Options for yield strength Options for yield strength enhancement of Alenhancement of Al--stabilisedstabilised

1st Linear Collider Detector (ILC/CLIC) Magnet Workshop

enhancement of Alenhancement of Al--stabilisedstabilisedsuperconductorssuperconductors

S. Sgobba

CERN, CH-1211 Geneva

• The present CMS conductor:

□ materials and developments□ state of stress, safety factors

• Toward an improved conductor

reinforcement alloy EN AW-6082 or EN AW-7020?

Outline of the talkOutline of the talk

□ reinforcement alloy EN AW-6082 or EN AW-7020? □ replacement of pure Al stabilizer by cold drawn Al-0.1wt%Ni□ weldability

• Comparison of mechanical properties and equivalent RRR of the improved conductor

• Limits and perspective of alternative solutions for yield strength enhancement

The present CMS conductor,The present CMS conductor,materials and geometrymaterials and geometry

Insert ReinforcementReinforcement

Al 99.998 % stabilizer

32 strands Rutherford typesuperconducting cable

⇐ EN AW-6082 T6 continuous extrusions ⇒

Nominal current 20 kAInsert ReinforcementReinforcement Nominal current 20 kASuperconducting strand type NbTi- Cu stabilized

Strand Cu/SC ratio 1.1

Number of strands 32

Strand diameter 1.28 mm

Rutherford cable cross section 20.68 mm x 2.34 mm

Insert cross section 30 mm x 21.6 mm

High Purity Aluminum stabilizer Al 99.998 %

RRR aluminum at 0 T, annealed > 1500

Reinforcement material EN AW-6082

Conductor cross section 64 mm x 21.6 mm

Quantity produced 21 lengths x 2600 m

The present CMS conductor,The present CMS conductor,billet on billet extrusion of the reinforcementbillet on billet extrusion of the reinforcement

Schematic representation of the extrusion line (S. Sequeira Tavares, S. Sgobba, An improved billet on billet extrusion process of continuous aluminium alloy shapes for cryogenic applications in the Compact Muon Solenoid experiment, J. of Mat. Proc. Technology 143–144 (2003) 584–590)

The present CMS conductor,The present CMS conductor,EB weldingEB welding

Electron Beam (EB) welding seams

The present CMS conductor,The present CMS conductor,curing cyclecuring cycle

The present CMS conductor,The present CMS conductor,tensile and electrical propertiestensile and electrical properties

B. Curé et al., “Mechanical Properties of the CMS Conductor”, IEEE Trans. Appl. Superconduc., vol. 14, no. 2, pp. 530-533, June 2004

Toward an improved conductor,Toward an improved conductor,material selectionmaterial selection

Replace by:

o a higher strength Al-alloyo extrudableo weldableo compatible with a cryogenic

applicationo maintaining high ductility and o maintaining high ductility and

strength at 4.2 Ko even after a curing cycle

Replace by:

o cold drawn Al-0.1wt%Ni alloyo developed for the ATLAS thin solenoid superconductor (A. Yamamoto et al., Development towards Ultra-thin Superconducting Solenoid Magnet for High Energy Particle Detectors, Nuclear Physics B (Proc. Suppl.) 78 (1999), pp.565-570) o enhanced mechanical strength o without excessive degradation in RRR compared to pure Al

Toward an improved conductor,Toward an improved conductor,reinforcementreinforcement

Extrudable,weldable

Candidate alloy:

o EN AW-7020 (Al-Zn4.5Mg1 alloy), equivalent of EN AW-7005o Extrudable and weldable

Toward an improved conductor,Toward an improved conductor,reinforcementreinforcement

o High ductility and strength at 4.2 K even after curing?

o Sections of 18±0.4 mm x 24±0.4 mm supplied byOtto Fuchs /DE

o Lengths of 3 m to 6 mo Two different T6-type tempers (designation .71 and .72

according to DIN 17007)

0

100

200

300

400

500

600

700

800

900

Rp0.2 Rm A

Rp

0.2

/MP

a, R

m /M

Pa,

A ×

1000

.71 temper, as received

.72 temper, as received

.71 temper, cured

.72 temper, cured

RT

EN AW-6082 T6 (cured)

EN AW-6082 T51EN AW-6082 T6 (cured)

Rp0.2 Rm A

0

100

200

300

400

500

600

700

800

900

Rp0.2 Rm A

Rp

0.2

/MP

a, R

m /M

Pa,

A ×

1000 4.2 K

EN AW-6082 T6 (cured)

EN AW-7020.72, cured, at 4.2 K

Rp0.2 = 677 MPa Rm = 817 MPa

EN AW-7020.72, cured, at RT

3.1cured)-as T61 6082AW (EN

cured)-as .72 7020AW (EN

2.0

2.0

=p

p

R

R

EN AW-7020.72, cured, at 4.2 K

6.1cured)-as T61 6082AW (EN

cured)-as .72 7020AW (EN

2.0

2.0

=p

p

R

R

EN AW-7020.72, cured, at RT and 4.2 K

Toward an improved conductor,Toward an improved conductor,safety factorssafety factors

2.1cured)-as T61 6082AW (EN

cured)-as .72 7020AW (EN=

m

m

R

R

Safety factors:

EN AW-7020.72 ⇒ 3 (677 MPa/225 MPa)EN AW-6082 T61 ⇒ 1.9 (428 MPa/225 MPa)

with respect to the actual 4 T design strength at 4.2 K

From 4 T to 6 T:

Toward an improved conductor,Toward an improved conductor,safety factorssafety factors

From 4 T to 5 T:

“It seems difficult, respecting construction codes, to exceed a hoop strain of 0.15%. In the case of CMS, this corresponds to a maximum Von Mises stress of 140 MPa, requiring alloys with Rp0.2 > 210 MPa and Rm > 420 MPa at 4.2 K. Thus one can tentatively conclude that the

225 MPa ⇒⇒⇒⇒ 506 MPa

EN AW-7020.72 ⇒ 1.3 (677 MPa/506 MPa)EN AW-6082 T61 ⇒ 0.84 (428 MPa/506 MPa)

with respect to a design strength at 4.2 K (ceteris paribus)

225 MPa ⇒⇒⇒⇒ 350 MPa

EN AW-7020.72 ⇒ 1.92 (677 MPa/350 MPa)EN AW-6082 T61 ⇒ 1.22 (428 MPa/350 MPa)

with respect to a design strength at 4.2 K (ceteris paribus)

Thus one can tentatively conclude that the selected alloys EN AW-6082-T51 for the reinforcement and EN AW-5083-H321 for the mandrels are perfectly suitable for a 5-T coil”

A. Hervé et al., Experience Gained from the Construction, Test and Operation of the Large 4-T CMS Coil, paper presented at MT20 (2007)

Candidate alloy:

v Al99.998 ⇒ Al-0.1wt%Ni v developed for the ATLAS thin

solenoid superconductorv aiming an Rp0.2 = 85 MPa at

4.2 K after curing

Toward an improved conductor,Toward an improved conductor,stabilizerstabilizer

A. Yamamoto et al., Nuclear Physics B 78 (1999), pp. 565-570;Wada et al., IEEE Trans. Appl. Superconduc., vol. 10, pp. 373-376, March 2000

v Al-0.1wt%Ni is a work-hardenable alloy

v softens only partially with curing cycles

v compromise strength/RRR

ATLAS coil curing: ATLAS coil curing: 130 130 °°CC--15 h15 h

Effect of CMS coil Effect of CMS coil curing (including a curing (including a 135 135 °°CC--50 h 50 h plateau)?plateau)?

AlAl--0.1wt%Ni0.1wt%Ni

Toward an improved conductor,Toward an improved conductor,stabilizerstabilizer

AlAl--0.1wt%Ni, from K. Wada et al., IEEE Trans. Appl. 0.1wt%Ni, from K. Wada et al., IEEE Trans. Appl. Superconduc., vol. 10, pp. 1012Superconduc., vol. 10, pp. 1012--1015, March 20001015, March 2000

plateau)?plateau)?

200

250

300

350

400

Rp

0.2

/MP

a, R

m /M

Pa,

A /%

RT, as drawnRT, cured4.2 K, as drawn4.2 K, cured

20 % to 23 % typical reduction in area

Toward an improved conductor,Toward an improved conductor,stabilizerstabilizer

0

50

100

150

200

Rp0.2 Rm A

Rp

0.2

/MP

a, R

m /M

Pa,

A /%

AlAl--0.1wt%Ni, CMS0.1wt%Ni, CMS--type curing, at 4.2type curing, at 4.2 K: Rp0.2 = 82K: Rp0.2 = 82±±7 MPa7 MPa

Four roll shaping processFour roll shaping process(courtesy of Outokumpu /IT)(courtesy of Outokumpu /IT)

allowed 11.3 % reduction in area

Toward an improved conductor,Toward an improved conductor,stabilizerstabilizer

30

40

50

60

Str

eng

th /M

Pa;

Har

dn

ess

As received

After roll shaping

EN AW 1199 Aluminum

0

20

40

60

80

100

120

140

0 20 40 60 80

Reduction by cold rolling /%

Str

eng

th /M

Pa,

Elo

ng

atio

n /%

Tensile strength /MPa

Yield strength /MPa

Elongation /%

Toward an improved conductor,Toward an improved conductor,stabilizerstabilizer

0

10

20

30

Yield strength/MPa

Tensile strength/MPa

Hardness /HBS

Str

eng

th /M

Pa;

Har

dn

ess

Toward an improved conductor,Toward an improved conductor,global tensile properties of a rollglobal tensile properties of a roll--shaped insertshaped insert

Global and local tests, a comparison

100

120

140

Str

eng

th /M

Pa;

elo

ng

atio

n /%

Yield Strength /MPaUltimate Tensile Strength /MPaElongation /%

0

20

40

60

80

As received Roll shaped, test 1 Roll shaped, test 2

Str

eng

th /M

Pa;

elo

ng

atio

n /%

Toward an improved conductor,Toward an improved conductor,weldabilityweldability

Al-0.1wt%Ni EN AW-7020

acc. /kV =120intensity /mA =9.26cath. curr /A =1.35working distance /mm =150 adv. speed /mm·s-1 =16.7X,Y scanning

Comparison of properties,Comparison of properties,basis for a comparison of 4.2 K propertiesbasis for a comparison of 4.2 K properties

70207020 SSSS AlNiinsertAlNiinserti

iicc σσσσ +==∑

Equivalent stress σc acting on the improved full conductor:

σAlNiinsert = stress in the insertσAlNiinsertσ7020 = stress in the reinforcementSAlNiinsert = cross sectional area of the insertS7020 = cross sectional area of the reinforcement

Contribution of the Rutherford to the yield neglected (conservative in the case of roll shaped inserts)

Comparison of properties,Comparison of properties,basis for a comparison of 4.2 K propertiesbasis for a comparison of 4.2 K properties

706 MPa600

700

800

900

1000

stre

ss /M

Pa

EN AW-7020.72 as cured, sample 10

Al-0.1wt%Ni as cured, sample 4

weighted average

104 MPa0

100

200

300

400

500

0 0.005 0.01 0.015

strain

stre

ss /M

Pa

424 MPa

Comparison of properties,Comparison of properties,basis for a comparison of 4.2 K propertiesbasis for a comparison of 4.2 K properties

At 4.2 K, as CMS-cured state:

Minimum yield strength of the full conductor, evaluated at the 0.2% yield point of the reinforcement,

•for EN AW-7020.72 + Al-0.1wt%Ni = 400 MPa•for EN AW-6082 (T6) + Al99.998 = 258 MPa [1]

Equivalent RRR = 420 (RRR of the as-cured Al 0.1wt%Ni = 900 x cross sectional ratio of the insert [1])

[1] B. Curé et al., “Mechanical Properties of the CMS Conductor”, IEEE Trans. Appl. Superconduc., vol. 14, no. 2, pp. 530-533, June 2004

Comparison of properties,Comparison of properties,basis for a comparison of 4.2 K propertiesbasis for a comparison of 4.2 K properties

200

250

300

350

400

Rp

0.2

/MP

a, R

m /M

Pa,

A /%

RT, as drawnRT, cured4.2 K, as drawn4.2 K, cured

0

50

100

150

200

Rp0.2 Rm A

Rp

0.2

/MP

a, R

m /M

Pa,

A /%

AlAl--0.1wt%Ni, CMS0.1wt%Ni, CMS--type curing, at RT: Rp0.2 = 59type curing, at RT: Rp0.2 = 59±±2 MPa2 MPa⇒⇒⇒⇒⇒⇒⇒⇒ RRR RRR ≈≈ 900900

Progress of Al-stabilized SC

A. Yamamoto, “Advances in Superconducting Magnets for Particle Physics”, IEEE Trans. Appl. Superconduc., vol. 14, no. 2, pp. 477-484, June 2004.

Comparison of properties,Comparison of properties,basis for a comparison of 4.2 K propertiesbasis for a comparison of 4.2 K properties

ATLAS CS

Bess PCMS

Improved CMS

150200250300350400450500

Eq

uiv

alen

t yi

eld

str

eng

th /M

Pa

ATLAS CS

050

100150

0 400 800 1200 1600

RRR

Eq

uiv

alen

t yi

eld

str

eng

th /M

Pa

Composite AlComposite Al--based pure metal based pure metal conductorsconductors

High purity aluminum composite conductors with Al-alloy matrix developed in the 90ies

o C.E. Oberly and J.C. Ho (Wright Res. & Dev. Center, Wright-Patterson AFB, OH), The origin and future of composite aluminium conductors, Magnetics, IEEE Transactions on, 27 (1991) 458-463

o K.T. Hartwig and R.J. DeFrese, Mechanical and Electrical Testing of Aluminum Cryoconductors, Adv. Cryo. Engr., 36A (1990) 709-715

o M. K. Premkumar, , F. R. Billman, D. J. Chakrabarti, R. K. Dawless, A. R. Austen, Composite aluminum

5N Al, RRR=1500 Al-Fe-Ce from PM, VHP

Typical properties at 20 K:YS ≥ 165 MPaUTS ≥ 276 MPao M. K. Premkumar, , F. R. Billman, D. J. Chakrabarti, R. K. Dawless, A. R. Austen, Composite aluminum

conductor for high current density applications at cryogenic temperatures, Advances in cryogenic engineering – Materials, 36 (1990) 733-740

o J. C. Ho, C. E. Oberly, H. L. Gegel, W. M. Griffith, J. T. Morgan, A new aluminum-base alloy with potential cryogenic applications, Advances in cryogenic engineering – Materials, 32 (1986) 437-442

UTS ≥ 276 MPa1.5 % ≤ A ≤ 8 %

Composite AlComposite Al--based pure metal based pure metal conductorsconductors

Limiting mechanical strain of 0.1 % to 0.2 %

350 MPa, RRR 400 to 500in magnetic fields up to 10 T

Current densities not cited: "couldcarry much higher current densitiesthan the practical 2·108 A/m2 of lightweight SC"

AlAl--stabilisedstabilised NbTiNbTi multifilament SCmultifilament SC

o M. Young, E. Gregory, E. Adam and W. Marancik, Fabrication and Properties of an aluminum-stabilized NbTi Multifilament Superconductor

o S. Murase, , Y. Koike, Y. Nakayama, T. Toyoda, E. Suzuki, K. Mendelssohn, Aluminum stabilized Nb--Ti superconducting wires, Proceedings of the fifth international cryogenic engineering conference, Kyoto, Japan, 7 May 1974, IPC Science and Technology Press Ltd., Guildford, Eng. (1974)

Embedding in EN AW-1100 or EN AW-6061 (EN AW-5052 reported)

High purity Al "tube", RRR = 1700

RRR = 320Critical currentdensity at 5 T = 1630 A/mm2

AlAl--stabilisedstabilised NbNb33Sn multifilament SCSn multifilament SC

M. Thöner, H. Krauth, J. Rudolf, A. Szulczyk, Aluminium Stabilized Nb3Sn Superconductors, Adv. Cryog. Eng. Mat. 34 (1988) 507

Reacted "monolith" (80000 filaments in a CuSn matrix)

High purity Al (RRR = 2500 to 5000)

Duratherm reinforcement

Al added after the reaction treatmentSimultaneous extrusion with reactedNb3SnLength up to 100 m (limited by lengthof reacted Nb3Sn)RRR = 580 for the "80000" versionYS = 186 MPa at RT, idem

Duratherm reinforcement(Co-Ni-Cr alloy)

AluminiumAluminium alloy DSalloy DS--AlAl--550550

High temperature compression strength(according to Hellum and Luton, proc. ESA Symp. 1990)

100

200

300

400

500

600

0.2%

pro

of s

tres

s /M

Pa 3% Alumina

7% Alumina

15% Alumina

Mechanical properties at 4.2 Kafter a 10 h thermal treatment

600

700

800None

150 °C-10h

250 °C-10h

•S. SGOBBA, G. MARTIN and T. KURTYKA: Mechanical Properties of a New Dispersion Strengthened Aluminium Alloy for Use at Very Low Temperatures, Proceedings of the 5th European Conference on Advanced Materials, Processes and Applications, Maastricht 21-23 April 1997, vol. 1, p. 251-254

0

0 100 200 300 400 500

T / °C

0

100

200

300

400

500

600

E /GPa Yield stress /MPa UTS /MPa elongation at breakx 10 /%

250 °C-10h

350 °C-10h

••Aluminium alloy DSAluminium alloy DS--AlAl--550550Particle size, 2 nm to 10 nmParticle spacing, 80 nmExpected RRR, less than 10

ConclusionsConclusions

Toward a High Strength, High RRR Conductor:Toward a High Strength, High RRR Conductor:

⇒⇒ Selection of high performance, Selection of high performance, extrudableextrudable reinforcement and insert reinforcement and insert alloysalloys

⇒⇒ PotentialPotential suitabilitysuitability of the of the alloysalloys demonstrateddemonstrated, compatible , compatible withwith curingcuring

⇒⇒ Good aGood aptitudeptitude of the CMS insert to be cold reduced by roll shapingof the CMS insert to be cold reduced by roll shaping⇒⇒ Good aGood aptitudeptitude of the CMS insert to be cold reduced by roll shapingof the CMS insert to be cold reduced by roll shaping

⇒⇒ Intrinsic and heterogeneous Intrinsic and heterogeneous weldabilityweldability of the alloys demonstratedof the alloys demonstrated

Alternative solutions:Alternative solutions:

⇒ Not fully industrially confirmedNot fully industrially confirmed⇒⇒ Dispersion Dispersion strengthenedstrengthened or composite Alor composite Al--basedbased alloysalloys alternative alternative

to Alto Al--0.1wt%Ni 0.1wt%Ni shouldshould bebe the the objectobject of a of a carefulcareful design design

Toward an improved conductor,Toward an improved conductor,reinforcementreinforcement

S. Sequeira Tavares, S. Sgobba, J. of Mat. Proc. Technology143–144 (2003) 584–590