Grain Refinement of Al -Si Alloys by Nb-B Inoculation. Part 1: - PowerPoint PPT Presentation

“Grain Refinement of Al -Si Alloys by Nb-B Inoculation. Part 1: Concept Development and Effect on Binary Alloys. Part 2: Application to Commercial Alloys” 1

Grain refinement of Al-Si alloys by Nb-B inoculation M. Nowak L. Bolzoni N. Hari Babu Brunel Centre for Advanced Solidification Technology Brunel University London, UK The Charles Hatchett Award 2016 Lecture

Outline • Grain refinement in Al alloys with Al-5Ti-B • Concept development • Application to Al-Si cast alloys • Al-Nb-B master alloy • Comparative study between Al-Nb-B and Al-5Ti-B master alloys The Charles Hatchett Award 2016 Lecture

INTRODUCTION ALUMINIUM ALLOYS PROPERTIES • LOW DENSITY, 2.7 g/cc • GOOD MECHANICAL PROPERTIES • HIGH CORROSION RESISTANCE • HIGH THERMAL CONDUCTIVITY • LOW ELECTRICAL RESISTIVITY WROUGHT GRAIN ALLOYS REFINEMENT CAST (Al-Si) IMPROVEMENT FLUIDITY/CASTABILITY MECHANICAL PROPERTIES MACHINABILITY SURFACE QUALITY CHEMICAL HOMOGENEITY REDUCED SHRINKAGE POROSITY The Charles Hatchett Award 2016 Lecture

Factors determining grain size in as cast microstructure Nucleation & Growth Heterogeneous nucleation Growth Kinetics Homogeneous nucleation • Temperature • Atmosphere/Pressure Nucleation / growth rate • Growth restriction • Fragmentation • Cooling rate Under cooling ( D T ) D T = T L -T g T L The Charles Hatchett Award 2016 Lecture

E FFICIENT H ETEROGENEOUS N UCLEATION S ITES B ASE MATERIAL 1. High melting Temp 2. Low lattice mismatch (atom position matching) 3. Chemical stability (should not react with alloying elements) A B A N. Hari Babu et al., Nature Materials 2005;4:476 The Charles Hatchett Award 2016 Lecture

GRAIN REFINERS IN ALUMINIUM INDUSTRY Al Nuclei G RAIN R EFINEMENT : Al-Ti-B Al-Ti-C TiB 2 & Al 3 Ti Al 3 Ti Layer • Orientation Relationships TiB 2 Particle {111}Al//{112}Al 3 Ti//{001}TiB 2 <110>Al//<201>Al 3 Ti HREM image of Al/Al 3 Ti/TiB 2 interface <110>Al 3 Ti//<110>TiB 2 Source: B. J McKay M ODIFICATION : Sr modification of the Si morphology P to nucleate the primary Si particles The Charles Hatchett Award 2016 Lecture

Influence of Al-Ti-B grain refiner for Al-Si alloys Not effective Casting alloys Wrought alloys Ti-Si phase formation Mats Johnsson Patent, 2000 M. Johnsson, Influence of Si And Fe on the Grain-Refinement of Aluminum , Zeitschrift für Metallkunde, 85 (1994), 781-785

Ti reaction with Si in Al-Si alloys T. E. Quested et al, Mater. Sci. Technol. 22, 1126 (2006) Ti is consumed by the formation of TiSi 2 and TiSi The Charles Hatchett Award 2016 Lecture

Analogy between Al-Ti & Al-Nb phase diagrams Al 3 Ti Al 3 Nb The Charles Hatchett Award 2016 Lecture

L ATTICE M ISMATCH Al 3 Nb 0.384 nm Al Al (face centred cubic)

Low Lattice Mismatch – Coherent Interface Lattice mismatch ~0.9% The Charles Hatchett Award 2016 Lecture

Nb chemical stability with Si Nb – Ti – Si ternary system Nb – Si binary phase diagram J.C. Zhao et al., Materials Science and Engineering A 2004;372:21 Nb silicides form at higher temperature J.L. Muray and A. J. Alister, Bulletin than Ti silicides thus preventing poisoning of Alloy Phase Diagrams 1984;5:74

Addition of Nb metal powder to liquid Al Al-Nb 660 °C Al matrix Nb particles 20 mm 200 μ m 750 - 800 C Unreacted Nb metallic particulates The Charles Hatchett Award 2016 Lecture

Poor dissolution of Nb in liquid Al Nb 2 Al Nb NbAl 3 Nb 3 Al Nb 3 Al Nb 2 Al 20 μ m Requires high temperature for larger Nb particles and high concentrations The Charles Hatchett Award 2016 Lecture

Addition of Nb fine metal powder to liquid Al Nb- Superconductivity – 9K <45 m m To verify the Nb dissolution, magnetic moment vs temperature measured The Charles Hatchett Award 2016 Lecture

E FFECT OF Nb on CP Al CP-Aluminium 700ºC Al with Nb-B The Charles Hatchett Award 2016 Lecture

C OMPARISON OF Al-Ti-B AND Nb-B ON CP Al The Charles Hatchett Award 2016 Lecture

C OMPARISON OF Al-Ti-B AND Nb-B TO H YPOEUTECTIC B INARY Al-Si Alloys Al-1Si Al-2Si Al-4Si Al-5Si Al-6Si Al-8Si Al-10Si Reference 0.1wt.% Al-5Ti-1B 0.1wt.% Nb & B (powders) The Charles Hatchett Award 2016 Lecture

C OMPARISON OF Al-Ti-B AND Nb-B TO H YPOEUTECTIC B INARY Al-Si Alloys 700ºC Practical alloys composition The Charles Hatchett Award 2016 Lecture

Al-Si alloys for automotive applications Engine & transmission Components Crankcases Cylinder heads Intake manifolds Housings manual/automatic transmissions Source: VW Housings power transfer units VW Chassis Components Subframes Knuckles Steering housings Structural Components VW Body structures HL Instrument panels Door frames Wheels VW

Undercooling for Al-10Si alloy 0.3 o C/s Δ T Ref = 2.1ºC The Charles Hatchett Award 2016 Lecture

Reference Grain size up to 1 cm Δ T Ref = 2.1ºC The Charles Hatchett Award 2016 Lecture

Undercooling in the presence of NbB 2 /Al 3 Nb 0.3 o C/s Δ T Nb-B = 1.3ºC The Charles Hatchett Award 2016 Lecture

G RAIN STRUCTURE Reference Grain size up to 1 cm Nb-B Grain size: 2-3 mm Δ T Ref = 2.1ºC Δ T Nb-B = 1.3ºC

Cooling curves for Al-11Si (LM6) alloy a) b) 595 600 1 0.2 LM6+NGR 599 594 598 dT/dt 597 0.1 593 596 595 0 0.0 592 594 o C ] 593 o C ] 591 592 -0.1 T rec Temeprature [ 591 Temerature [ dT/dt dT/dt 590 Nb-B 590 -1 -0.2 T g =587 0 C 589 T nucl =588 0 C 588 589 587 -0.3 T g =587.5 0 C 586 588 T nucl = 588.8 0 C Δ T=2.5°C 585 -2 -0.4 584 587 583 T min =584.5 0 C LM6 Δ T=0.7°C -0.5 582 586 T min =586.8 0 C dT/dt 581 580 -3 585 -0.6 380 400 420 440 460 480 500 520 540 400 420 440 460 480 500 Time [ s ] Time [ s ] LM6 with Grain refiner addition LM6 20 mm

H YPEREUTECTIC B INARY Al-Si A LLOYS 700ºC Al-14Si α -Al α -Al dendrite dendrite 200 μ m 200 μ m The Charles Hatchett Award 2016 Lecture

H YPEREUTECTIC B INARY Al-Si A LLOYS - E UTECTIC Al-16Si 700ºC 20 μ m 20 μ m Al-18Si 20 μ m 20 μ m Al-27Si 20 μ m 20 μ m The Charles Hatchett Award 2016 Lecture

H YPEREUTECTIC B INARY Al-Si A LLOYS – P RIMARY S I Al-16Si 200 μ m 200 μ m Al-18Si 200 μ m 200 μ m Al-27Si 200 μ m 200 μ m The Charles Hatchett Award 2016 Lecture

Application of Nb-B grain refiner to Al-Si commercial alloys The Charles Hatchett Award 2016 Lecture

Commercial alloys tested with Nb-B GB USA Si Mg Mn Cu Ni Zn Fe LM6 A413 10.0-13.0 0.1max 0.5max 0.1max 0.1max 0.1max 0.6max LM13 336 10.0-13.0 0.2-0.4 0.5max 0.7-1.5 1.5max 0.1max 1max LM24 A380 7.5-9.5 3 max 0.5max 3.0-4.0 0.5 3 1.3max LM25 A356 6.5-7.5 0.2-0.6 0.3 0.2 0.1 0.1 0.5 9.99 0.005 0.005 0.0017 0.0044 0.005 0.09 10.98 0.268 0.21 2.134 0.068 0.778 0.83 6.06 0.275 0.265 2.725 0.0257 0.305 0.356 11.9 0.8 0.005 3.7 2 0.003 0.12 The Charles Hatchett Award 2016 Lecture

Nb-B Grain Refiner for Al-Si cast alloys  Highly effective for Al-Si alloys & Mg alloys  Fine & uniform grain structure  Grain size is less sensitive to cooling rate  Highly effective in sand casting cooling conditions  Reduced porosity & macro defects  Fine eutectic structure & intermetallics  Improved ductility & strength  Tolerant to Fe contamination  Recycling of Al-Si scrap The Charles Hatchett Award 2016 Lecture

C OMMERCIAL H YPOEUTECTIC Al-Si A LLOYS Reference Al-5Ti-1B Nb-B LM25 650ºC 500 μ m 500 μ m 500 μ m REFERENCE Nb-B Al-5Ti-1B LM24 900 α -Al grain size [µm] 800 LM6 500 μ m 500 μ m 700 500 μ m 600 500 LM24 400 LM6 300 200 LM25 100 500 μ m 500 μ m 500 μ m 0 600 610 620 630 640 650 660 670 680 690 Pouring temperature [°C] The Charles Hatchett Award 2016 Lecture

Nb-B Grain Refiner for Al-Si cast alloys  Highly effective for Al-Si alloys & Mg alloys  Fine & uniform grain structure  Grain size is less sensitive to cooling rate  Highly effective in sand casting cooling conditions  Reduced porosity & macro defects  Fine eutectic structure & intermetallics  Improved ductility & strength  Tolerant to Fe contamination  Recycling of Al-Si scrap The Charles Hatchett Award 2016 Lecture

~1200 m m Porosity Al-11Si (LM6) no addition ~200 m m Al-11Si (LM6) with Nb-B ~200 m m ~160 m m 10 mm The Charles Hatchett Award 2016 Lecture

Al-Nb-B Grain Refiner for Al-Si cast alloys  Highly effective for Al-Si alloys & Mg alloys  Fine & uniform grain structure  Grain size is less sensitive to cooling rate  Highly effective in sand casting cooling conditions  Reduced porosity & macro defects  Fine eutectic structure & intermetallics  Improved ductility & strength  Tolerant to Fe contamination  Recycling of Al-Si scrap The Charles Hatchett Award 2016 Lecture

E FFECT OF C OOLING R ATE 20 mm 20 mm 700ºC

E FFECT OF C OOLING R ATE Reference Nb-B inoculation 4500 4000 10000 α -Al grain size, d [µm] α -Al grain size, d [µm] 3500 d = 2072 ( dT/dt ) -0.34 3000 1000 2500 d = 514 ( dT/dt ) -0.14 2000 100 1500 1000 10 0.1 Cooling rate, dT/dt [°C/s] 1000 500 0 0 20 40 60 80 100 Cooling rate, dT/dt [°C/s] The Charles Hatchett Award 2016 Lecture