Ultrasonic Processing of Aluminum Alloys

165 Pages·2013·30.62 MB·English

Ultrasonic Processing of Aluminum Alloys

Liang Zhang
The research described in this thesis was performed in the department of Materials Science
and Engineering, at Delft University of Technology

This research was carried out under project number M11.5.11419 in the framework of the
Research Program of the Materials innovation institute (M2i) in the Netherlands
(www.m2i.nl)
Ultrasonic Processing of Aluminum Alloys

Proefschrift

ter verkrijging van de graad van doctor
aan de Technische Universiteit Delft,
op gezag van de Rector Magnificus prof. ir. K.C.A.M. Luyben,
voorzitter van het College voor Promoties,
in het openbaar te verdedigen op woensdag 13 maart 2013 om 15.00 uur

door

Liang Zhang
Master in Materials Science and Engineering
University of Science and Technology Beijing, China
geboren te JiangXi , China
Dit proefschrift is goedgekeurd door de promotor:
Prof. ir. L. Katgerman
Prof. dr. D. G. Eskin

Samenstelling promotiecommissie:

Rector Magnificus, voorzitter
Prof. ir. L. Katgerman, Technische Universiteit Delft, promotor
Prof. dr. D. G. Eskin, Brunel University, U.K., promotor
Dr. A. Miroux, Materials Innovation Institute
Prof. M. R. Jolly, Cranfield University, U.K.
Prof. L. Zhuang, University of Science and Technology Beijing, China
Dr. R. Sauermann, Aleris Rolled Products, Germany
Prof. dr. I. M. Richardson, Technische Universiteit Delft
Prof. dr. ir. J. Sietsma, Technische Universiteit Delft, reservelid

Keywords: Ultrasonic processing, Solidification, Aluminum alloys, Microstructure, Casting
properties

ISBN 978-90-77172-89-6
Copyright © 2013 by L. Zhang
All right reserved. No part of the material protected by this copy right notice may be
reproduced or utilized in any form or by means, electronical or mechanical, including
photocopying, recording or by any information storage and retrieval system, without
written permission from the author.
Contents

Chapter 1 Introduction...................................................................................1
1.1 Aluminum alloys and their casting...................................................2
1.2 Casting properties of aluminum alloys.............................................2
1.2.1 Microstructure............................................................................................2
1.2.2 Macrosegregation.......................................................................................4
1.2.3 Solidification shrinkage and thermal contraction.......................................5
1.2.4 Fluidity.......................................................................................................7
1.2.5 Hydrogen Porosity.....................................................................................9
1.3 Ultrasonic processing......................................................................10
1.3.1 Background of ultrasonic processing in liquid metals.............................10
1.3.2 Application of ultrasonic processing in castings.....................................10
1.4 Thesis objectives and outline..................................................................14
References...............................................................................................15

Chapter 2 Effect of ultrasonic processing on as cast structure in aluminum
alloys containing Zr and Ti..........................................................................23
2.1 Introduction.....................................................................................24
2.2 Experimental procedure.........................................................................25
2.3 Formation of primary intermetallics under UST.........................................27
2.3.1 Effect of UST on primary intermetallics in Al-Ti and Al-Zr-Ti alloys...27
2.3.2 A possible nucleation behavior of primary intermetallics under UST....30
2.4 Role of solutes and transition metals in grain refinement under UST .............34
2.4.1 Formation of intermetallics and related grain refinement in an Al-Zr-Ti
alloy..................................................................................................................34
2.4.2 Influence of Zr and solute on ultrasonic-aided grain refinement.............38
2.5 Conclusions........................................................................................42
References...............................................................................................43

Chapter 3 Effect of ultrasonic processing on as cast structure in aluminum
alloys of eutectic systems.............................................................................45
3.1 Introduction.....................................................................................46
3.2 Formation of microstructure in binary Al-Fe and Al-Mn alloys.....................47
3.3 Formation of microstructure in binary Al-Si alloy.......................................52
3.3.1 Effect of UST on microstructure in hypo-eutectic Al-Si alloy................54
3.3.2 Effect of UST on microstructure in near-eutectic Al-Si alloy ................57
3.3.3 Effect of UST on microstructure in hyper-eutectic Al-Si alloy...............58
3.4 Ultrasonic application in a commercial piston Al-Si alloy............................60
3.5 Conclusions........................................................................................63
References...............................................................................................63

Chapter 4 Parameters of ultrasonic processing............................................65
4.1 Introduction.....................................................................................66
4.2 Power of ultrasonic generator.................................................................67
4.3 Initial sonotrode temperature..................................................................70
4.4 The temperature of ultrasonic treatment ..................................................72
4.5 Holding time after UST.........................................................................75
4.6.1 Cooling rate during solidification..........................................................76
4.6.1 Ultrasonic treated grain structure under different cooling rate................76
4.6.2 Discussion...............................................................................................78
4.7 Conclusions........................................................................................81
References...............................................................................................82

Chapter 5 Application of ultrasonic processing in DC casting....................83
5.1 Introduction.....................................................................................84
5.2 Experimental procedure.........................................................................85
5.3 Ultrasonic processing applied in the launder during DC casting.....................86
5.3.1 Water-model optimization of UST..........................................................86
5.3.2 UST in the optimized launder design......................................................90
5.4 Ultrasonic processing applied in the hot top and extensional analysis ............91
5.4.1 UST applied in the hot top......................................................................91
5.4.2 Modification of flow pattern during DC casting.....................................93
5.4.2.1 Experimental results and computer simulation....................................95
5.4.2.2 The evolution of grain structure in transition region............................98
5.4.2.3 The relative movement of solid and liquid phase in slurry zone..........99
5.4.2.4 Solidification shrinkage-driven flow in mushy zone..........................100
5.5 Conclusions......................................................................................104
References.............................................................................................105

Chapter 6 Effect of ultrasonic processing on thermal contraction during and
after solidification......................................................................................107
6.1 Introduction...................................................................................108
6.2 Experimental procedure.......................................................................108
6.3 The contraction behavior under UST during solidification..........................112
6.3.1 Effect of transition metals Zr and Ti.....................................................112
6.3.2 Effect of the temperature of UST..........................................................119
6.4 Factors affecting thermal contraction after solidification ..........................122
6.4.1 Decreasing of TCC at high temperature caused by UST.......................122
6.4.2 Solid thermal contraction at low temperature.......................................126
6.4.3 Role of gas precipitation in the solid state on TCC...............................126
6.5 Conclusions......................................................................................129
References.............................................................................................129

Chapter 7 Fluidity of aluminum alloy melts under UST and ultrasonic
degassing....................................................................................................131
7.1 Introduction...................................................................................132
7.2 Experimental procedure.......................................................................132
7.2.1 Fluidity test procedure...........................................................................132
7.2.2 Degassing test procedure.......................................................................134
7.3 The fluidity of molten Al alloy under UST..............................................135
7.3.1 Effect of grain structure on the fluidity.................................................135
7.3.2 Effect of oxide inclusions on the fluidity..............................................137
7.4 Degassing effect caused by UST .........................................................139
7.5 Conclusions......................................................................................143
References.............................................................................................143

Chapter 8 Concluding remarks...................................................................145
8.1 Concluding remarks......................................................................146
8.2 Outlook............................................................................................148

Summary...................................................................................................149
Samenvatting............................................................................................151
List of publications...................................................................................153
Acknowledgements...................................................................................155
Curriculum Vitae.....................................................................................157
Chapter 1 Introduction

Chapter 1

Introduction

1
Chapter 1 Introduction
1.1 Aluminum alloys and their casting
Nowadays, aluminum alloys are not strange and mysterious materials in our daily life. They
are widely used in many fields due to their good corrosion resistance, low density, high
strength-to-weight ratio and high fracture toughness [1, 2]. Depending on the alloying
elements added to aluminum, different types of aluminum alloys can be obtained, each of
them having their own superior performance in many specific areas. For instance, Al-Cu
alloys of the 2xxx series and Al-Zn-Mg-Cu alloys of the 7xxx series are usually used in
aerospace industry because of the relatively high strength. Al-Mg alloys of 5xxx series with
good corrosion resistance are very suitable for applications in corrosive atmospheres, e.g.
construction and shipbuilding. Al-Si casting alloys and Al-Mg-Si alloys of 6xxx series are
widely used in automotive industry due to their good castability, welding ability and
mechanical properties.
The demand for aluminum alloys is still growing. But more importantly, it is accompanied
by an increasing requirement for properties of aluminum products. Although several
techniques related to deformation processing and heat treatment are developed to meet
more and more stringent property requirements, the most important premise for applying
these techniques is a high initial quality of as-cast products. Therefore, a perfect casting
without defects has been the goal of engineers and foundry workers now, as it was for
centuries.
Aluminum casting can be generally classified as shape casting or ingot/billet casting. Shape
casting, such as pressure-assisted die casting, investment casting and gravity casting, is
used for producing shaped components. Ingot casting mainly produces ingot or billet for
further deformation processing, for instance, extrusion, stamping, or rolling .etc. The most
common used ingot casting technology is direct chill casting (DC casting).
Several types of casting defect can occur when casting is preformed improperly in both
shape casting and ingot casting, for instance, cracking, macrosegregation and porosity.
These defects are detrimental to the properties of as-cast products, as well as the quality of
semi- or finished products during further deformation. Therefore, the casting properties of
aluminum alloys are crucial to determining the final quality of aluminum alloy products.
1.2 Casting properties of aluminum alloys
1.2.1 Microstructure
Microstructure control in aluminum casting has been a topic of study for many decades.
The size and distribution of primary intermetallics, dendrite cell size or dendrite arm
spacing, equiaxed grain size and occurrence of columnar grains are crucial for determining
the final quality of casting products [3, 4].
Among these microstructural features, grain structure is of great importance, since the yield
strength is directly related to the final grain structure of alloys [5]. In addition, a fine and
uniform distribution of equiaxed grains is well known to benefit many other mechanical
and technological properties of aluminum alloys, such as increasing fracture toughness and
ductility, as well as improving the casting quality by minimizing shrinkage, hot tearing and
2