under the control of the microstructure of sheets, ribbon or wire, the thickness of the cone should correspond to the thickness or diameter of the semi-finished product. Under the control of a massive semi-length of the cone should be at least 15 mm, width — not less than 10 mm.

Of extruded products, the sample should be cut so that the area of the investigated sections along with the core was the area of coarse grain rim (if available).

1.3. The thin sections made and polished of technological regime, approved in a prescribed manner. Allowed sections of electropolishing after mechanical polishing.

1.4. Sections stored under conditions excluding oxidation, corrosion and mechanical damage, e.g. in desiccator with silica gel.

2. APPARATUS, MATERIALS, REAGENTS

Metallographic microscopes of various types, providing increase from 200 to 1000.

Beakers and flasks, glass, laboratory.

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

Desiccators according to GOST 25336−82.

Caliper according to GOST 166−80*.
______________
* Valid GOST 166−89. — Note the manufacturer’s database.

Silica gel technical GOST 3956−76.

Medical absorbent cotton wool GOST 5556−81.

Filter paper according to GOST 12026−76.

Nitric acid GOST 4461−77.

Hydrochloric acid by the GOST 3118−77.

Hydrofluoric acid according to GOST 10484−78.

Distilled water GOST 6709−72.

3. PREPARATION FOR CONTROL

3.1. The polished sections etched in a mixture of 5%-tion aqueous solutions of nitric, hydrochloric and hydrofluoric acids: 1.25 cmfertilizer 1.25 cmsalt, 2.5 cmhydrofluoric acid, 95 cmof water (1:1:2) or 2.5 cmof nitrogen, 1.5 cmsalt, 1.0 cmhydrofluoric acid, 95 cmof water (2,5:1,5:1

).

3.2. The etching solution is applied with a cotton swab and lightly wipe the surface of the last cone for more uniform etching. Allowed to etching by immersion in the solution.

Allowed to expose the etched portion of the socket to compare with it netravlenoy part where you revealed pores and dark inclusions of a phase of silicide of magnesium.

In the case of formation on the surface of the cone after etching, the dark heterogeneous plaque last is removed, slightly wiping the cone with a cotton swab dipped in 20% nitric acid solution.

3.3. The time of etching of a thin section from 5 to 30 s (depending on the brand of alloy, conditions of the polishing sections — mechanical, electrolytic) to clearly identify the boundaries of the intermetallic phases. Grain boundaries normally tempered material is not to be identified.

3.4. After etching, the sections are washed in running water, dried with filter paper.

4. CONTROL

4.1. Control of semi-burnout metallographic method is performed to identify the structural characteristics of burnout in the studied thin sections.

4.2. The microstructure of semi-finished products is controlled by the longitudinal or transverse etched thin section under magnification of at least 200. When conducting additional studies of the microstructure control on the longitudinal sections at the magnification of at least 500.

4.2.1. The microstructure of semi-finished products, manufactured with high degrees of deformation (for example, sheets, thin-walled profiles, pipes and wire), should be monitored when increasing from 400to 500.

4.3. Control five field sections in different zones of its surface, thus it is necessary to focus on stroke allocations of intermetallic phases.

5. EVALUATION OF THE RESULTS

5.1. Structural signs of burnout are common to all wrought aluminium alloys are divided into basic and related.

Examples of microstructures with signs of burnout are given in Appendix 2.

5.2. The main structural features of burnout:

the eutectic layer at the grain boundaries or subgrains and their joints (Fig.1−5), increasing in thickness and length depending on the magnitude of the exceeding of the melting temperature for this alloy when heated;

vnutricerepnae rounded education (globules) of the dispersed eutectic internal structure (Fig.1; 5) or eutectic edging of various thickness (depending on temperature) around excess melted particles of hardening phases propagating with increasing temperature for the entire amount of these particles (Fig.6).

5.3. Associated with burnout symptoms:

the porosity at the grain boundaries and in places of their joints;

individual recrystallized grains or groups of grains that are lighter than the matrix solid solution;

quenching cracks;

bubbles on the surface of semi-finished products.

5.4. The conclusion on the existence of burnout endure in identifying the main structural characteristics of burnout.

The presence of accompanying signs is not evidence of burnout.

5.5. The results of the control of microstructure on the burnout issue a Protocol stating:

grade alloy;

of a semi-finished product (size, batch number, etc.);

conclusion on the results of control;

date of inspection and names of performers;

designation of this standard.

ANNEX 1 (reference). THE TERM AND THE DEFINITION

ANNEX 1
Reference

Burnout — undesirable structural changes caused by high temperature heating of semi-finished for hardening above the solidus temperature of the alloy.

ANNEX 2 (mandatory)

ANNEX 2
Mandatory

Damn.1. Melting at the grain boundaries and their junctions, vnutricerepnae, global X250

Melting at the grain boundaries and their junctions, vnutricerepnae, global X250

Damn.1

Damn.2. Melting at the grain boundaries and their joints X500

Melting at the grain boundaries and their joints X500

Damn.2

Damn.3. Melting at the grain boundaries and their joints X250

Melting at the grain boundaries and their joints X250

Damn.3

Damn.4. Fusing the boundaries of subgrains X500

Fusing the boundaries of subgrains X500

Damn.4

Damn.5. Vnutrismennyh, global, reflow the joints of the grains X500

Vnutrismennyh, global, reflow the joints of the grains X500

Damn.5

Damn.6. X500

X500

Damn.6

Intermetallic phases:

and partially melted, with piping; b — naplavlenie