Magnesium Alloy Development for High

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MAGNESIUM USAGE BY MARKET (End of 2002) MAGNESIUM ALLOY DEVELOPMENT FOR HIGH-TEMPERATURE AUTOMOTIVE APPLICATIONS ALUMINUM ALLOYING 146 K MT 40% OTHERS including Mihriban Pekguleryuz gravity casting & McGill University MAGNESIUM wrought alloys (mainly Metals & Materials Engineering DIECASTING aerospace) Automotive ALLOYS 20 K MT & electronics 128 K MT DESULF. 5 % industries 57 K MT 35 % CHEM ICAL, ELECTRO- 16% CHEM ICAL, METAL January 2004 REDUCTION NODULAR IRON TOTAL : 365 K metric tons 14 K MT 4 %

AUTOMOTIVE USE OF MAGNESIUM AUTOMOTIVE USES OF MAGNESIUM

Growing use of magnesium in automotive CURRENT USE: INTERIOR MID-TO-LONG-TERM • Growing use of magnesium in automotive COMPONENTS applications in the 90’s e.g. I nstrument Panel, BODY steering wheel e.g Inner door panel, pillar structures - Stiffness, high ductility - Wrought products (formability) • valve covers to steering wheels, - Energy absorption - Structural casting alloys (ductility) instrument panels, AM alloys R- equires new alloys and processes seat-frames.

STEEL 50lb-Mg 18lb CHASSIS e.g. Wheel, suspension arm SHORT TERM : POWERTRAIN - Strength e.g. Transmission case, engine parts - High ductility, fatigue - Creep resistance (150-200C) - Corrosion resistance - Yield strength -R equires new alloys AZ91D - Corrosion resistance AM60, AM50, AM20 - Mg-Al-RE & Mg-Al-Si Requires new alloys Mg-9Al-1Zn Mg-Al-Mn alloys

ALLOY DEVELOPMENT ALLOYING BEHAVIOR OF MAGNESIUM FOR MAGNESIUM HIGH-TEMPERATURE APPLICATIONS FOR MAGNESIUM HIGH-TEMPERATURE APPLICATIONS Strength -- solid solution hardening & second phase hardening, PHASE I: 1992-1997 HUME-ROTHERY RULES - Atomic size ratio (15%) Development of Industrial Trials d Mg = 3.2 Å Learning preliminary alloys Li, Al, Ti, Cr, Zn, Ge, Y, Ce, Zr, Nb, Mo, Pd. Ag, Cd, In, Sn, Sb, Te, Nd, Hf, W, Re, Os, Pt, Au, Hg, Tl, Pb, Bi, Alloying & creep ITM Alloy

behavior of IMRA Alloy - Similar Crystal Structure Mg and its alloys Honda Alloy - Similar Crystal Structure Zn, Cd (%0.9)

PHASE II: 1998-2003 - Relative Valency Effect Group II - Group VII Commercial Prototyping & Development of alloys & evaluation improved alloys - Electro-negativity applications Compound formation

BMW engine block Noranda Alloys GM Alloy * M. Pekguleryuz, M. Avedesian “Magnesium Alloying-Some Metallurgical Aspects,” DSM Alloy Magnesium Alloys and Their Applications, DGM, 1992, pp. 213-220

1 Mg-Al & Mg-Al-Zn ALLOYS ALLOYING BEHAVIOR OF MAGNESIUM AZ91, AM20, AM50, AM60 casting alloys Precipitation hardening alloys Good R.T strength & ductility - Elements that Increase both Strength and Ductility

AZ31, AZ61 wrought alloys LOW CREEP RESISTANCE

Strength Criterion : Al, Zn, Ca, Ag, Ce, Ga, Ni, Cu, Th, Y AZ80 forging alloy Ductility Criterion : Th, Y, Ga, Zn, Ag, Ce, Ca, Al, Ni, Cu

- Elements that Increase Strength at the Cost of Ductility

Sn, Pb, Bi, Sb

- Elements that Increase Ductility but not Strength

Cd, Tl, Li, Mn

- Creep Mg17Al12 RE, Y, Ca, Cu, Th, Ag

CREEP DEFORMATION

CREEP -- THE TIME DEPENDENT STRAIN CREEP STRENGTH OF Mg DIECASTING ALLOYS •slow, continuous deformation with time.  = f() elastic/plastic deformation,  = f(, T, t) creep deformation Due to the thermally activated stress component (short range component)

) )  =  u + * a a P P  =  u + * M M ( (

s s CREEP RATE s s e e r r

t strain rate at a given stress is temperature t S S sensitive. Ý = A e (-q/kT). e(*/kT)

n Dislocation Creep Ý = A  e (-Q/RT) dislocation intersection, dislocation climb, movement of dislocation atmospheres, cross-slip, grain-boundary shear.

Diffusion-Creep Ý = B  e (-Q/RT) fast diffusion paths (dislocation cores or GB) or bulk diffusion (vacancy and interstitial) Temperature (C) (qd or qs) T> 0.3 Tm

CREEP MECHANISMS--What can be Thermally Aided ? CREEP BEHAVIOR OF Mg DIECASTING ALLOYS • Dislocation Intersection - work required to force a dislocation 2 through the stress field of another can be thermally aided. Ý = A e [-(qi - *b l)/kT] Mg single crystals AZ91D, AS21, AE42

• Activated Cross Slip - Thermally activation to unite partial q =100 kJ/mol dislocations and to breakdown into partials on different for high stacking fault metals 150 C, 150 C, slip systems. 50 MPa 2 • Movements of Dislocations with jogs - formation (qf) and Ý = A e [-(qd - *b x)/kT] movement (qm) of vacancies. Self diffusion (qd = qf + qm). qd Mg 135 kJ/mol, q Mg 125 kJ/ mol. • Dislocation Climb - Climb of dislocations over sessile Ý = A e (- qd ) / kT dislocations or precipitates. Vacancy diffusion to and Ý = Be e (-qd ) / kT from edge dislocations (qd) and formation of jogs (qj) . q in the range of qd (135kJ/mol) Activation energy, q = qd + qj •Movement of Dislocation Atmospheres - Diffusion of solute Ý = A  e (- qs ) / kT atoms and the viscous behavior of the solute atmosphere qAl in Mg 143 kJ/mole •Grain Boundary Shear - relative movement of grains, deformation in very narrow region adjacent to the GB, the shear direction lies in the boundary with the max resolved shear stress. Affective at high temperatures, usually when the recovery temperature is achieved. Discontinuous. GBs recover before the grains, softening. Accounts for 30% of the deformation. Grain boundary diffusion: 80 kJ/mol. M. S. Dargusch, G.L.Dunlop, K. Pettersen, Proc of Conf. on Magnesium Alloys and their Applications,” B.L. Mordike and K.U. Kainer, Eds,, Wolsburg, Germany, 1998 pp. 277-282.

2 CREEP BEHAVIOR OF Mg-Al ALLOYS (AZ, AM) CREEP BEHAVIOR OF Mg-Al-RE ALLOYS (AE)

AZ91D -- Activation energy in Ý=Anexp (-Q/RT), 125-175°C, 50 MPa Mg-Al-RE was 30-45 kJmol-1, n=2 • Activation energy 35-40 kJmol-1 self-diffusion of Mg (135 kJmol-1) or • Higher creep resistance diffusion of Al in Mg (143 kJmol-1) or • Stable Al-RE containing phases grain boundary diffusion (80 kJmol-1) AE42 ALLOY • No Mg17Al12 phase but some Al coring Al-RE

Q for discontinuous precipitation of Mg17Al12 = 30 kJ/mol Creep induced Mg17Al12 aids easy grain boundary sliding and migration.

At higher stresses: 95 kJ/mol, n = 5 Activated cross slip Dislocation intersection ?

M. S. Dargusch, G.L.Dunlop, K. Pettersen, Proc of Conf. on Magnesium Alloys and their Applications,” B.L. Mordike and K.U. Kainer, Eds., Wolsburg, Germany, 1998 pp. 277-282. M. S. Dargusch, G.L.Dunlop, K. Pettersen, Proc of Conf. on Magnesium Alloys and their Applications,” B.L. Mordike and K.U. Kainer, Eds,, Wolsburg, Germany, 1998 pp. 277-282.

ALLOY DESIGN FOR CREEP IN Mg DIECASTING ALLOYS Metallurgical Stability in Mg-Al-RE ALLOYS (AE)

GENERAL PRINCIPLES

T (C) Mg Al11RE3 Al 2RE Mg17Al12 AVOID Mg17Al12 As-cast 97.5 1.8 0.8 0.0 creep induced precipitation, e.g. Mg17Al12 25C aging, microstructural instability Sr, Ca, RE

150 C 97.7 1.5 0.8 0.0 STRONG GRAIN BOUNDARIES High temperature surface active solutes Sr, Ca, RE (a) (b) 97.0 1.2 1.3 0.6 175 C 97.0 1.2 1.3 0.6 Second phases (line compounds, Sr, Ca, RE Microstructure of AE42 (a) diecast (b) after 175C exposure coherent particles) Sb, Bi MICROSTRUCTURAL MODIFICATION Sr, Ca, RE Sb, Bi, Sn

Ref : B. R. Powell, V. Rezhets, M.P. Balogh, and R.A. Waldo, “Microstructure and Creep Behavior in AE42 Magnesium Die-Casting Alloy”, Journal of Metals, TMS, August 2002, pp. 34-38

* M. Pekguleryuz, M. Avedesian “Magnesium Alloying-Some Metallurgical Aspects,” Magnesium Alloys and Their Applications, DGM, 1992, pp. 213-220

GRAIN BOUNDRY PINNING RATIONALE FOR ALLOY SYSTEM SELECTION

AL Sr • AVOID COSTLY OR RARE ELEMENTS (Sc, Rare earths, Ag, etc) 4 Space Group: I 4 / mmm • MAINTAIN ALUMINUM FOR GOOD DIE CASTABILITY (5-6%) Body centered tetragonal a = 0.445 nm c = 1.105 nm • USE ALKALINE EARTH ELEMENTS (Ca, Sr) - second phases for grain boundary pinning Mg-5Al-1Sr - solute segregation Mg-5Al-2Sr Mg-Al-Sr Mg-6Al-2Sr SYSTEM • AVOID ELEMENTS THAT CAN ADVERSELY EFFECT CORROSION (Cu, Ni)

• CHOOSE TERNARY SYSTEMS FOR SIMPLICITY & COST AND EASE OF MANUFACTURING

• Mg-Al-Sr SELECTED AS THE OPTIMUM ALLOY SYSTEM TO DEVELOP

3 Mg-Al-Sr ALLOY COMPOSITIONS Microstructure of Diecast AJ Alloys

Alloy designation : AJ Alloys where J designates Sr AJ51x AJ52x AJ62Lx AJ62x Al Sr ALLOY wt. % wt. % -Mg solid solution and a lamellar -Mg and intermetallic ( Type A ) AJ51x 4.5 - 5.5 1.2- 1.5 Type A

Type B AJ52x 4.5 - 5.5 1.6- 2.3 intermetallics A-type AJ62x 5.5 -6.5 2.0- 2.6

AJ62Lx 5.6 -6.6 1.5- 1.9

Sr/Al < 0.3 Sr/Al > 0.3

Mg-Al-Sr Alloy Phases Solidification Curves of AJ51x and AJ52x Mg-Al-Sr Alloy Phases -1..5 Philips X’Pert diffractometer - Cu K radiation AJ51x Using XRD coupled with Liquidus: AJ51x Al4Sr 2500 617-618°C +-Mg AJ52x analytical STEM AJ51x -- DC ) ) s 2000 s -1 / AJ62x, AJ51x: / C C ° 1500 ° r r ( 4 4 ( S

Type-A compound is S r r 4 4 0 0 0 l S 0 l S r 0 4 2 r 0 4 r 2 r l A l 1 A r S 1 4 r S 4 0 S 0 S e 0 e 4 0 1 A S 4 4 1 A 2 S 4 l 2

isomorphous to Al Sr and l r l r l 4 4 2 0 2 l t 0

4 1 0 l

4 t S 1 0 S

1000 A A

1000 A 2 A 2 4 2 4 2 A l A l 1 a 1 a A A

Al/Sr ratio is close to Al Sr r

Al/Sr ratio is close to Al Sr r 2

4 2

4 S S 4 0 4

0 -0.5 l R

l -0.5 R 0 0 A A with some Mg in solution. 500 g g n n i i l 2500 l unknown phase Al4Sr + -Mg ) o ) AJ52x - DC AJ52x - DC o Al Mg Sr s s 3 13 t

AJ52x: o AJ52x: t 2000 o

n 2000 n 533°C Al4Sr C C

u 0 Type-A compound u 0

Type-A compound o AJ52x o 515-518°C c c 1500 ( r corresponds to Al Sr with 15 ( r 4 Al Mg Sr 4 Al Mg Sr S

S r

4 r 3 13

4 3 13 4 0 0 0 l S 0 l S r 0 4 y 2 r 0 4 r y 2 r l A l 1 A 1 S 4 r S 0 S 4 r 0 S t t 4 0 4 1 A 0

wt.% Mg. 4 S

wt.% Mg. 1 A 2 l 4 S 2 l r l r l i 4 i 4 2 0 2 0 1 0 l 1 0 l S

1000 A S A

1000 A 2 A 4 2 4 2 s 2 s l A l A 1 1 A A n n r r 2 2 S S 4 0 4 e 0 e l l 0 0 t A t Type-B compound does not 500 A 0..5 n n I correspond to any known I 625 600 575 550 525 500 475 450 425 crystal. Tentative : 0 625 600 575 550 525 500 475 450 425 3Al.13Mg.Sr 20 25 30 35 40 45 50 55 60 Temperatture (°C) 2q °C)

CREEP DEFORMATION IN AJ52x TYPICAL CONSTANT LOAD CREEP CURVES CREEP DEFORMATION 0.25 50 MPa, 150 C, 500 hours creep samples shows 50 MPa, 150 C very little dislocation pile up, and some sub-grain 0.2 formation

) -4 -4

% = 10 to 10 %/hr

( Ý dislocations ACTIVATION ENERGY * n 0.15 i a r

t 150-175C, 35-100 MPa range S

p 0.1 Q = 32-25 kJ/mol e e r C 0.05 POSSIBLE MECHANISMS 0 Sub-grain formation (stress activated recovery) 0 1000 2000 3000 4000 • • Precipitation induced creep ? (change in relative Time (hours) fractions of phases) • Grain migration ? * E. Landriaut, Ecole Polytechnique, M.Eng. Thesis * E. Landriaut, Ecole Polytechnique, M.Eng Thesis

4 CREEP IN MAGNESIUM DIECASTING ALLOYS PERFORMANCE REQUIREMENTS FOR DIECASTING ALLOYS Creep resistance (tensile & compressive) up to 175°C (min creep rate) Failed after 80 hours TENSILE CREEP  °C (min creep rate) COMPRESSIVE CREEP P P E 10  Bolt-load retention up to 175°C (50% min) E E 25 E R 50 MPa, 150C, 200 hr R de./ dt C C

70 MPa, 150C, 200 h Metallurgical / thermal stability % 9 50 MPa, 175C, 200 hr  % Tensile yield strength up to 175 100 MPa) TIME 8 70 MPa, 175C, 200 hr  °C ( N N 20 N N O O O O

I Fatigue resistance (fatigue limit at 175 C : 45 MPa min) I Fatigue resistance (fatigue limit at 175 C : 45 MPa min) I I S  ° S YS

T S YS UTS

T 7 S UTS T T E E A A A A R R

Ultimate tensile strength up to 175 130 MPa) T Ultimate tensile strength up to 175 130 MPa) T M M °C (

M  °C ( M  S 6 S R R R R 15 AUTOMATIC 2 STRAIN O O O O  Salt-spray corrosion resistance (0.1-0.25 mg/cm /day) F F F 5 F TRANSMISSION E E E E CASE D D D D Elongation (min 3% at room temperature)

 P P P 4 P 10 E E E E ENGINE-BLOCK Acceptable diecastability (comparable to AM or AE) E E 

E   E  R R R 3 R C C C C Acceptable cost (5-10 over alloy prices)

 ¢ % % % 2 % 5 Availability of raw materials 1 Alloy production (compatibility with plant processes) 0 0 0

3 Melt handling (oxidation, sludge formation) 1 2 0 x D 3  2 2 5 L 4 8 4 1 2 1 AZ91D AS41 AS21x AE42 AJ62x AJ52x A380 1 6 5

2 3 2 I S E 9 I J J

6 AXJ531 S R A Z

A Recyclability A Recyclability R AJ62L J A A MRI 153  A M A

M MRI 230 A AJX500

YIELD STRENGTH ULTIMATE TENSILE STRENGTH 300 20 C A380 AJ62L 20 C AXJ531 200 150 C 150 C 175 C 175 C MRI230 AXJ531 AJ62 A380 MRI153 ACM522 AZ91 AJX500 a a MRI230 ZAX850

P MRI230 ZAX850 P AJ62L MRI153 AJ52 AE42 M M ACM522 AJ62 AS21x

AZ91 , , AS41 S S AJX500 AJ52 S S ZAX850 ZAX850 AE42 200 E E a AS41 a R R P AS21x P T T M M

S S , , S S S S E E R 100 R T T S S 130

100

0 ALLOY 0 ALLOY

OTHER PROPERTIES OF AJ ALLOYS CORROSION PROPERTIES OF MAGNESIUM DIECASTING ALLOYS

120 High thermal conductivity : AJ52 • 100 x 75-95 W/m K, 22-450 C (AZ91D : 58-78 W/m K) y = -5.5364Ln(x) + 110.49 R2 = 0.636 )

a 80 P M (

s s

e 60

r y = -4.8445 Ln(x) + 97.35 t CORROSION RATE S R2 = 0.6999 High fatigue resistance

• d ALLOY e i

l 40 2 at elevated temperature p (mg/cm /day) p

A 150 C 22 C 20 Broke --150 c Stopped -- 22C Stopped -- 150C Broke -- 22 C AZ91D 0.10 Not used in equation Good fracture toughness 0 • Good fracture toughness 10 100 1000 10000 100000 AE42 0.21 Cycles x 1000 120 AE42 y = -2.6044 Ln(x) + 108.42 AS41 0.16 R2 = 0.5066 100 AJ62x 0.11 Fluxless Recycling ) AJ62x 0.11 • Fluxless Recycling a P 80 AJ52x 0.09 M (

s s

e 60 AJ62Lx 0.04 r • Compatible with t

S y = -7.6106 Ln(x) + 112.64

most cover gases d 40 R2 = 0.9097 MRI 153 0.09 e i l p

p 150C 22C 20 MRI 230 0.10 A Broke --150 c Stopped -- 22C Stopped -- 150C Broke -- 22 C 0 A380 0.34 10 100 1000 10000 100000 Cycles x 1000

5 CASTABILITY IMPROVEMENT CASTABIILIITY IIMPROVEMENT Fraction Solid Evolution

AVERAGE ALLOY AZ91D HOT TEAR RATING* A380 2 AZ91D 20 AZ91E 14 AM50A 44 AM60A 31 ITM alloy (0.8%Ca) 61 AJ50x (0.2Ca, 0.5Sr) 45-60 AS21 69 AS21x 27 Mg-Al-Ca AS41B 82 AE42 95 AJ51x 35-50 AJ52x 24 AJ53x 5 AJ62x 2 AJ62Lx 0 *A lower number means AJ52x AJ62x AJ62Lx less susceptibility to hot tearing H = 450 J/kg H = 500 J/kg H = 530 J/kg

DIIECASTABIILIITY OF AJ ALLOYS BMW ENGINE BLOCK

ALLOY Die Sticking Cracking Fluidity Overall Rating • First commercialization of a Mg alloy in engine applications

AJ52x low Low Good Good. If recommended Hybrid engine block with parameters are used • Al-Si hypereutectic alloy very good castability Al insert and Mg block can be obtained. Similar 10,000 MT of annual usage AJ62x Very low none Very good • to AM Similar • BMW has 3 years of AJ62Lx Very low none Excellent AJ62Lx to AM AZ exclusive rights to the AJ alloy patent for use in engine applications

Mg-Al-Sr (AJ) alloy

FUTURE WORK IN Mg ALLOYS AUTOMOTIVE USES OF MAGNESIUM Creep Resistant Alloys CURRENT USE: INTERIOR MID-TO-LONG-TERM Investigate creep mechanisms in new alloys COMPONENTS BODY Investigate microstructural evolution during creep e.g. I P, steering wheel Creep design for higher temperatures - Yield strength e.g Inner door panel, pillar structures - Energy absorption - Wrought products (formability) Castability research on existing alloys - existing alloys (AM alloys) - Structural casting alloys (ductility) - Requires new alloys and processes High Ductility Alloys Improved ductility of the primary phase with solute additions AJ62Lx Improved ductility of the primary phase with solute additions Modified AJ62Lx type alloys

Mg Wrought Alloys CHASSIS e.g. Wheel, suspension arm Understanding texture, formability, recovery, microstructure effects in existing alloys - Strength Alloy modification as it relates to recovery and formability SHORT TERM : ENGINE & - High ductility The role of trace elements TRANSMISSION - Corrosion resistance Low Li (2%) with trace elements e.g. Transmission case, engine parts AJ52 - Requires new alloys The role of Mn - Creep resistance AJ62 - Stiffness Effect of solutes - Corrosion resistance Grain refining and prevention of grain growth with trace elements - AE, AS alloys Modify surface texture for bending - Requires new alloys - Potential use 60 000tp y Understanding twin roll casting, rolling, bending operations

6 Partial Castability Index MARKET GROWTH $ 1.5 US / lb $ 1.0-1.2 US / lb 160 Aluminum alloying Castability index for thin walled parts: 0.1( F ) + 0.4 + 0.3 HTS + 0.2 T’     140

) Magnesium diecasting Castability index for medium walled parts : 0.1(F) + 0. 2) + 0.4 HTS +0.2’’ T 120 M

( 100

Steel desulfurization Castability index for thick-walled castings : 0.2(F) + 0. 3 + 0.4 HTS -+0.2’ E Z I 80 S

E 60 K R where, F = (freezing range for AZ91) – (freezing range for alloy) A 40 where, F = (freezing range for AZ91) – (freezing range for alloy) M 20 = (thermal conductivity of alloy) – (thermal conductivity of AZ91)   = (thermal conductivity of alloy) – (thermal conductivity of AZ91) 0 1995 1997 1999 2001 2002 HTS = (Hot-tear sensitivity of AZ91) – (hot-tear sensitivity of alloy) Highest market growth potential is in ’ = (near equilibrium freezing-range of alloy) – (60 C)   magnesium diecasting alloys used in automotive and electronics applications (6-9%)

TENSILE CREEP IN AJ & OTHER Mg ALLOYS

% Creep % Creep % Creep COMPRESSIVE CREEP IN AJ & OTHER Mg ALLOYS @ 50 MPa, 200 hrs @ 50 MPa, 500 hrs @ 70 MPa, 200 hrs (Ref) ALLOY 150 C 175 C 150 C 175 C 175 C % COMPRESSIVE CREEP % BOLT LOAD RETENTION AJ52x 0.04 0.05 0.03 0.09 0.14 70 MPa, 100 hours (Ref) ALLOY @ 150C, 70 MPa, 200 hrs AJ62x 0.05 0.05 - - - 150 C 175C

AJ62Lx 0.13 0.29 - - - AJ52x 0.24 73% 49% AE42 0.06 0.33 0.08 0.18 0.44 AJ62x 1.73 - - AS41 0.05 2.48 0.07 - - AE42 2.16 65% 50% AS41 AS21x 0.19 1.27 - - 8.95 6.13 - - AS21x 3.97 55% 29% AZ91D 2.7 * 6.35 - - AZ91D 21 - - A380 0.08 0.04 0.10 0.05 0.22** A380 0.03 - 81% * *failed after 80 hrs **A383 alloy *A383 alloy Ref : A. P. Druschitz, E. R. Showalter, J.B. McNeill, D. L. White, “Evaluation of Structural and High-Temperature Magnesium Alloys”, SAE Paper 2002-01-0080. Ref : A. P. Druschitz, E. R. Showalter, J.B. McNeill, D. L. White, “Evaluation of Structural and High-Temperature Magnesium Alloys”, SAE Paper 2002-01-0080.

DESIGN PRINCIPLES FOR CREEP-RESISTANT ALLOYS AJ62Lx Microstructure 1. MINIMIZE RECOVERY AND SOFTENING EFFECTS;

•SOLID-SOLUTION HARDENING T=0.3Tm AJ62Lx Element Solid-solubility limit (wt%) Melting point, °C

Zinc 2% at 20-150°C and 6.2% at 325°C 420 Aluminum 2 % at 20°C; 3% at 200°C and 12.6 % at 437°C 660 Rare Earths (Ce) Negligible at 20°C and 0.15 % at 337°C 798 Al4Sr Calcium Negligible at 20°C and 0.5% at 250°C 840 Copper No solid solubility of Cu in Mg 1085 Manganese Negligible at 20°C and 0.1 % below 300°C 1246 Silicon No solid solubility of Si in Mg 1414 Yttrium 1.8-2% at 200°C and 6.5% at 566°C 1528 Al12Mg17 Zirconium 0.2% at 300°C and 3.5% at 654°C 1865

• PRECIPITATION HARDENING DEPENDS ON HEAT-TREATMENT AND CANNOT BE APPLIED TO DIECAST MATERIALS DUE TO BLISTERING

7 CHARACTERISTICS OF SECOND PHASES IN Mg DIECASTING ALLOYS Mg-Al-Ca ALLOYS (AX)

ALLOY SECOND PHASES CREEP Mg-5Al-0.6Ca Mg-5Al-0.8Ca 3000 MELTING CREEP INDUCED RESISTANCE 3000

PHASE TYPE POINT PRECIPITATION 2400 Al 2Ca 2400 Al2Ca

Mg2Ca 1800 1800 Mg-Al (AM) Mg17Al12 42- 58% Al 437°C Mg17Al12 (eutectoid) Low Mg-Al-Zn (AZ91) Incoherent with -Mg Mg-Al-Zn  / 1200 1200 SE C

C E S

Mg Al See above 600 Mg-Al-Si Mg Al See above / 17 12 NT 600 Mg Al (eutectoid) Borderline S 17 12 ) S T Mg Si Line compound** 1085°C N 2 C 0 0 15 25 35 45 15 25 35 45 55 65 75 Mg-Al-RE (AE42) Al2RE Mg17Al12 and Line compounds** 1480°C Good 55 65 27 T5HETA 2 THETA Al11RE3 Al2RE (above 150 °C)

Mg-Al-Ca Al2Ca Line compound ** 1079°C - Good ) ) % % AZ91D ( (

Al RE, Al RE Line compounds** 1480°C N Al2RE, Al11RE3 Line compounds** 1480°C N O O I I S Mg-Al-RE-C a - M n Al2Ca Line compound** 1079°C - Good S N N E E T Mn-Al-RE & Al-Ca-RE Intermetallics (Al-Mn-Ce) and/or T X X E E

Al-Mn-La intermetallics 6 P P 2 1 0 8 5 E 4 E 5 0 E X 5 E

E X A A A X R Al Sr and Al-Mg-Sr AX51 R Mg-Al-Sr Al4Sr and Al-Mg-Sr 1040°C - Good A C permanent- C AX51 diecast mold cast **(Laves phase)

ALLOYS DEVELOPED IN 1992-2002 MICROSTRUCTURES OF RARE-EARTH & CALCIUM ALLOY DESIGNATION INVENTOR STATUS / COMMENTS CONTAINING (NISSAN, HONDA, DSM) ALLOYS Mg-Al-Si AS41 (Mg-4Al-1Si) VW Commercial AS21 (Mg-2Al-1Si) ACM522 (Mg-5Al-2Ca-2RE) MRI 153 i Mg-Al-Si (RE) AS21x Hydro Mag. PATENTED

Mg-Al-RE AE42 (Mg-4Al-2 RE) Dow Commercial

Mg-Al-Ca AX51 {Mg-5Al-(.2-.8)Ca} ITM WO96/25529 (1995), PD* high melting-point Mg-Al-RE-Ca AEX Nissan-UBE EP 0799901 A1 (1997) NK** second phases ii ACM522--(Mg-5Al-2RE-2Ca) Honda EP 0791 662A1 (NK**) Mg-RE-Ca (Mn) EX {Mg-(2-5)RE-(0-1)Ca} MEL WO96/24701 (NK**) Al-(RE, Ca) compounds Mg-Zn-Al-Ca ZAX850 IMRA US 5855697 (1999) Interaction of stable Mg-Al-RE-Ca (Sr) MRI 153, MRI 230D DSM-VW US 6139651 (2000) phases with dislocations HONDA PATENT Mg-8%Al-2.5%RE-1.6%Ca-1.3%Mn Mg-Al-Sr AJ {Mg-(2-9)Al-(.5-7)Sr} Noranda US 6322644 (2001) and grain-boundary permanent-mold cast Mg-Al-Ca-Sr AXJ {Mg-5Al-(2-3)Ca-0.07Sr GM US 6264763 (2001) pinning Al2Ca lamellar phase, needle shaped Mg-Al-Sr-Ca AJX {Mg-(2-9)Al-(.2-.6)Sr-(.15-.3Ca) Noranda US 6342180 (2002) Al-RE (Ca, Mn) and Al-Mn-RE intermetallics * PD: public domain ** NK: status not known

TENSILE PROPERTIES OF AJ & OTHER Mg ALLOYS CREEP IN AJ & OTHER Mg ALLOYS ALLOY PROPERTY A380 AJ62x AJ52x AJ62Lx AE42 AS41 AS21x* AZ91D Failed after 80 hours TENSILE CREEP COMPRESSIVE CREEP YIELD STRENGTH (MPa) 10 50 MPa, 150C, 200 hr 25 20 C 155 (180) 143 134 152 128(145) 136 (140) 121 139 (160) 70 MPa, 150C, 200 h 9 50 MPa, 175C, 200 hr N 150 C 154 (159) 108 110 116 88 (100) 94 (95) 87 105 (108) N N 8 70 MPa, 175C, 200 hr N

O 20 O O I O I I I T T T 175 C 148 (148) 103 100 109 81 (91) 85 (85) 78 89 T A A 7 A A M M M ULTIMATE TENSILE STRENGTH (MPa) M R R 6 R

R 15 O O O O F 20 C 290 (290) 240 212 276 220 (230) 197 (215) 210 204 (240) F

20 C 290 (290) 240 212 276 220 (230) 197 (215) 210 204 (240) F 5 F E E E E D D D D 150 C 251 (257) 163 163 166 140 (157) 153 (155) 130 169 (157)

4 10 P P P P E E E 175 C 248 (228) 143 141 143 121 (130) 127 (127) 110 138 E E E E 3 E R R R R C C C C ELONGATION (%)

2 5 % % % % 20 C 3.2 (3) 7 6 12 10 (11) 4 (6) 5.5 3.1 (3) 1 150 C 6.4 (7) 19 12 27 23 (20) 17 (24) 20 16 (23) 0 0 1 x 2 x x 0 x D R 1 4 4 2 2 8

1 L AZ91D AS41 AS21x AE42 AJ62x AJ52x A380 E 2 6 5 3 S 175 C 7.1 (10) 19 18 27 23 (23) 19 (25) 23 21 9 E 2 J J H S 6 Z A A A T J A A A A O *Ref : A. P. Druschitz, E. R. Showalter, J.B. McNeill, D. L. White, A Structural “Evaluation of and High-Temperature Magnesium Alloys”, SAE Paper 2002-01-0080

8 PERFORMANCE OF NEW CASTING ALLOYS

COMPRESSIVE CREEP BOLT LOAD RETENTION 25 100 70 MPa, 150C, 200 h 70 MPa, 150C, 100 hr 90 70 MPa, 175C, 100 hr D D N N E 20 E 80 O O I N I N I DEVELOPMENT OF I T T A A

A 70 A T MAGNESIUM-ALUMINUM-STRONTIUM ALLOYS T M

MAGNESIUM-ALUMINUM-STRONTIUM ALLOYS M E E R R R R

15 60 O O H H F F T T E E 50 G G D D

N N P P E 10 E 40 E E R R E E T T R R S S

30 C C T T L L % % O 5 O 20 B B

% % 10 0 0 AZ91D AS41 AS21x AE42 AJ62x AJ52x A380 OTHER AS21x AE42 AJ52x A380

Ref : A. P. Druschitz, E. R. Showalter, J.B. McNeill, D. L. White, “Evaluation of Structural and High-Temperature Magnesium Alloys”, SAE Paper 2002-01-0080.

CREEP DEFORMATIION CREEP BEHAVIOR OF Mg-Al-Si ALLOYS (AS)

LOW-TO-MODERATE TEMPERATURES Stress-Activated Recovery : grain sub-structures. HCP elongated (R.T), AS21 ALLOY CREEP BEHAVIOR IS SIMILAR TO Mg-Al ALLOYS Al : equiaxed (150C)

• Activation energy 35-40 kJmol-1 n Ý = A  e (-Q/RT) HIGH TEMPERATURES • Involvement of the Mg17Al12 second phase Thermally Activated Recovery Dislocation Creep dislocation intersection, dislocation climb, movement of dislocation atmospheres, • Slight improvement over cross-slip, grain-boundary shear. AZ and AM alloys.

Ý = B e (-Q/RT) Ý  Smaller amount of the Mg17Al12 Diffusion-Creep: fast diffusion paths and some grain boundary (dislocation cores or GB) or pinning from Mg2Si phase bulk diffusion (vacancy and interstitial) (qd or qs)

T> 0.3 Tm M. S. Dargusch, G.L.Dunlop, K. Pettersen, Proc of Conf. on Magnesium Alloys and their Applications,” B.L. Mordike and K.U. Kainer, Eds,, Wolsburg, Germany, 1998 pp. 277-282.

Solidification Curves of AJ52x and AJ62x Alloys

Al3Mg13Sr Al-Si hypereutectic alloy -0.75 AJ62x Sr/Al > 0.3 AJ62x -0.65

) AJ52x s /

C -0.55 Al4Sr + (-Mg) Al Sr + -Mg ° 4  (

t -0.45

a AJ52x

R Al- Mg- Sr -0.35 , , Mg-Al-Sr (AJ) alloy g n i l

o -0.25

o Liquidus C -0.15 610-615°C Al Mg Sr Al4Sr 3 13 516 -0.05 520-530°C °C

625 600 575 550 525 500 475 450 425 Temperature (°C)

9 MECHANISMS OF CREEP PURE MAGNESIUM(90-300°C, 8-70 MPa)* LOW TEMPERATURES : basal slip, twinning and sub-grain formation, (transient creep)

Principal twin plane

Pyramidal planes (2nd order) Basal planes

HIGHER TEMPERATURES: non-basal slip, twinning grain boundary deformation and sliding (steady-state creep) Q= 65 kJ/mol

Pyramidal planes (first order)

* G.V. Raynor, The Physical Metallurgy of Magnesium and Its Alloys, Pergamon Press, Oxford, UK, 1959, pp. 247-249, 348.