SOLDERING IN HIGH PRESSURE DIE CASTING (HPDC);

PERFORMANCE EVALUATION AND

CHARACTERISATION OF PHYSICAL VAPOUR

DEPOSITION (PVD) COATINGS

BY

STEFAN GULIZIA

A thesis submitted in fulfillment of the requirement for

admission to the degree of Masters of Engineering (Research)

in the School of Engineering and Science

Swinburne University of Technology

Hawthorn, Victoria, Australia

2008

Supervisors

Prof E.D. Doyle – Swinburne University of Technology

Dr M. Z. Jahedi – CSIRO Materials Science and Engineering

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ABSTRACT

During high pressure die casting (HPDC) of aluminium alloys there is a tendency for the

molten alloy to react with the steel die, core pins and inserts. This occurrence within the

HPDC industry is referred to as ‘soldering’. This is of concern to high pressure die casters

because of down-time, due to regular removal of the soldering, reduced die life and

degradation of casting quality. The reaction between the tool steel (usually H13) and the

molten aluminium involves inter-diffusion and the formation of intermetallic phases. To

remove this problem the possibility exists of applying a surface treatment to act as a

barrier between molten alloy and the die.

During the course of this research project several surface treatments were investigated

namely PVD (TiN, CrN, TiCN), Duplex PVD (TiN, CrN, TiCN) and Gas Nitriding for

soldering prevention during HPDC with aluminium alloy, and their results are compared

to uncoated core pins. The coating selection criterion was based on commercial

availability of surface treatments in Australia and suitability of coating properties with

H13 tool steel used in molten aluminium alloy (ADC-12).

One of the most important findings made during these experiments was the distinction

and characterization of build-up on the surface of PVD coatings. It was found that build-

up did not necessarily represent formation of intermetallics (soldering) for PVD surface

engineered core pins. It addition build-up did not grow in thickness as previously thought

and that build-up was influenced by high fluid flow and temperature during HPDC. The

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characterization of build-up was a fundamental important step in prolonging the

performance of PVD surface engineered core pins in HPDC.

The experimental results were confirmed by conducting in-plant HPDC trials at Nissan

Casting Plant Pty Ltd Australia. The results demonstrate that PVD coatings can improve

the resistance to soldering compared to conventional nitrided and un-coated core pins and

the need for polishing was eliminated.

Knowledge gained during this research program was transferred to NCAP and a guideline

for using PVD coatings in HPDC was prepared. A seminar on PVD coating for HPDC

was also given to the Australian die casting industry organized by the Australian Die

Casting Association (ADCA).

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ACKNOWLEDGEMENTS

This work was carried out at the school of Mechanical & Manufacturing Engineering,

Swinburne University of Technology under the supervision of: -

Professor E. D. Doyle

Head of Materials Technology Group, School of Engineering and Science,

Swinburne University of Technology

Dr. M. Z. Jahedi

Research Program Leader –Cold Spray & Tooling

CSIRO Materials Science & Engineering

I would like to sincerely thank my research supervisors for their valuable advise,

guidance, friendship, and assistance in research and editing of this thesis. I also wish to

express a special thanks to Prof. E. D. Doyle who regardless of the frequent work

interruptions overseas he continued to encourage and assist me to completion.

I would like to gratefully acknowledge the help, advice, and assistance from research staff

at CSIRO in particular Dr M. T. Murray, Dr D. T. Fraser, Dr Z. W. Chen, A. Yob, R.

Knight, K, Bousfield (dec) and Dr Y. C Wong from Swinburne University of Technology

for his valuable discussions during this research project.

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I also wish to express my thanks to staff at Nissan Casting Australia Plant for their helpful

discussions and assistance in conducting PVD coating validation trials and the use of their

production facilities over several months. In particular, K. Hooper (former GM), G.

Luxford (Managing Director), R. Bardsley, J. Law, M. Roberts, B. Blair, K. Porter, and

many others from the toolroom and production departments who assisted during the PVD

coating trials.

I also thank Surface Technology Coating Pty Ltd for providing the PVD coatings and

Hardchrome Engineering Pty Ltd for providing the gas nitrided samples.

Finally but not the least, I would like to say a special thanks to my best friend and wife

Gina, for her love, kindness, support, and patience even when I’m required to travel long

periods overseas often on short notice. To my children Christopher and Alexandra thank

you for your understanding and patience. God bless you guys.

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DECLARATION OF ORIGINALITY

The research work contained in this thesis to the best of my knowledge and belief, is

original except as acknowledged in the text. I hereby declare that I have not submitted this

material, either in whole or part, for any other degree at this or any other institution.

Stefan Gulizia

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LIST OF ASSOCIATED PUBLICATIONS

JOURNAL ARTICLES:

Gulizia, S., Doyle, E. D., & Jahedi, M. Z. “Performance Evaluation of PVD Coatings for

High Pressure Die Casting”, Surface Coating & Technology, Volume 140 (2001) 200-

2005

PEER REVIEWED CONFERENCE PAPERS:

Gulizia, S., Jahedi, M. Z., Doyle, E. D., Chen, Z. W. “Performance Evaluation of PVD

Coatings for High Pressure Die Casting”, Biennial Materials Conference of IMEA,.

Materials ‘98, 1998.

Gulizia, S., Jahedi, M.Z., & Doyle, E.D., Application of Duplex surface Treatments for

Aluminium High Pressure Die Casting Tools, Proceedings of the Tooling Industry Forum

Australian (TIFA) Melbourne, Australia, September 3-6, 2000, paper number 35

Gulizia, S., Jahedi, M.Z., & Doyle, E.D., “Relationship Between Draft Angle & Build-up

on PVD Coated Core Pins in High Pressure Die Casting”, Proceedings of the Australian

Die Casting Association International Conference, Melbourne, Australia, September 3-6,

2000, paper #35

INDUSTRY PUBLICATIONS:

Nissan Casting Australia Plant., ” Guidelines for Application of PVD Coatings for High

Pressure Die Casting of Aluminium alloys”., NCAP commercial-in-confidence, 2000

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TABLE OF CONTENTS

TITLE...………………………………………………………………………………….…I

ABSTRACT..………………………………………………………………………..…….II

ACKNOWLEDGEMENT....……………………………………………………………..IV

DECLARATION OF ORIGINALITY….………………………………………….........VI

LIST OF ASSOCIATED PUBLICATION....……………………………………...…....VI

JOURNAL ARTICLE....…………………………………….…………………...VI

PEER REVIEWED CONFERENCE PAPERS….…………………………….…VI

INDUSTRY PUBLICATION..……………………………………………….….VI

TABLE OF CONTENT..……………………………………………………………...V111

LIST OF TABLES..……………………………………………………………………...XI

LIST OF FIGURES....…………………………………………………………………...XII

ABBREVIATIONS.....……………………………………………………………….XVIII

CHAPTER 1: INTRODUCTION……………………………………………………….1

1.1 GENERAL.…………………………………………………………………….1

1.2 OBJECTIVES OF THE RESEARCH PROGRAM….………………….….…5

1.3 METHODOLOGY..…………………………………………………………...6

1.4 STRUCTURE OF THESIS..…………………………………………………..7

CHAPTER 2: EVALUATION OF PVD COATINGS IN IMMERSION TESTS

USING ALUMINIUM ALLOY (ADC-12)……………………………………….......…9

2.1 INTRODUCTION..…………………………………………………………....9

2.2 EXPERIMENTAL METHODOLOGY….…………………………………...11

2.2.1 DYNAMIC IMMERSION TEST FACILITY….…………………..11

2.2.2 SURFACE ENGINEERING IMMERSION SPECIMENS….…….13

2.2.3 EXAMINATION OF IMMERSION SPECIMENS….………….…15

2.3 RESULTS…………………………………………………………………….17

2.3.1 UNCOATED SPECIMENS………………………………………..17

2.3.2 GAS NITRIDED SPECIMENS……………………………………20

2.3.3 PVD COATED SPECIMENS……………………………………...21

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2.4 DISCUSSION………………………………………………………….……..25

2.5 CONCLUSION………………………………………………………….……31

CHAPTER 3: PERFORMANCE EVALUATION OF PVD COATINGS IN HIGH

PRESSURE DIE CASTING OF ALUMINIUM ALLOY (ADC-12)………….……..33

3.1 INTRODUCTION……………………………………………………….…...33

3.2 EXPERIMENTAL METHOD………………………………………….…….34

3.2.1 CASTING DIE…....………………………………………………..34

3.2.2 SURFACE ENGINEERING OF CORE PINS……………………..36

3.2.3 EXAMINATION OF CORE PINS………………………….……..38

3.3 RESULTS & DISCUSSION…………………………………………….…...38

3.3.1 CORE PINS & DIE THERMAL PROFILES………….…………..38

3.3.2 MEASUREMENT OF BUILD-UP FORMATION…...……….…..41

3.3.3 METALLOGRAPHIC ANALYSIS………………………….…….43

3.4 CONCLUSION………………………………………………………………50

CHAPTER 4: EVALUATION OF DUPLEX COATINGS IN HIGH PRESSURE

DIE CASTING OF ALUMINIUM ALLOY (ADC-12).……………………………....53

4.1 INTRODUCTION..…………………………………………………………..53

4.2 EXPERIMENTAL METHOD………………………………………………..54

4.2.1 CASTING DIE.……………………………….……………………54

4.2.2 SURFACE ENGINEERING OF CORE PINS………………….….54

4.2.3 EXAMINATION OF CORE PINS………………………………...56

4.3 RESULTS AND DISCUSSIONS………………………………………….…56

4.3.1 DUPLEX SURFACE TREATMENT OF CORE PINS…………....56

4.3.2 HPDC EXPERIMENTS…………………………………………....58

4.3.3 SEM MICROGRAPHS………………………………………….…59

4.3.4 SURFACE PREPARATION OF DUPLEX TREATMENTS…..…64

4.3.5 HARDNESS MEASUREMENTS……………………………….…65

4.4 CONCLUSIONS………………………………………………………….….66

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CHAPTER 5: METHOD TO CONTROL ‘BUILD-UP’ FORMATION ON PVD

TiN COATED BY CORE PIN DESIGN MODIFICATION...……….………………68

5.1 INTRODUCTION…………………………………………………………....68

5.2 EXPERIMENTAL METHOD………………………………………………..69

5.2.1 CASTING…………………………………………………….…….69

5.2.2 MATERIALS AND COATING…………………………………....69

5.2.3 EXAMINATION OF CORE PINS………………………………...69

5.3 RESULTS & DISCUSSIONS………………………………………………..71

5.3.1 EFFECTS OF DRAFT ON BUILD-UP…………………………....71

5.3.2 METALLOGRAPHIC EXAMINATION OF CORE PINS……..…74

5.3.3 EXAMINATION OF ALUMINIUM ALLOY CAST PRODUCT...79

5.4 CONCLUSIONS…………………………………………………………......85

CHAPTER 6: INDUSTRIAL EVALUATION OF PVD COATING IN HIGH

PRESSURE DIE COATING OF ALUMINIUM ALLOY (ADC-12).……………….86

6.1 INTRODUCTION…………………………………………………………....86

6.2 BACKGROUND INFORMATION…………………………………….……87

6.3 RESULTS………………………………………………………………….…89

6.4 CONCLUSIONS………………………………………………………….….93

CHAPTER 7: CONCLUDING REMARKS……………………………………….….94

REFERENCES………………………………………………………………………….97

APPENDIX A: GUIDELINES FOR USE OF PVD COATINGS IN HPDC….…...101

APPENDIX B: JOURNAL PAPER………………………………………………..…104

APPENDIX C: CONFERENCE PAPER 1.……………………………………….…111

APPENDIX D: CONFERENCE PAPER 2.……………………………………….…118

APPENDIX E: CONFERENCE PAPER 3.………………………………………….122

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LIST OF TABLES

Table 2.1 Composition of H13 Tool Steel and Aluminium Alloy ADC-12..……..……...14

Table 2.2 Showing Surface Roughness Values on Immersion Specimens……….……...15

Table 2.3 Composition of the three layers that characterizes soldering Sundqvist [10]…18

Table 3.1 Table Showing Surface Roughness of the Core Pins used in HPDC

experiments…………………………………………………………………..37

Table 3.2 Table Showing Properties of PVD Coatings [22] and Gas Nitrided Layer.…...37

Table 4.1 Table Showing Surface Roughness of the Core Pins used for Duplex

experiments…………………………………………………………………....56

Table 6.1 Results of industrial PVD surface treatments at NCAP on two automotive dies

showing large production savings and gains by eliminating the need to stop for

polishing and increased tool life (Ford Main Case)…………………………...91

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LIST OF FIGURES

CHAPTER 1: INTRODUCTION……………………………………………………….1

Figure 1.1 Pie chart showing breakdown of HPDC machine downtime at NCAP during

the year 1996/97 [4]…………………………………………………………...3

Figure 1.2 Photograph of NCAP toolmaker polishing an automotive transmission die

to remove soldering using pneumatic chisel and impregnated rubber-

grinding wheel………………………………………………………………...4

CHAPTER 2: EVALUATION OF PVD COATINGS IN IMMERSION TESTS

USING ALUMINIUM ALLOY (ADC-12)……………………………………….......…9

Figure 2.1 Immersion test apparatus used for molten aluminium alloy (ADC-12)

immersion tests……………………………………………………………....13

Figure 2.2 Schematic diagram showing dimensions of immersion specimens…………..14

Figure 2.3 SEM micrograph of uncoated H13 specimen immersed in aluminium alloy

for 2 hours showing the three layer above the H13 specimen surface

namely, inner compound layer, outer compound layer, and composite layer.

Above these layers is a much thicker layer of build-up of solidified

aluminium alloy (ADC-12)………………………………………………16

Figure 2.4 Binary phase diagram of Fe-Al system showing intermetallic phases that form

during immersion of H13 tool steel in molten aluminium alloy (ADC-

12)..…………………………………………………………………………..19

Figure 2.5 SEM micrograph of uncoated H13 specimen immersed in aluminium alloy for

2 hours showing the three distinct layers characterized as soldering at higher

magnification………………………………………………………………...19

Figure 2.6 SEM micrograph of a Gas Nitrided H13 specimen immersed in Aluminium

alloy for 2 hours showing the fragmented compound layer and porosity sub-

layer………………………………………………………………………… 20

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Figure 2.7 SEM micrograph of PVD-TiN coated H13 Tool steel immersed in molten

aluminium alloy (ADC-12) for 2 hours showing local areas of ‘swelling’

caused by soldering beneath the PVD coating…..…………………………...22

Figure 2.8 SEM micrograph of PVD-CrN coated H13 Tool steel immersed in molten

aluminium alloy (ADC-12) for 2 hours showing local areas of ‘swelling’

caused by soldering beneath the PVD coating…..……………………….…..23

Figure 2.9 SEM micrograph of PVD-TiCN coated H13 Tool steel immersed in molten

aluminium alloy (ADC-12) for 2 hours showing local area of ‘swelling’

caused by soldering beneath the PVD coating…...…………………………..24

Figure 2.10a SEM micrograph of PVD-TIN coated surface showing surface defects and

pinholes…..…………………………………………………………………..28

Figure 2.10b SEM micrograph of PVD TiN coating showing inside a pinhole at high

magnification exposing the H13 substrate material………………………….29

Figure 2.11 SEM micrograph at high magnification showing Chromium macro-particle

that survived testing and soldering beginning underneath it………………...30

CHAPTER 3: PERFORMANCE EVALUATION OF PVD COATINGS IN HIGH

PRESSURE DIE CASTING OF ALUMINIUM ALLOY (ADC-12)…………….…..33

Figure 3.1 Schematic Diagram of the Accelerated Test Die showing core pin position

and the Sequence of Events in an HPDC Cycle……………………………..35

Figure 3.2 Drawing showing typical dimensions of a core pins used for HPDC

experiments…………………………………………………………………..36

Figure 3.3 A graph of 50 HPDC cycles showing the core pin and bulk die temperature

profiles……………………………………………………………………….39

Figure 3.4 A graph of two HPDC cycles showing the core pin and bulk die temperature

profiles of two consecutive HPDC cycles. The temperature at the point of metal

injection, die open & close, and die cooling is shown…………………….…..40

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Figure 3.5 Aluminium-silicon phase diagram showing a eutectic temperature of 577°C

for 12.2 wt. % silicon. For aluminium alloy ADC-12 the silicon content is

11.5 wt% and the eutectic temperature would be slightly higher.…………...40

Figure 3.6. Photographs of the core pins after 50 HPDC cycles in the experimental die

showing the amount of soldering as a function of the surface modification

treatment. The top row shows core pins with a ground surface finish and the

bottom row shows the micro grit-blasted surface finish…………………….41

Figure 3.7. A graph generated using a computer image analysis showing the percentage of

area build-up on the core pins as a function of surface modification and

surface roughness after 50 HPDC cycles ...…………..……………………...42

Figure 3.8 A graph generated using a computer image analysis showing the percentage of

area build-up on the core pins as a function of surface modification in the

ground condition for 50 & 100 HPDC cycles………………………………..43

Figure 3.9a SEM micrograph showing intermetallic layers on a ground H13 tool steel

substrate after 50 accelerated HPDC cycles .………………………………..45

Figure 3.9b SEM micrograph showing fragmented nitrided layer on a ground substrate

after 50 accelerated HPDC cycles .………………………………………….46

Figure 3.9c SEM micrograph showing build-up on a PVD TiN coating on a ground

substrate after 50 accelerated HPDC cycle…………………………………..46

Figure 3.10a SEM micrograph showing build-up on a PVD TiN coating on ground

substrate after 100 accelerated HPDC cycles .……………………………....47

Figure 3.10b SEM micrograph showing build-up on a PVD CrN coating on ground

substrate after 100 accelerated HPDC cycles .……………………………....47

Figure 3.10c SEM micrograph showing build-up on a TiCN coating on ground substrate

after 100 accelerated HPDC cycles ...……………………………………….48

Figure 3.11a SEM micrograph showing build-up on a PVD TiN coating on a micro-

blasted substrate after 100 accelerated HPDC cycles .…………………..…..48

Figure 3.11b SEM micrograph showing build-up on a PVD CrN coating on a micro-

blasted substrate after 100 accelerated HPDC cycles …..…………………...49

Figure 3.11c SEM micrograph showing build-up on a PVD TiCN coating on a micro-

blasted substrate after 100 accelerated HPDC cycles …..…………………...49

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CHAPTER 4: EVALUATION OF DUPLEX COATINGS IN HIGH PRESSURE

DIE CASTING OF ALUMINIUM ALLOY (ADC-12).…………..……...53

Figure 4.1 Block diagram of the key process steps involved in producing duplex surface

treatments and the cleaning methods used for each set of core pins……...…55

Figure 4.2 Photograph of a failed duplex treated core pin (method 1) which was not

surface prepared prior to PVD coating. The black areas are where the PVD

coating has spalling from the substrate…..…………………………………..57

Figure 4.3 Relationship between surface roughness and percentage of area soldered/ built-

up after 50 HPDC cycles for un-coated, nitrided, PVD coated and duplex-

treated polished (method 2), and micro-grit blasted (method 30) core

pins…..……………………………………………………………………….59

Figure 4.4a Duplex TiN on a polished substrate after 50 accelerated HPDC cycles

showing black layer beneath the PVD coating……………………………...61

Figure 4.4b Duplex CrN on a polished substrate after 50 accelerated HPDC cycles

showing black layer beneath the PVD coating………………………………61

Figure 4.4c Duplex TiCN on a polished substrate after 50 accelerated HPDC cycles

showing black layer beneath the PVD coating………………………………62

Figure 4.5a Duplex TiN on a micro grit blasted substrate after 50 accelerated HPDC

cycles showing absence of black layer………………………………………62

Figure 4.5b. Duplex CrN on micro grit blasted substrate after 50 accelerated HPDC cycles

showing absence of black layer……………………………………………...63

Figure 4.5c. Duplex TiCN on micro grit blasted substrate after 50 accelerated HPDC

cycles showing absence of black layer………………………………………63

Figure 4.6 Block diagram of the three cleaning methods used for each set of core pins

and showing the most successful preparation method for duplex treatment

is by micro grit blasting……………………………………………………...64

Figure 4.9. Graph showing comparison hardness profiles for uncoated, nitrided,

PVD, & Duplex PVD surface treatments……………………………………65

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CHAPTER 5: METHOD TO CONTROL ‘BUILD-UP’ FORMATION ON PVD

TIN COATED BY CORE PIN DESIGN MODIFICATION...….………68

Figure 5.1. 3D surface profile of a PVD-TiN coated core pins with a (5.1a ) 3°

(5.1b ) 1.5° (5.1c ) 0.5°and (5.1d ) 0° draft angle, showing the distribution

and thickness of the build-up after 50 HPDC cycles (centre area of surface

profile represents directly in front of gate…………………………………...72

Figure 5.2. SEM micrographs of a cross sectioned PVD TiN coated pins with a

(5.2a) 3°, (5.2b) 1.5°, (5.2c) 0.5°and (5.2d) 0° draft angles after 50

HPDC cycles showing relationship with build-up thickness………………..75

Figures 5.3 Schematic diagrams showing the sequence of events during ejection of the

casting from the core pin, and the mechanism that reduces build-up thickness

with low draft angle (Figure 5.3a) compared to high draft angle (Figure 5.3b).

Note low clearance created by low draft angle rubs and polished build-up

during ejection.……………………………………………………….……...78

Figure 5.4. Photographs showing cross-sectioned aluminium alloy casting after 50

HPDC cycles produced with (5.4a) 3° (5.4b) 1.5° (5.4c) 0.5° and (5.4d) 0°

draft angles. Top image-showing side away from the gate and bottom image

the side facing the gate……………………………………………………….81

Figure 5.5 Schematic diagram representing molten metal directly impinging on the core

pin surface and the effects it has on ‘skin’ condition (porosity forming close to

the surface manifesting to build-up during ejection) compared to the opposite

side of the core pin (porosity forming some distance away)……………..…84

CHAPTER 6: INDUSTRIAL EVALUATION OF PVD COATING IN HIGH

PRESSURE DIE COATING OF ALUMINIUM ALLOY (ADC-12).……….………86

Figure 6.1 Photograph of ZY Side Cover casting showing Sensor boss and Parking

hole core pin position used for PVD Industrial trial…………………..……..88

Figure 6.2 Photograph of Ford Main Case casting showing position of small core pin

used for PVD Industrial trial….……………………………………..……….88

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Figure 6.3 Photograph of Ford main case die showing amount of build-up on PVD CrN

coated core pins after 31000 cycles……….…………………………………92

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ABBREVIATIONS

ADCA Australian Die Casting Association

ADC-12 Japanese Standard Aluminium Alloy

ASTM American Society for Testing and Materials

CSIRO Commonwealth Scientific Research Organization

EDX Energy Dispersion X-ray

HPDC High Pressure Die Casting

HRC Hardness Rockwell ‘C’ Scale

HVN Hardness Vickers Number

H13 Din 1.224 Tool Steel

MPa Mega Pascal

IMEA International Materials Engineering Australia

NADCA North American Die Casting Association

NCAP Nissan Casting Australia Plant

PACVD Plasma Assisted Physical Vapour Deposition

PVD Physical Vapour Deposition

Ra Roughness average value

SEM Scanning Electron Microscope

SOP Standard Operating Procedure

TIFA Tooling Industry Forum of Australia

µB Micro-grit Blasted

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