Effect of material and processing parameters on the morphology of aluminium foams produced by the PM route [Elektronische Ressource] / vorgelegt von Ahmed Hamed Ibrahim

Ahmed Ibrahim

Informations

• Publié par: friedrich-alexander-universitat_erlangen-nurnberg
• Publié le: 01 janvier 2005
• Nombre de lectures: 16
• Langue: English
• Poids de l'ouvrage: 10 Mo

Extrait

Effect of Material and Processing
Parameters on the Morphology of
Aluminium Foams Produced
by the PM Route







Der Technischen Fakultät der
Universität Erlangen-Nürnberg


zur Erlangung des Grades


D O K T O R - I N G E N I E U R


vorgelegt von


Ahmed Hamed Ibrahim


Erlangen – 2005











































Als Dissertation genehmigt von
der Technischen Fakultät der
Universität Erlangen-Nürnberg

Tag der Einreichung:20.06.2005
Tag der Promotion: 29.08.2005

Dekan: Prof. Dr. A. Winnacker

1. Berichterstatter: Prof. Dr.-Ing. R.F. Singer
2. Berichterstatter: Prof. Dr. rer. nat. H. Mughrabi iiiAbstract
ABSTRACT

There have been increased technological developments in the production of alumi-
num foams. Both physical and mechanical properties of aluminum foam are not only
controlled by their composition, but are affected significantly by cell structure. The
latter is strongly affected by the initial pore form. The state of the art is an approach
to understand the nucleation and foam evolution. The foaming metal powder com-
pacts (PM process) is employed. The influence of foaming parameters on the evolu-
tion of foam morphology is investigated in order to explain some surprising observa-
tions, i.e. the role of oxide in foam stability and the relation between cell wall thick-
ness, uneven cell wall and the size of oxide fragment, etc. The effects of blowing
agent content, blowing agent particle size, heating rate and in situ micro pores on the
nucleation and the final foam structure are studied. Particular attention is devoted to
the nucleation and its effects on the property of the matrix and also the correlation
between nucleation and the final foam structure. The employed blowing agent is in-
vestigated by DSC and TGA in both air and argon atmospheres. The results reveal
that the finer blowing agent evolves hydrogen earlier than the coarse one. Metal-
lographic observation and micro probe analysis of the air atomized aluminum powder
show that the aluminum oxide phase is also within aluminum particles.
Metallographic investigation, electronic picture analysis (Image C) and micro com-
puter tomography are employed to study the underlying material and the Al foams.
The produced foam is characterized by various parameters, form factor, relative den-
sity, mean material thickness, gas/metal interface length per unit area and maximum
foam expansion. The foam morphology reveals that final foam structure depends on
the initial pore form. Low amounts of blowing agent content, finer blowing agent par-
ticle size, higher heating rates and in situ micro pores lead to finer foam structure.
The improvement of foam structure results in finer blowing agent particle size at the
expense of the maximum foam expansion, the finer the smaller maximum expansion.
The addition of 2 wt. % Zn particles less than 40 µm in size improve the foam struc-
ture by inducing micro pore within solid precursor and crack suppression.
Nucleation effects on the matrix properties could then be explained. If the nucleation
takes place in solid precursor it leads to crack and the final foam structure looks like
cracks opening and the material stretching. However, if the matrix is liquid the size of
oxide fragments is governs the thickness of cell wall.

ivAcknowledgement
ACKNOWLEDGEMENT

Praise to Allah, the Cherisher and Sustainer of the World; Most Gracious, Most Mer-
ciful; Master of the Day of Judgment.
I am also to express my deep appreciation to my major Professor Dr.-Ing. Robert F.
Singer for his continuous encouragement, good humor and support to carry out my
Ph.D. work at WTM-Erlangen.
I would like to thank the members of the thesis committee; Prof. Dr. rer. nat. H.
Mughrabi, Prof. Dr. Köken and Prof. Dr. H. Meerkamm for their valuable comments
on the thesis.
I wish also to express my sincere gratitude for Dr.-Ing. Carolin Körner for her con-
tinuous guidance and encouragement during my work.
Special thank are to M. Arnold who taught me the first lesson on PM metal foam pro-
duction and characterization. I take pride in mentioning the marvelous companion-
ship of my MMC group. I thank H. Wiehler, M. Öchsner, V. Braeutigam, M. Hirsch-
mann, T. Euteneuer, M. Brunnbauer for their suggestions. I am appreciative to the
metallography assistant group; Mr. Nigge, Ms. Grembler, Ms. Röhl and Ms. Zinn for
their helpful attitude and suggestions. I acknowledge P. Randelzhofer for his assis-
tance with the DSC and TGA analysis and R. Schriefer for his helpful attitude. I thank
Ms. A. Duprée and Ms. I. Hilpert for their help. I take the opportunity to acknowledge
the friendly help rendered by people in the WTM institute, especially Dr.-Ing S. Rosi-
wal, Dr.-Ing. A. Volek, C. Rottmair, C. Bareiß, M. Perle, A. Glaser, M. Rüffer, A.
Schade, Mr. Beyer, Mr. Reichelt, Mr. Neuner, Ms. Strunz, M. Fraunstein, Mr. Kobri-
ger. I am highly grateful to Rauf O. Saleh and S. Elgazzar, A. Nassar, A. Bnikenanh
and Shaban for their help.
The author gratefully acknowledge; the M.H.E.-Egypt, WTM-Erlangen University Er-
langen-Nürnberg and DFG for supporting this work and financial support.
I must say special thanks to my parents who graciously instilled in me the value of
education and supported me throughout my education. Finally, thanks to my wife
who attended to my children and to my children for being always behind me.

Contents v
CONTENTS
ABSTRACT iii
ACKNOWLEDGEMENT iiv
LIST OF FIGURES vii
1....INTRODUCTION...................................................................1
2....LITERATURE........................................................................3
2.1 Metal Foam.......................................................................................................3
2.1.1 Foaming Methods......................................................................................3
2.1.2 Foam Structure..........................................................................................8
2.1.3 Metal Foam Stabilization .........................................................................10
2.2 Powder Metallurgy Process ............................................................................13
2.2.1 Nucleation and Structure Evolution..........................................................14
2.2.2 Blowing Agent17
2.2.3 Processing Parameters ...........................................................................19
2.2.4 Stabilization .............................................................................................20
2.3 Additive Elements in Powder Metallurgy.........................................................22
2.3.1 Basic Consideration.................................................................................22
2.3.2 Al-Zn System ...........................................................................................24
3....EXPERIMENTAL ................................................................26
3.1 Preparation of Precursor Foamable Material ..................................................26
3.1.1 Raw Materials..........................................................................................26
3.1.2 Mixing Process ........................................................................................28
3.1.3 Pressing...................................................................................................28
3.1.4 Thermal Analysis .....................................................................................30
3.2 Foaming Process............................................................................................31
3.2.1 Furnace Foaming31
3.2.2 Induction Foaming ...................................................................................32
3.3 Metal Foam Characterization..........................................................................33
3.3.1 Metallographic Investigation ....................................................................33
3.3.2 Chara