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@PHDTHESIS{MagajiMehta:974704,
author = {Magaji-Mehta, Neeta},
othercontributors = {Zander, Brita Daniela and Spatschek, Robert},
title = {"{D}evelopment of a test method for testing stress
corrosion cracking of 7000 series aluminium alloys for
automotive applications"},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2023-11557},
pages = {1 Online-Ressource : Illustrationen},
year = {2023},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2024; Dissertation, Rheinisch-Westfälische
Technische Hochschule Aachen, 2023},
abstract = {In recent years, the Al-Zn-Mg-(Cu) aluminium alloys, also
known as the aluminium 7xxx series, have drawn considerable
attention in the automotive industry owing to its high
strength-to-weight ratio, making it a favored candidate for
light-weight automobile construction. Nonetheless, a
prominent challenge associated with these alloys is their
high risk of susceptibility to stress corrosion cracking
(SCC), which poses a significant risk of spontaneous
failures in the service life of an automobile. Stress
corrosion cracking is a complex phenomenon, involving the
simultaneous effect of a susceptible material, minimum
threshold stress, and a corrosive medium. Understanding the
effects of SCC with respect to automobile poses a serious
challenge due to the difficulty in predicting the influence
of critical factors, such as stress conditions and
environmental variations in the complex automotive
lifecycle. This work aims to scientifically analyse the
critical influencing factors, with a primary focus on their
synergistic interactions occurring in the complex automotive
lifecycle. This knowledge is then incorporated into
designing a novel accelerated SCC test, called the MBSC
test, which can test the SCC susceptibility of the 7xxx
alloys specifically for the automotive application. In this
thesis, a novel design approach, called Design for Six Sigma
(DFSS), was the primary design methodology. The DFSS is a
customer-centric product development methodology that
enables the designing of complex products or processes
systematically. The potential use of this methodology for
the development of future corrosion test methods was
assessed in this thesis. Four alloys, each with varying
contents of Zn, Mg and Cu, and varying temper treatments
were studied in this work, hence providing a range of SCC
susceptibility for testing. The effects of various factors
that are critical to SCC were clustered into environmental
and mechanical parameters and individually analysed. The
significant environmental parameters were investigated
through Design of Experiment. The significant mechanical
parameters were experimentally investigated on the three
chosen mechanical specimens and compared to the specimen
stresses occurring in critical in-service load conditions.
Finally, an outdoor exposure test was carried out, the
results of which were used to validate the Mercedes Benz
Stress Corrosion Test (MBSC). The results showed that using
the DFSS was advantageous in structuring the complex
analysis of the automotive lifecycle and efficiently
implementing it in the designing of the MBSC Test. A key
benefit of using this approach was the ability to study the
influencing parameters as an integrated whole rather than
studying them individually under carefully controlled
parameters, which is typically observed in most scientific
studies. A significant outcome of this thesis was
highlighting the potential of DFSS method as a standardized
framework for the development of future corrosion test
methods, particularly in the context of SCC tests. The
results of the individual and synergistic effects from the
above investigations served as the basis for the development
of a new test method, the Mercedes Benz Stress Corrosion
Test (MBSC). Studying the influence of environmental
parameters revealed critical parameters such as test
temperature and range of temperature variation in the MBSC
corrosion test cycle had a significant influence on the SCC
susceptibility. Moreover, anions and cations, NH4+ and NO3-
in the salt solution, had a significant influence on the
intergranular corrosion of the tested alloys. This in turn
acted as accelerator for initiation points for SCC, thus
increasing SCC susceptibility. Similarly, qualitative
analysis of the various mechanical specimens showed the
significant influence of mechanical parameters such as load
propagation mode, stress distribution and stress magnitude
on the SCC susceptibility of the tested alloys. Optimal
environmental and mechanical parameters for the MBSC test
were derived through this analysis. The results obtained
from the MBSC test were consequently validated by showing a
high correlation to the outdoor exposure test results.With
the help of the DFSS method, a novel test was created to the
needs of the automotive industry which can represent the SCC
corrosion susceptibility of 7xxx Al alloys during the
service life of a vehicle. The MBSC allows an exact
differentiation between SCC susceptible and non-susceptible
7xxx Al alloys. It should be emphasized that the MBSC test
can also identify only slightly susceptible alloys, which is
not possible with ASTM G47-98, a widely used standard test
for SCC susceptibility. The MBSC has a high significance for
the automotive industry, as it allows a differentiated
selection of 7xxx aluminium alloys for future automotive
designing.},
cin = {522710 / 520000},
ddc = {620},
cid = {$I:(DE-82)522710_20140620$ / $I:(DE-82)520000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2023-11557},
url = {https://publications.rwth-aachen.de/record/974704},
}
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