Joining and Welding Research Institute, OSAKA UNIVERSITY

Background ~ No more hazardous element, Pb

Temperature / ℃

α-β duplex brass alloys with “Pb” widely used in industries

α-phase(bcc)

α-phasePb

40mass%Cu

β-phaseβ-phase(fcc)

Zn (mass%)

50μm
Zn

Machinable Cu-40%Zn-3.2%Pb alloy

Joining and Welding Research Institute, OSAKA UNIVERSITY

Background ~ Effective elements for good machinability
Bismuth, Bi

Graphite particles

BiGr

50μm
Machinable Cu-40%Zn-2.7%Bi alloy

50μm

Machinable Cu-40%Zn alloy with 1.0%Gr• Toxic for human• Rare metal = expensive• Poor recyclability
Easy reaction of Bi with Pb
in re-melting of BS40
H. Imai, Y. Kosaka, A. Kojima, S. Li, K. Kondoh, J. Umeda,
H. Atsumi; Powder Technology, 198 (2010) 417-421.
Joining and Welding Research Institute, OSAKA UNIVERSITY

Objectives ~ Pb-free high-strength P/M Cu-40%Zn alloy
Materials design for high-strength Cu-40%Zn (BS40) by P/M route
Rapidly solidified alloy powder
Grain/phase boundaries (β)

Supersaturated
solid solution(Cr, Fe, Ti, Sn etc)

Wrought P/M Cu-40%Zn-X alloy
Solid solution hardening

β-phaseformation

Precipitates
Grain refinementin grain（1～5μm）（～500nm）
Precipitates at G.B （～1μm）→ Grain pinning effectJoining and Welding Research Institute, OSAKA UNIVERSITYP/M high-strength and machinable BS40-X alloys

Tensile strength, σ/ MPa

800

Stainless Powder metallurgy
BS40-Fe-Cr-Sn-Ti+Gr
steel(TS; > 700MPa)

700

Fe-Cr nano precipitatesat grain boundary(200~500nm)

P/M BS40-Fe-Cr-Sn+Gr(TS; > 600MPa)

600

Cu-30Zn-Al-Si

P/M BS40-Ti/Cr+Gr(TS; > 500MPa)

500

P/M BS40+Mg+Gr400

BS40-0.7Fe-0.3Cr-0.3Sn+0.5Gr(TS; > 550MPa)

Cu-40Zn-Bi

Cu-40Zn-Pb
300
0246

Machinability (drilling speed) *10-2 / s-1
K. Kondoh et al., Journal of Metallurgy (2009) Article ID 853092.
Shufeng Li et al., J. Alloys and Compounds 493 (2010) 128–133.
Shufeng Li et al., J Materials Science (2010) 45:5669–5675.
H. Imai et al., Materials Transactions 52 (2011) 1426-1430.
Shufeng Li et al., Powder Technology 205 (2011) 242–249.
Shufeng Li et al., Materials and Design 32 (2011) 192–197.

Fe-Cr nano precipitates
inside grains（Fe35Cr65）
100 nmJoining and Welding Research Institute, OSAKA UNIVERSITY

Strengthening of BS40 alloy with elemental Mg addition
Mg NOT effective to improve strength of BS40 with Pb/Bi

Temperature /℃

Mg-Pb• Mg-Pb & Mg-Bi coarse intermetallics synthesized
via Mg-Pb/Bi reaction cause poor machinability andmechanical properties of BS40 alloy with Pb/Bi
Mg2Pb

Mg

Mass% Lead

◇ Bi

◇ Mg3Bi2
Cu-40Zn-3.2Bi

Pb

Mg-Bi
Temperature /℃

Mg3Bi2
Mg3Bi2Mg

Mass% Bismuth

Cu-40Zn-3.2Bi-1.0Mg

Cu-40Zn-3.2Bi-1.0Mg202530
3540
Diffraction angle, 2θ /deg

BiJoining and Welding Research Institute, OSAKA UNIVERSITY

45

Strengthening of BS40 alloy with elemental Mg addition
Mg additives for fine precipitation & grain refinement of BS40+Gr
Mg-C• No formation of Mg-C IMCs;
graphite particles effective for goodmachinability remain in the matrix.

Molten Mg

Gr plate

Mg2C3, MgC2; unstable phase
B. Hu, Y. Du, H. Xu, W. Sun, W.W. Zhang, D. Zhao,
Thermodynamic description of the C-Ge and C-Mg
systems

Poor wettability of graphite
plate by molten Mg droplet
N. Shinozaki, Jun Morita, K. Wasai, Wetting ofgraphite by molten magnesium, Journal of Japan
Institute of Light metals, 55 (2005) 310-314

Joining and Welding Research Institute, OSAKA UNIVERSITY

Today’s topics
Effect of Mg powders addition on microstructures of BS40 alloys
Mechanical properties and machinability of BS40 +Mg +Gr alloy
Cu-40%Zn alloy(BS40) powders++Graphite particles
Mg powders

Solid-state sintering
Pre-heating for solid solution of Mg
Hot extrusion
 Precipitation for fine microstructures
Joining and Welding Research Institute, OSAKA UNIVERSITYExperimental - raw powders
Chemical compositions
PowderPbOFeAlZn

CuMg

Cu-40Zn

0.005

0.090.003

0.005

40.42

Bal.

---

Pure Mg------

0.006

0.006

0.003

0.001

Bal.

BS40 powder (146 μm)

Pure Mg
Mg
BS40

Pure Mg powder(182 μm)

Cu-40Zn

BS40+1.0%Mg

Cu-40Zn+1.0Mg
120

Heating ratio 10 K/min in Ar

ΔTGA

100

80

500μm

500μm

DTA /uV60
40

Additive Mg powders;+0.5, 1.0, 1.5 mass%
Additive Gr particles;+0.75 and 1.25 mass%(Mg; 1.0%)8020600-20Graphite particles (4.8 μm)

CuZnMg IMC
formation at 815 K-4040DTA-80273

20

IMC decompositionat 973 K.

-60
473

673

87301073

Temperature, T /K

50 μm
Joining and Welding Research Institute, OSAKA UNIVERSITYΔTGA (%)

100120Experimental – consolidation by SPS and hot extrusion• Elemental mixtures of BS40, Mg and graphite powders(a-1) BS40 (Cu-40%Zn)(a-2) BS40 +0.5mass%Mg(a-3) BS40 +1.0mass%Mg(a-4) BS40 +1.5mass%Mg

Pressure

Carbon punch
Carbon Container

Starting powders

Mixedpowder

Thermo couple
insert hole(b-1) BS40+1%Mg +0.75%Gr(b-2) BS40+1%Mg +1.25%Gr• SPS: 973K for 1.8 ks under 30 MPa (in vac.)• H/E: pre-heating at 973K for 0.9 ks in Ar gas
 Mg solid solution into α&β phases
and fine precipitates (CuZnMg)
during cooling after hot extrusion• Microstructural - mechanical performance andmachinability evaluation of wrought specimens:
SEM-EDS, EBSP, XRD, tensile and drilling test

Spark plasma sintering (SPS)
LoadContainerPunch
Brass billetDieExtrudedbrass alloy

Hot extrusion

Joining and Welding Research Institute, OSAKA UNIVERSITY

Microstructural analysis on SPSed specimens• CuZnMg (1:1:1) IMCs precipitation duringcooling from 815K to R.T. in SPS(a-1) BS40 (Cu-40%Zn)(a-2) BS40 +0.5%Mg
β-phaseβ-phaseα-phaseCuZnMgCuMgZnβ-phase(a) BS40 (Cu-40%Zn)

Intensity /a.u.

• β phase fraction increasing with increase inMg content: Mg effective for β stabilization

Resin

(111)

(110)

(b) BS40 +0.5%Mg(c) BS40 +1.0%Mg
(111)

(311)

(220)
(d) BS40 +1.5%Mg

CuZnMg50μm(a-3) BS40 +1.0%Mg
β-phaseα-phaseCuZnMgCuZnMgα-phase50μm(a-4) BS40 +1.5%Mg

β-phase

50μm

50μm

303540453530252015α-phase25

Diffraction angle, 2θ /deg.
β-phase fraction (%)α-phase

20

29.3

32.6

32.0

23.5

Cu - 4 0 Zn

BS40

Cu - 4 0 Z n+0.5Mg+ 0. 5M g

Cu - 4 0 Zn+1.0Mg+1 . 0 M g

Cu - 4 0 Zn+1.5Mg+1 . 5 M g

Joining and Welding Research Institute, OSAKA UNIVERSITYMicrostructural analysis on SPSed specimens(a) BS40 (Cu-40%Zn)(b) BS40 +0.5%Mg
α-phaseβ-phase70μm70μm(c) BS40 +1.0%Mg

Increase of Mg content(d) BS40 +1.5%Mg

CuZnMgIncrease in area
fraction of β phaseMg; β stabilization

CuZnMg70μm

70μm
Joining and Welding Research Institute, OSAKA UNIVERSITY

Microstructural analysis on hot extruded specimens• CuZnMg (1:1:1) IMCs precipitation during cooling from 815K to R.T.
• β phase fraction increasing with increase in Mg content• Refinement of grains & IMCs in α&β phases(a-2) BS40 +0.5%Mg

β-phaseβ-phaseCuMgZnα-phase10μm

α-phaseα-phase

10μm

CuZnMgCuMgZnβ-phase(a) BS40 (Cu-40%Zn)

Intensity /a.u.

(a-1) BS40 (Cu-40%Zn)

Resin(b) Cu-40Zn +0.5%Mg(c) Cu-40Zn +1.0%Mg(d) Cu-40Zn +1.5%Mg
2020252530
3035
340540Diffraction angle, 2θ /deg.

(a-3) BS40 +1.0%Mg
CuZnMg(a-4) BS40 +1.5%Mg

β-phaseβ-phaseCu-40Zn+0.5Mg
CuZnMgCuZnMg

α-phase10μm

α-phase

10μm

5 μm

Joining and Welding Research Institute, OSAKA UNIVERSITY

4545Microstructural analysis on hot extruded specimens(a) BS40 (Cu-40%Zn)(b) BS40 +0.5%Mg
α-phaseβ-phase

35um

35um

(c) BS40 +1.0%Mg(d) BS40 +1.5%Mg
CuZnMgCuZnMg35um

35um
Joining and Welding Research Institute, OSAKA UNIVERSITY

Microstructural analysis on hot extruded specimens(a) Hot extruded specimens
6.38

6Grain size /μm

Grain size /μm

α-phaseβ-phaseα+β75.12543.323.16

32(b) SPSed specimens

4083530252015α-phase
β-phaseα+β105000.5

1Content of Mg additive (mass%)

1.500.5

11.5

Content of Mg additive (mass%)

CuZnMgCuZnMg35um

Hot extruded Cu-40%+1.5%Mg

70μm

SPSed Cu-40%+1.5%Mg
Joining and Welding Research Institute, OSAKA UNIVERSITY

Microstructural analysis on hot extruded specimens
8Grain size /μm

7α-phase
β-phaseα+β6.38

6ⅢCu-40Zn+1.5Mg

Ⅰ5.12

54Ⅲ
3.32

Ⅱ
3.16

35 μm

200.511.5

Content of Mg additive (mass%)
ⅡCu-40Zn+1.0Mg

ⅠCu-40Zn+0.5Mg

5 μm

5 μm

Joining and Welding Research Institute, OSAKA UNIVERSITY

Grain refinement mechanism of Cu-40%Zn by Mg additive

SPSed

IMCs solid solution
in pre-heating
Solid solution and phasetransformation

α-phaseβ-phaseIMCs

Hot extrusion

Cooling

Precipitation in grain and atgrain boundaries anddynamic recrystallizationof β-phase

Phase transformation（β→ α+β）

α-phase(with solid solution of Mg)
β-phase(with solid solution of Mg)

β-phasePrecipitates

Extrudedα-phaseβ-phasePrecipitates

Cu-40Zn+0.5Mg

Cu-40Zn+1.0Mg

5 μm
Transversal cross-section of the extrusion direction

Cu-40Zn+1.5Mg

5 μm

5 μm

Joining and Welding Research Institute, OSAKA UNIVERSITY

Mechanical properties of hot extruded specimens
532

531

45
40500

464

450

35

31

30

25

25

400
350

328

300

20323
14300

200

15
10229

250

5BS40+0.5Mg+1.0Mg

+1.5Mg600

Nominal stress, σ /MPa50(c) Cu-40Zn+1.0Mg

550
5000360

Yield strength, σy /MPa

41550

553

Elongation (%)

Tensile strength /MPa

600(c) Cu-40Zn+1.0Mg

340(d) Cu-40Zn+1.5Mg

320300280(b) Cu-40Zn+0.5Mg

k = 506 MPa/μm-1/2

2602402200.35(a) Cu-40Zn

0.4

0.45

0.50.550.6dα-β-1/2 /μm -1/2

Hall-Petch coefficient of conventional α-βbrass alloy with no additive:

450* k = 541 MPa/μm-1/2

400350(b) Cu-40Zn+0.5Mg*E. Werner, H. P. Stijwe, Phase Boundaries as300250(a) Cu-40Zn(d) Cu-40Zn+1.5Mg

200
00.1

0.2

Obstacles to Dislocation Motion, Materials Scienceand Engineering, 68 (1984-1985) 175-182.

0.30.4

0.5

Nominal strain, εJoining and Welding Research Institute, OSAKA UNIVERSITY

Fractured surface analysis on tensile test specimens
Cu-40%Zn alloy

50μm

Cu-40%Zn +1.5%Mg alloy

50μm

CuMgZn10μm

10μm

Joining and Welding Research Institute, OSAKA UNIVERSITY

Quantitative microstructural analysis on BS40+Mg+Gr alloy
Additive Gr particles effect on machinability
Estimation of Graphite particles area fraction
in matrix of extruded Cu-40Zn+1.0Mg+Gr

Average of 6 images in analysis;
Gr content(%)

Area fraction of Gr
particles in matrix (%)

0.5
0.75
1.0
1.25

1.84
2.76
3.68
4.60

Analysis result
182 μm

BSI242 μm

Ex. Area fraction of Gr particles in matrix: 4.82 %Number of dispersed Gr particles: 3,394
in case of Cu-40%Zn+1%Mg+1.25%Gr alloy

Area fraction of Gr particles

Machinability dependence on microstructures,in particular graphite dispersoids in matrix
0.06
0.05
0.04
0.03
0.02

Cu-40Zn+Gr

0.01

Cu-40Zn+Mg+Gr

000.5

1Gr content (mass%)
Joining and Welding Research Institute, OSAKA UNIVERSITY

1.5

Machinability evaluation of BS40+Mg+Gr alloy
TiAlN coated HSS drill
Diameter, D: 4.5mm
Helix angle: 30°
Point angle, α : 120°(a) Cu-40%Zn+1.0%Mg
N=1

N=10

♣ Rotating speed, N: 1140 (rpm)♣ Cutting speed, V: 268.3 (mm/sec)♣ Axial thrust load: 150 (N)♣ Dry condition (no lubricant)Specimen

Measurement of drilling time for 5mm depth hole
 Feed speed, F (mm/s); machinability parameter(b) Cu-40%Zn+1.0%Mg+0.75%Gr
N=1

N=10Feed speed, F (mm/s)

0.9(c) +1Mg+1.25%Gr0.80.70.60.5(c) Cu-40%Zn+1.0%Mg+1.25%Gr
N=10N=1(b) +1Mg+0.75Gr

0.40.30.20.1(a) +1Mg

012345678

Number of drilling test, N

910Joining and Welding Research Institute, OSAKA UNIVERSITY

Machinability evaluation of BS40+Mg+Gr alloy• Machinability improvement in proportion
to volume fraction (density) of Gr additives(a) Cu-40Zn(F=0.257 mm/s)(b) BS40 +0.5Mg(F=0.263 mm/s)(c) BS40 +1.0Mg(F=0.291 mm/s)(d) BS40 +1.5Mg(F=0.322 mm/s)

1st feed speed, F 1(mm/s)• Brittle CuZnMg IMC dispersoids also
effective for good machinability due toorigin in micro-crack initiation
1.2
10.8
0.6
0.4

Cu-40Zn

0.2

Cu-40Zn+Gr
Cu-40Zn+Mg+GrBS40+0.5Mg

60000

CuZnMg IMC

0020000

40000

80000

BS40+1.5Mg

Gr particle density, mm-25 μm

5 μm

Joining and Welding Research Institute, OSAKA UNIVERSITY

Quantitative microstructural analysis on BS40+Mg+Gr alloy
Extruded Cu-40Zn+1.0Mg+1.25Gr

CuMgZnGraphite

Transverse cross-section of extrusion direction

BSI –Middle brightness

BSI –High brightness

CuMgZnGrGr

Joining and Welding Research Institute, OSAKA UNIVERSITY

Summarized In using elemental mixture of Cu-40%Zn alloy and pure Mg powders andconsolidating them by SPS and hot extrusion, β phase fraction increased withincrease in the content of Mg additives.
 At the same time, grain refinement of α and β phases occurred because
dynamic recrystallized grains never grew after extrusion by pinning effect ofCuZnMg fine precipitates dispersed at grain boundaries.
 The mechanical property, in particular yield stress, was drastically improvedby Mg addition of wrought BS40 alloys.
 Additive graphite particles were obviously effective to improve machinabilityof BS40+Mg+Gr alloys because stable Mg-C IMCs were never formed duringconsolidation by SPS and extrusion.
Acknowledgement
This study was financially supported by University-Industries collaboration
program promoted in Japan Science and Technology Agency (JST).

Joining and Welding Research Institute, OSAKA UNIVERSITY