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

Transcription

1 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

2 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

3 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

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

5 Nucleation / growth rate Factors determining grain size in as cast microstructure Nucleation & Growth Heterogeneous nucleation Homogeneous nucleation Growth Kinetics Temperature Atmosphere/Pressure Growth restriction Fragmentation Cooling rate T L Under cooling (DT) DT = T L -T g

6 EFFICIENT HETEROGENEOUS NUCLEATION SITES BASE 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

7 GRAIN REFINERS IN ALUMINIUM INDUSTRY GRAIN REFINEMENT: Al-Ti-B Al Nuclei 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 <110>Al 3 Ti//<110>TiB 2 HREM image of Al/Al 3 Ti/TiB 2 interface MODIFICATION: Sr modification of the Si morphology P to nucleate the primary Si particles Source: B. J McKay

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

9 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

10 Analogy between Al-Ti & Al-Nb phase diagrams Al 3 Ti Al 3 Nb

11 LATTICE MISMATCH Al 3 Nb nm Al Al (face centred cubic)

12 Low Lattice Mismatch Coherent Interface Lattice mismatch ~0.9%

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

14 Addition of Nb metal powder to liquid Al 20 mm 20 mm 20 mm Al-Nb 660 C Al-Nb 680 C Al-Nb 700 C Al-Nb 720 C 20 mm Al matrix 20 mm Nb particles 20 mm 200 μm C Unreacted Nb metallic particulates

15 Nb 2 Al Nb 3 Al Poor dissolution of Nb in liquid Al Nb 2 Al Nb NbAl 3 Nb 3 Al 20 μm Requires high temperature for larger Nb particles and high concentrations

16 Addition of Nb fine metal powder to liquid Al Nb- Superconductivity 9K To verify the Nb dissolution, magnetic moment vs temperature measured <45 mm

17 EFFECT OF Nb on CP Al CP-Aluminium 700ºC Al with Nb-B

18 COMPARISON OF Al-Ti-B AND Nb-B ON CP Al

19 COMPARISON OF Al-Ti-B AND Nb-B TO HYPOEUTECTIC BINARY 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)

20 COMPARISON OF Al-Ti-B AND Nb-B TO HYPOEUTECTIC BINARY Al-Si Alloys 700ºC Practical alloys composition

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

22 Undercooling for Al-10Si alloy 0.3 o C/s ΔT Ref = 2.1ºC

23 Reference Grain size up to 1 cm ΔT Ref = 2.1ºC

24 Undercooling in the presence of NbB 2 /Al 3 Nb 0.3 o C/s ΔT Nb-B = 1.3ºC

25 GRAIN STRUCTURE Reference Grain size up to 1 cm Nb-B Grain size: 2-3 mm ΔT Ref = 2.1ºC ΔT Nb-B = 1.3ºC

26 dt/dt dt/dt Temerature [ o C ] T nucl =588 0 C Cooling curves for Al-11Si (LM6) alloy a) b) LM6 dt/dt T rec ΔT=2.5 C T min = C LM6 Time [ s ] T g =587 0 C Temeprature [ o C ] T nucl = C ΔT=0.7 C T min = C LM6+NGR dt/dt Time [ s ] LM6 with Grain refiner addition Nb-B T g = C mm

27 HYPEREUTECTIC BINARY Al-Si ALLOYS Al-14Si 700ºC α-al dendrite α-al dendrite 200 μm 200 μm

28 HYPEREUTECTIC BINARY Al-Si ALLOYS - EUTECTIC Al-16Si 20 μm 20 μm 700ºC Al-18Si 20 μm 20 μm Al-27Si 20 μm 20 μm

29 HYPEREUTECTIC BINARY Al-Si ALLOYS PRIMARY SI Al-16Si 200 μm 200 μm Al-18Si 200 μm 200 μm Al-27Si 200 μm 200 μm

30 Application of Nb-B grain refiner to Al-Si commercial alloys

31 Commercial alloys tested with Nb-B GB USA Si Mg Mn Cu Ni Zn Fe LM6 A max 0.5max 0.1max 0.1max 0.1max 0.6max LM max max 0.1max 1max LM24 A max 0.5max max LM25 A

32 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

33 α-al grain size [µm] COMMERCIAL HYPOEUTECTIC Al-Si ALLOYS Reference Al-5Ti-1B Nb-B LM μm 500 μm 500 μm 650ºC LM24 REFERENCE Nb-B Al-5Ti-1B μm 500 μm μm LM LM6 400 LM LM μm 500 μm μm Pouring temperature [ C]

34 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

35 Al-11Si (LM6) no addition Porosity ~1200mm ~200mm Al-11Si (LM6) with Nb-B ~160mm ~200mm 10 mm

36 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

37 EFFECT OF COOLING RATE 20 mm 20 mm 700ºC

38 α-al grain size, d [µm] α-al grain size, d [µm] EFFECT OF COOLING RATE Reference Nb-B inoculation d = 2072 (dt/dt) d = 514 (dt/dt) Cooling rate, dt/dt [ C/s] Cooling rate, dt/dt [ C/s]

39 ΔNv / Nv ref [%] Number of grains, Nv [m -3 ] EFFECT OF COOLING RATE Nv(ref) 3.50E+10 Nv(Nb-B inoculation) 3.00E+10 ΔNv ΔNv / Nv(ref) 2.50E E E E E E Cooling rate, dt/dt [ C/s]

40 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

41 REFERENCE Al-Nb-B ADDITION Al-9Si-2Cu-0.7Mg-0.15Fe

42 A354 Alloy Condn. %Cu %Mg %Si %Fe %Mn %Ni %Zn %Pb %Sn %Ti %Sr Al-9Si-2Cu A354 CAST

43 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

44 Reduced Macro-porosity with Nb-B Al-11Si (LM6) with Al-5Ti-B 1 mm with Nb-B 1000µm 1 mm 1000µm 1 mm

45 Porosity Porosity Al-7Si alloy Porosity [ mm 2 ] Al-7Si+Al-5Ti-B ~ /cm 2 Tp1 test 700 O C Al-7Si + Nb-B 0 Aluminium Al-Ti-B Novel grain refiner Reduced porosity in Nb-B grain refiner added castings

46 Al-7Si alloy Without With Nb-B addition Fine grain structure Reduced porosity

47 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

48 Fine eutectic structure Al-11Si (LM6) with Nb-B

49 Eutectic Si [µm] Finer Eutectic Si - wider range of cooling rates LM6 (Reference) LM6 + Nb-B 20 μm HPDC 20 μm Cooling rate [ C/s]

50 Al-10Si With Nb-B

51 Reference (Al-13Si) with Nb-B

52 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

53 UTS [ MPa ] Improved strength & ductility 240 Al-11Si alloy Machined from cast bars Improved Crash performance Fatigue performance LM6 LM6+Nb-B Casting temp: Elongation [ % ] Gravity mould Melting temp: 800 o C o C yield 82.4 Mpa 102 Mpa

54 Al-13Si piston alloy Al-Nb-B

55 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

56 Control of Fe-intermetallics in Al scrap A354 A %Fe + 0.1%Nb-B 1% Fe Grain refiner to control Al-Fe-Si intermetallics Al 5 FeSi Al-Fe-Si large needle structure detrimental to mechanical properties

57 UTS (MPa) Recovery of properties in Fe-rich aluminium scrap Properties recovery through refinement of intermetallics Virgin alloy Virgin alloy with 1 wt% Fe impurity Reduced properties due to larger, needle structured intermetallics Elongation, 4D (%)

58 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 Re-melting & Fading study

59 Grain size, d [µm] FADING STUDY 680ºC d = 1.12 (t) R² = Contact time, t [min] LM6

60 Sedimentation height, h [cm] REQUIRED TIME TO SEDIMENT/FADE NbB2 Al3Nb AlB2 20 µm 15 µm 10 µm Φ or ρ Contact time, t [h]

61 Remelting Al-9Si-1.5Cu-0.6Mg-0.15Fe / RE-MELT No addition Al-Nb-B Addition 1 st Re-Melt ~ 3-4 mm 2 nd Re-Melt 3 rd Re-Melt 4 th Re-Melt

62 MASTER ALLOY DEVELOPMENT

63 Al-Nb-B Master Alloy 1. Nb metallic powder + KBF4 2. Addition of Nb metallic powder to diluted Al-B master alloy

64 MASTER ALLOY (METHOD 1) NbB 2 Al 3 Nb Al B Nb B Al Nb Al Al = at.% Nb = at.% O = 5.40 at.% Nb Al B Nb B

65 Al-2Nb-2B (METHOD 2) Al 3 Nb AlB 2-12 NbB 2

66 Al-4Nb-1B ON LM25 Reference 680ºC Nb-B (M.A.) Al-Nb-B (powders)

67 Al-4Nb-1B ON LM6 680ºC

68 Al-2Nb-1B ON Al-10Si

69 EFFECT OF Al-2Nb-2B ON UNDERCOOING FOR COMMERCIAL Al-Si ALLOYS

70 EFFECT OF Al-2Nb-2B ON COMMERCIAL Al-Si ALLOYS

71 RESULTS EFFECT OF Al-2Nb-2B ON COMMERCIAL Al-Si ALLOYS PISTON ALLOY (HYPER-EUTECTIC: 13 Wt.% Si) 740 C

72 EFFECT OF Al-2Nb-2B ON COMMERCIAL Al-Si ALLOYS 740 o C

73 EFFECT OF Al-2Nb-2B ON COMMERCIAL Al-Si ALLOYS 1600 Al-7Si (Ref) Al-7Si (Al-2Nb-2B) 1400 Al-8.5Si (Ref) Al-8.5Si (Al-2Nb-2B) α-al grain size [µm] Al-10.5Si (Ref) Al-10.5Si (Al-2Nb-2B) Cooling rate, dt/dt [ C/s]

74 Columnar grain structure Al-10 Si alloy - Direct Chill Cast Billets Fine (<0.5mm) equiaxed grains columnar Equiaxed Reference with Al-Nb-B Chill zone

75 Al-10Si DC billets Zone 1: chilled zone Zone 2: columnar crystals Zone 3: long columnar crystals Zone 4: equiaxed crystals Reference Nb-based compounds as heterogeneous nuclei Zone 1: chilled zone Inoculated Zone 2: very fine equiaxed crystals Zone 3: fine equiaxed crystals

76 DC-SIMULATOR

77 Comparative study between Al-Nb-B and Al-5Ti-B master alloys

78 Comparison between Ti-B and Nb-B Al-10Si Al-2Nb-B master alloy addition Al-5Ti-B master alloy addition ~ 4-5 mm ~ 300 µm 0.1% Nb 0.1%Ti

79 GRAIN REFINEMENT EFFICIENCY COMPARISON WHEEL ALLOYS (HYPO-EUTECTIC: 7 Wt.% Si) 740 C REFERENCE 0.1% Nb (AL-2Nb-2B) 0.2% MA (Al-5Ti-1B) 0.1% Ti (Al-5Ti-1B)

80 Summary Nb-B addition to Al-Si melt refines the grain structure of casting End-user benefits: Improved strength & ductility Lighter/thinner structures Homogeneous properties (thick & thin sections) Complex structures Tolerant to Fe contamination Closed loop recycling of scrap containing higher Fe Reduced shrinkage porosity - Improved soundness Component rejection ratio can be minimised