IS 12573: Method for Macro Etch Test for Wrought Aluminium and Aluminium Alloy Products

2010·0.79 MB·English

by  Bureau of Indian Standards

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IS 12573 (2010): Method for Macro Etch Test for Wrought
Aluminium and Aluminium Alloy Products [MTD 22:
Metallography and Heat Treatment]
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IS 12573 : 2010
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Indian Standard
METHOD FOR MACRO ETCH TEST FOR WROUGHT
ALUMINIUM AND ALUMINIUM ALLOY PRODUCTS
( First Revision )
ICS 77.120.10
© BIS 2010
B U R E A U O F I N D I A N S T A N D A R D S
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002
February 2010 Price Group 2
Metallography and Heat Treatment Sectional Committee, MTD 22
FOREWORD
This Indian Standard (First Revision) was adopted by the Bureau of Indian Standards, after the draft finalized
by the Metallography and Heat Treatment Sectional Committee had been approved by the Metallurgical
Engineering Division Council.
This standard was first published in 1988. The revision has been taken up in order to update the standard
in the light of experience gained in its usage and to align it with the latest practices being followed in this
field in the country.
In this revision following modifications have been done:
a) Scope has been modified;
b) Clauses on selection of sample and sampling plan have been modified; and
c) Clause on specimen preparation has been modified.
Macro etch test method is frequently used as an evaluating technique for revealing solidification structure
segregation, general distribution and size of inclusions, porosity, grain size, flow lines surface condition,
manufacturing defects and method of manufacture. It is done by etching a suitably prepared specimen and
examining it visually or at low magnification (not exceeding ten diametres). Macro etch test method provides
inspections of large area as opposed to micro etch test method.
IS 12573 : 2010
Indian Standard
METHOD FOR MACRO ETCH TEST FOR WROUGHT
ALUMINIUM AND ALUMINIUM ALLOY PRODUCTS
( First Revision )
1 SCOPE 2.3.1 Cast Billets
Discs should be cut from the ends covering entire
1.1 This standard describes the method for carrying
cross-section of billet.
out macro etch testing of aluminum and aluminum
alloys and some of the widely accepted etching 2.3.2 Extrusions
solutions currently in use. The products covered by
Discs should be cut from the ends of the extruded
this standard are cast billets, extruded, rolled and
section covering the full cross-section.
drawn products, such as, bars, profiles, sheets, wires,
etc, and forgings 2.3.3 Forgings
1.2 The macro etching technique reveals defects on
Discs should be cut transverse to the long dimension
the surface etched by specific chemical and can be
to reveal defects, such as, cracks, bursts, piping, etc.
classified as described in IS 15264 : 2002
For revealing flow lines, forging, should be cut
‘Geometrical product specification (GPS)—Surface
parallel to the long dimension. In complicated
imperfections—Terms, definitions and parameters’.
forging, cutting should be done after careful study
of the anticipated flow line.
2 SELECTION OF SAMPLE
2.3.4 Sheets and Plates
2.1 Defects which are revealed in macro etch testing
For observing surface defects, a reasonably large
may be introduced at various stages of
sample should be taken. Samples may be cut in small
manufacturing. To avoid wasteful work on defective
pieces for convenience of handling. For observing
material, sampling ought to be done at an early stage
laminations, transverse section has to be prepared.
of manufacture. However, the sample should not be
taken so early that further working can introduce 2.3.5 Tubes
serious defects. If the part is to be sectioned,
Suitable drawn tube samples to be made for
selection of the cutting plane is determined by
checking defects along and across the drawing
directionality or fibering due to the working process,
direction.
by the suspected or known form of defects, and by
the general form or nature of the part, namely,
3 SPECIMEN PREPARATION
casting, forging, extrusion, etc.
2.2 While stages of examination shall depend on 3.1 Specimen shall be extracted by sawing or any
agreement between the manufacturer and the other mechanical means suitable for the stock to be
purchaser, it is commonly done at semi-finished and examined. However, care should be taken to prevent
finished stage and shall include the following: mechanical deformation/cold working during
cutting and to provide sufficient coolant to restrict
a) Stages of manufacture at which inspection
any structural change due to heating during cutting.
needs to be carried out;
3.2 Machined surfaces mostly serve the purpose for
b) Definition of batch and batch size;
macro etching. However, machining with blunt tool
c) Location and number of specimens per batch
or at unfavourable speed and feed can distort the
to be examined;
surface and give misrepresentation of the grain
d) Degree of surface preparation for macro structure. The usual procedure is to take roughing cut
etching; and finish cut. This shall provide smooth surface
finish reasonably free from cold work. A shaper or
e) Etching solution and method; and
milling machine should be preferred to a lathe,
f) Permissible quantum of defects preferably
which provides control of cutting speed on a flat
portrayed photographically or schematically.
surface’.

2.3 A few common methods of sampling wrought 3.3 Degree of surface finish to be obtained on the
aluminium and aluminum alloys are given as below. specimen surface (to be examined) shall depend on
1
IS 12573 : 2010
the purpose of etching and on the severity of the Details of macro etchant and the method used are
etchant. Most macro etch are aggressive enough to furnished in Table 1.
bring out some details of macro structure on a rough
cut surface but the over-etching often obscures 4 VIEWING AID
important details In general, a smoother or highly
Etched specimen shall be examined visually or at
polished surface requires less etching to bring out
low magnifications. The optimum viewing
the same amount of gross details and reduces the
conditions for etched surface are when the light is
possibility of losing fine details.
oblique to the angle of viewing. Generally, high
3.4 For revealing fine details, a very smooth surface
intensity light source is not required but a low power
finish is required. Specimen surface should be ground
independent light source is essential.
by emery paper up to ‘0’ grade to obtain a smooth
surface finish with suitable lubricant to avoid cold 5 INTERPRETATION OF RESULTS
working or heating.
Indications that may be commonly seen after macro
3.5 After surface preparation, the specimen shall be
etching are given below:
cleaned with suitable solvent to eliminate the
possibility of producing uneven attack by the macro a) Centre Defect—Pipe, burst, segregation
etchant. Cleaned specimen should be macro etched porosity or looseness;
immediately. The acidic etch is more likely to b) Surface and Sub-surface Defect—Seam,
produce uneven etch than the caustic if the surface lap, segregation, crack, coarse grain ring;
is not precleaned. The caustic etch is an excellent
c) Miscellaneous Defects—Non-metallic
degreaser. Caustic etch also ensures a surface free
inclusions or dirt, extrusions defect;
from smeared metal, when examining direct chill
d) Fibre pattern of forged components; and
(DC) cast billets for porosity. In case of delay in
macro etching, specimen should be stored suitably e) Grain size, columnar grains, shell zone.
to avoid any contamination with oil and grease.
6 RECORDING OF RESULTS
3.6 Macro Etchant
The record shall contain full information on grade,
Macro etchant should be selected based on the alloy composition, melt number, form, condition of
purpose of examination and the type of alloy grades. supply and location examined.
Table 1 Macro Etchants
(Clause 3.6)
Sl Etchant Composition Method of Etching Alloy Types Applicable
No. (Parts by Volume)
(1) (2) (3) (4) (5)
i) Caustic etch 10 g sodium hydroxide Immerse specimen for Commercially pure
(NaOH) to 90 ml of water 5-15 minutes in solution aluminum and all
heated to 50-70°C, rinse other alloys including
with water, dip in 50 percent welding and brazing
nitric acid (HNO) solution joints made with this
3
to rinse again with water and alloy
dry
ii) Tucker’s reagent 45 parts concentrated Mix freshly, before use. Commercially pure Al,
hydrochloric acid (HCl) Immerse or swab specimen Al-Mg and Al-Mg-Si
15 parts concentrated for 10-15 s, rinse with warm alloys and many other
nitric acid (HNO) water and dry. If necessary alloys
3
15 parts hydrogen flouride repeat as much as required
(HF) (48) percent) until the desired effect is
25 parts water obtained
iii) Hydroflouric acid 1 part HF (48 percent) Requires fairly smooth, Al-Si alloy
9 parts water surface. Immerse until the
desired effect is obtained.
Rinse with hot water and

dry
2
IS 12573 : 2010
Table 1 (Concluded)
Sl Etchant Composition Method of Etching Alloy Types Applicable
No. (Parts by Volume)
(1) (2) (3) (4) (5)
iv) Poulton’s reagent 12 parts HCI (conc) Etch by brief immersion Pure Al, Al-Mn, Al-Si
5 parts HNO (conc) or by swabbing. Rinse in and Al-Mg-Si and
3
1 part HF (48 percent) cool water. Do not allow many other alloys
1 part water etchant/specimen to heat
during etching. The solution
may be premixed and
stored for long use
v) — 50 parts HCI (conc) Mix freshly, before use. High purity Al
15 parts HNO (conc) Cool the solution to
3
3 parts HF (48 percent) 10-15OC. Immerse specimen
5 parts FeCI for a few seconds, rinse in
3
(conc) solution cold water. Repeat until the
desired effect is obtained
vi) Zeerleder’s reagent 10g FeCl Etch at room temperature by High purity Al
3
100ml distilled water immersing for few seconds
0.5 ml HF (40 percent)
vii) — 60 ml HCl Immerse for few seconds Al-Cu alloys
40 ml HNO(70 percent) many other alloys

viii) — 10ml HCl Mix freshly. Immerse for All types of
30 ml HNO few seconds in solution at Al alloys
3
(70 percent) room temperature. Add
5g FeCI HCl last
3
ix) Keller’s reagent 20ml distilled water Mix freshly. Immerse for All types of
20ml HNO 1-3 min Al alloys, Al-Mn,
3
(70 percent) Al-Si, Al-Mg and
20ml HCl (38 percent) Al-Mg-Si
5ml HF (40 percent)
NOTES
1 Macro-etching should be carried out in containers which must be fairly resistant to the attack of etching reagents.
2 The prepared specimen should be put directly into the etching solution with surfaces to be examined either facing
or vertical to permit the gas generated to escape freely. The specimens being etched should not be too close to each
other or to the tank wall to avoid non-uniform etching. If specimens are too big to be etched by immersion, etching
should be done by swabbing.
3 If etching is required to be carried out above the room temperature, the etchant should first be heated to the required
temperature and then the specimen should be immersed in it.
4 The etching periods recommended in table are introduced only to guide. The time required to develop the desired
results may be determined by frequent examination of the specimen as etching proceeds. Actual etching time depends
on the factors which include method of manufacture, heat-treatment condition, alloy grade and surface preparation,
etc.

3
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Amendments Issued Since Publication
Amend No. Date of Issue Text Affected
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