Project BFCleaner
BFCleaner— Borate Free Cleaners for Aluminum Alloys
State of the art – Background
Aluminum objects are commonly used in
everyday & everybody life. In order to avoid
corrosion of aluminium parts, a protective
treatment called “anodization” is required;
anodization is a controlled corrosion of the
component’s surface able to protect the part by
further corrosion propagation.
In particular, aluminium airplane components,
need an accurate corrosion protection as
consequence of the severe working conditions.
Anodizing process is an electro-chemical
process consisting of several steps: one of the
first step is the degreasing of the surface as
consequence
of
previous
production
operations. The degreasing products actually
on the market generally contain borates.
Borates must be limited in the waste water
exiting from the plant since they are not
permitted in discharged water. The anodizing
plants generally are equipped with a
physical‐chemical waste water treatment
system. However, this system is not able at all,
or with a very limited capacity, to remove
borates from waste water. At a recent
European
Diagnostics
Manufacturing
Association (EDMA) Meeting, several new
additions to the “Substance of Very High
Concern (SVHC) candidate list” were
discussed in relation to the Registration,
Evaluation, Authorization and restriction of
Chemicals Regulations 2007 (REACH). The
registration and review completed as part of
REACH has classified the Boric Acid CAS
10043‐35‐3 / 11113‐50‐1 as H360FD (May
damage fertility, May damage the unborn
child).
When cleaning aluminum parts, there are two
major tasks and one main risk:
1. remove any grease or solid soils or other
contaminants adsorbed or chemically bonded
to the surface of the parts from previous
operations.
2. remove the surface oxide film together with
these contaminants.
3. The risk of damaging/corroding material
surface thus reducing mechanical proprieties
and
particularly
fatigue
life
.
Some borate‐free agents are already available
on the market but the process window data are
merely focused on the degreasing efficiency
and not on the level of corrosion that such
cleaners may generate on the surface.
Objectives
Aim of the project was to develop two new
borate free agents to be compared with others
available on the market and with the one under
use in ITD plants in terms of cleaning efficiency
and absence of damaging of the parts.
In particular four new borate‐free agents
(cleaners) were analysed in term of capacity to
remove any grease or solid soils or other
contaminants like pencil inks adsorbed or
chemically bonded to the surface of the parts
from previous operations. Different borate‐free
formulations were tested and investigated
evaluating the cleaning efficiency in different
methods compared to formulations containing
borates and also evaluating the impact in term
of corrosion or damage of these new
formulations on two aluminium alloys. The two
aluminium alloys to be tested were selected
within the most critical ones in aeronautical
applications AA2024 clad and unclad.
In order to investigate the effect of Agent
Concentrations, processing Temperatures,
Immersion times and Contaminations types in
a limited number of trials, a partial Design of
Experiment Factorial Plan has been defined
and proposed. Initially, for the 2024 unclad, a
complete DOE plan was proposed. Then, for
the clad alloy, a reduced Factorial Plan was
proposed.
Description of work
The testing procedure, accordingly also to ITD
standards, followed the steps also reported in
Figure 1:
1. Measurement of specimen weight;
2. Contamination of the specimen with ink and
grease; a time interval of at least half an hour
and maximum two hours were applied in order
to dry the contaminants;
3. Measurement of specimen weight with
contaminations
and
computation
of
contaminations weight;
4. Preparation of cleaning solution in the tank
(5 liters). The solution tank is used for a single
temperature and concentration then it’s newly
produced in order to test another condition.
This means that a 5 liter solution is used to
clean between 3 to 5 specimens: three
specimens when only 2024 unclad was tested
(times of 5-15-30 minutes) while five
specimens were cleaned for the testing
conditions that required also 2024 clad alloy
testing (15-30 minutes);
5. Treatment of the specimen for the required
time;
6. Rising of the specimen with pure water;
7. Front (F) and Lateral (L) pictures of the
wetted specimen;
8. Visual inspection for detection of removal of
ink and grease and assignment of a 0 to 5
score (no removal 0, total removal 5);
9. Classification accordingly to ITD standards;
10. Specimen drying;
11. Measurement of specimen weight after
cleaning and computation of removed material
(contaminants and aluminum);
12. Picture of the dried specimen;
13. Execution of droplet test on greasedcontaminated side; definition of contamination
level;
14. Execution of droplet test on uncontaminated side; definition of contamination
level.
For the two most promising agents and the
reference one, Removal Rate Testing “Method
B” was performed in order to verify the
absence of relevant corrosion. The method
requires the following steps:
1. Cleaning of the identified specimen sheets
prior to determination of the removal rate;
2. The weight of the specimen sheets, which
were previously dried at (100 ± 5) °C and
cooled down in the desiccator, were
determined on an analytical balance to within 1
mg (G1 in g/dm2).
3. The specimen sheets were treated for (3600
± 5) s in the cleaning solution to be tested. The
specimen sheets were then rinsed thoroughly
and neutralized. The specimen sheets were
rinsed again thoroughly with fully desalinated
water and dried in hot air (e. g. drying
cupboard at 100 °C/30 min.).
4. After the specimen sheets were dried and
cooled down in the desiccator to room
temperature, the weight was determined on an
analytical balance (G2 in g/dm2).
5. Conversion of removal rate ”unilateral/min”
by means of eq.:
removal
rate
in
µm/min=(G1G2)x100/(2x2,7x60) with G1 initial weight
(g/dm2), G2 final weight (g/dm2), 2 for bilateral
exposition to cleaning agent, 2,7 g/cm3 for
specific weight of Al and 60 bath time in
minutes.
Finally, the specimens, (2024 clad and unclad)
treated following the Removal Rate Testing at
the maximum concentration levels of the
selected agents, were tested through grain
pitting procedure (ASTM F 2111 at 500X).
From all samples reported and described in
Table 3, metallurgical test specimens were cut
out following ASTM F 2111 procedure (see
Fig 2) and embedded in resin to obtain crosssections (face A was evaluated, Fig 2). After
mounting, samples were polished and
observed by means of extended pressure
scanning electron microscopy (EP-SEM) to
evaluate end grain pitting. Three repetitions
were prepared for each kind of treatment.
As results it was found that almost all cleaners
surprisingly acts as effective as reference one,
with two agents (Agent 1 available on the
market while Agent 2 developed within the
project) evidently producing an higher cleaning
efficiency compared to reference one. It was
also found that visual Inspection appears as
the best qualitative evaluation parameter
while % of removed material and droplet on
grease seems to be the most reliable
quantitative parameters for evaluation of
cleaning efficiency.
The two most promising agents and the
reference one were then tested in term of
Removal Rate Testing: it was found that
marginal material removal is achieved in all the
tested conditions. The worst condition was
obtained with Agent 1 (unclad alloy, maximum
concentration) that provided a removal rate
value only double with respect to reference
condition while optimal conditions (Agent 2, all
concentrations and Agent 1 low concentration)
provided removal rates comparable to
reference agent. In general unclad specimens
are more subjected to etching effect. As
previously stated, the Reference agent has a
minor cleaning effect and, as consequence, it
produced also the minimal removal rate for
both clad (0,0007 µm/min) and unclad (0,0014
µm/min) specimens. Concerning Borate free
agent 1, it produced the maximum Removal
Rate when maximum concentrations were
used (both on clad and unclad) while lower
values were found at minimal concentrations.
Instead Borate free Agent 2 showed an
average behaviour in term of Removal Rate
between reference and Agent 1 and a minor
influence of concentrations is proved. It has to
be noted that agent 1 passed the preliminary
evaluation
only
when
maximum
and
intermediate concentrations were adopted,
while the agent 2, developed within the
project , provided a good behaviour also at
lower concentrations.
After grain pitting analysis, it was found that
clad samples were free from end grain pitting
while unclad samples presented rare localized
attacks at a very initial stage with all the
selected cleaning agents and also with respect
to the Reference one.
Results
As conclusion, the project was able to identify
two new borate free cleaning agents able to
substitute the one nowadays in use and able to
guarantee: an higher cleaning efficiency, a
comparable level of corrosion and the absence
of grain pitting phenomena during grain pitting
test. The identified borate free cleaning agents
satisfies all the requirements of the REACH
standards in term of Substance of Very High
Weight of
specimen
Contamination
Drying
Picture of dryed
specimen
Weight after
contaminati
on
Weight
after
cleaning
Concern (SVHC) and are now all available in
the market.
Treatment of the
specimen
Pictures of
wetted specimen
Droplet test
Figure 1: Testing procedure
Figure 2: Comparison of cleaning efficiency on grease and ink contamination with different agents
2024 clad
2024 unclad
Reference
Agent
with
borate
Borate
free agent
1
-
Borate
free agent
2
Figure 2: BSE images of representative cross-sections of clad and unclad specimens treated with the
different agents.
Project Summary
Acronym :
BFCleaner
Name of proposal:
Borate Free Cleaners for Aluminum Alloys
Technical domain:
Metallic surface treatments
Involved ITD
Eco design
Grant Agreement:
296687
Instrument:
Clean Sky
Total Cost:
99 998€
Clean Sky contribution:
66 279€
Call:
SP1-JTI-CS-2011-01
Starting date:
1/2012
Ending date:
6/2013
Duration:
18
Coordinator contact details: Prof. Luca Tomesani, Viale Risorgimento 2, +39 051 2093425,
luca. Tomesani@unibo.it
Project Officer:
Paolo Trinchieri
Participating members:
Universita’ di Bologna, IT
Italtecno, IT
paolo.trinchieri@cleansky.eu