Tokyo Institute of Technology School of Materials and Chemical … · 2016. 12. 6. · Vertical...
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EXPERIMENTAL PROCEDURE Formation of periodical marks on Al-Mg alloy strip fabricated by vertical type high speed twin roll caster Tokyo Institute of Technology School of Materials and Chemical Technology Kumai-Muraishi laboratory INTRODUCTION RESULTS & DISCUSSIONS Surface / SEM-SEI & EPMA Al-Mg alloy has high heat crack susceptibility ➡ Many cracks & fractures even in twin roll casting Periodical marks on strip surface Muddy zone has many surface cracks unerasable by rolling Molten metal Roll Springs Strip Nozzle 20mm Muddy zone As cast As rolled Remained cracks Shiny zone CD CONCLUSIONS Vertical type high speed twin roll casting Problem of Al-Mg strip Hot rolling processes in conventional method are skipped ➡ Lower cost & energy consumption Rapid cooling results in finer microstructure ➡ Better mechanical properties OBJECTIVE Chemical composition [wt%] Al Mg Si Ti Fe Mn Cu Bal. 3.5~4.5 ~0.2 ~0.2 ~0.3 ~0.6 ~0.1 Casting temperature 665℃ Separating force 11kN Roll speed 60m/min Solidification length 100mm Initial roll gap 1mm Surface: SEM-SEI, EPMA Cross-section: OM etched by Weck’s reagent, Keller’s reagent Sample: Al-Mg alloy Casting condition Microstructural analysis 3 5 6 4 2 1 0 7 Al 80 60 70 50 90 wt% Mg 12 8 10 6 4 2 0 50μm 10μm What are periodical marks? How are periodical marks formed? What are periodical marks? How are periodical marks formed? 200μm Shiny Muddy Globular grain Solidification shell Fe Cross-section / OM Idea & Validation Al-Mg alloy (AC7A) strip can be fabricated by vertical type high speed twin roll casting Problem: Periodical marks on the strip “Muddy zone” has many cracks indelible even after rolling Periodical marks: Lower cooling rate ➡ Residual liquid was squeezed toward surface ➡ Muddy zone Formation of periodical marks: Periodical melt oscillation at the nozzle tips ➡ Periodical change of cooling rate Shiny Muddy Muddy Shiny 200μm Shiny Muddy Microstructural observation with SEM/OM Chemical analysis with EPMA Casting with differently shaped nozzle Detecting melt temperature at nozzle tip 20mm Insulator Steel plate Strip surface Globular grain region Lower cooling rate ➡ Residual liquid was squeezed to surface ➡ Muddy zone Higher cooling rate ➡ No residual liquid remained ➡ Shiny zone Thermocouple tips 655 660 665 670 675 680 1.5 2 2.5 Temperature, T/℃ Time from casting, t/s Melt oscillation at nozzle tip causes periodical change of cooling rate Ref. mitchellnissan.com http://www.omronap.co.th Application: car inner panel CD TD ND CD ND TD High Mg & Fe concentration on uneven surface Muddy zone High Mg & crack along grain boundary to surface ➡ Inverse segregation Muddy zone Thinner solidification shell ➡ Lower cooling rate 500μm No gap at nozzle tip erases periodical marks Temperature oscillation is detected only at nozzle tip RD Roll *Sampling interval: 500μs
Transcript of Tokyo Institute of Technology School of Materials and Chemical … · 2016. 12. 6. · Vertical...
EXPERIMENTAL PROCEDURE
Formation of periodical marks on Al-Mg alloy strip fabricated by vertical type high speed twin roll caster
Tokyo Institute of Technology School of Materials and Chemical TechnologyKumai-Muraishi laboratory
INTRODUCTION
RESULTS & DISCUSSIONS
Surface / SEM-SEI & EPMA
Al-Mg alloy has high heat crack susceptibility
➡Many cracks & fractures even in twin roll casting
Periodical marks on strip surface
Muddy zone has many surface cracks unerasable by rolling
Molten metal
Roll
Springs
Strip
Nozzle
20mm
Muddy zone
As cast As rolled
Remained cracksShiny zone
CD
CONCLUSIONS
Vertical type high speed twin roll casting Problem of Al-Mg strip
Hot rolling processes in conventional method are skipped
➡ Lower cost & energy consumption
Rapid cooling results in finer microstructure
➡ Better mechanical properties
OBJECTIVE
Chemical composition [wt%]
Al Mg Si Ti Fe Mn Cu
Bal. 3.5~4.5 ~0.2 ~0.2 ~0.3 ~0.6 ~0.1
Casting temperature665℃
Separating force11kN
Roll speed 60m/min
Solidification length100mm
Initial roll gap1mm
Surface: SEM-SEI, EPMA
Cross-section: OM etched by Weck’s reagent, Keller’s reagent
Sample: Al-Mg alloy Castingcondition
Microstructural analysis
3 5 64210 7
Al
8060 7050 90 wt%
Mg
128 106420
50µm
10µm
What are periodical marks?
How are periodical marks formed?
What are periodical marks?
How are periodical marks formed?
200µmShinyMuddy
Globular grain
Solidification shell
Fe
Cross-section / OM
Idea & Validation
Al-Mg alloy (AC7A) strip can be fabricated by vertical type high speed twin roll casting
Problem: Periodical marks on the strip “Muddy zone” has many cracks indelible even after rolling
Periodical marks: Lower cooling rate ➡ Residual liquid was squeezed toward surface ➡Muddy zone
Formation of periodical marks: Periodical melt oscillation at the nozzle tips ➡ Periodical change of cooling rate
ShinyMuddy Muddy Shiny
200µm
ShinyMuddy
Microstructural observation with SEM/OM
Chemical analysis with EPMA
Casting with differently shaped nozzle
Detecting melt temperature at nozzle tip
20mm
Insulator
Steel plateStrip surface
Globular grain region
Lower cooling rate ➡ Residual liquid was squeezed to surface ➡Muddy zone
Higher cooling rate ➡ No residual liquid remained ➡ Shiny zone
Thermocouple tips
655
660
665
670
675
680
1.5 2 2.5
Tem
per
atu
re, T
/℃
Time from casting, t/s
Melt oscillation at nozzle tip causes
periodical change of cooling rate
Ref. mitchellnissan.com http://www.omronap.co.th
Application: car inner panel
CD
TD
ND CD
ND
TD
High Mg & Fe concentration on uneven surface
Muddy zone
High Mg & crack along grain
boundary to surface
➡ Inverse segregation
Muddy zone
Thinner solidification shell
➡ Lower cooling rate
500µm
No gap at nozzle tip erases periodical marks
Temperature oscillation is detected only at nozzle tip
RD
Roll
*Sampling interval: 500μs
