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CuSn6 (Phosphor Bronze 6%)

CuSn6 β€” lower tin phosphor bronze. Excellent spring properties and corrosion resistance. For connectors, springs, sliding contacts and bushings.

Copper Alloys Tin Bronze ENCuSn6 / CW452K UNSC51900 ASTMB103 / B139 Alloy C51900 BS ENPB102 / CW452K +4
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Description

CuSn6 per EN 1652 (CW452K). 6% Sn gives good balance of spring properties, conductivity (13% IACS) and machinability. Slightly lower strength than CuSn8 but better electrical conductivity. Standard for medium-duty connector contacts, electrical springs, bushings and bearing inserts.

Key Properties β€” Annealed (O)
Rm (Tensile Strength)
350 – 480
MPa
Re / Rp0.2 (Yield)
140
MPa
Aβ‚… (Elongation)
β‰₯ 45.0
%
Hardness
80 – 120
HB
E (Young's Modulus)
115
GPa
Density
8.80
g/cmΒ³
Main Designations (8)
Standard BodyDesignationCountry / RegionNote
EN CuSn6 / CW452K EU
UNS C51900 USA
ASTM B103 / B139 Alloy C51900 USA
BS EN PB102 / CW452K UK
JIS C5191 Japan
GOST BrOF6.5-0.15 (BrOF6.5-0.15) Russia
Trade Phosphor Bronze Grade C / Spring Bronze Global
JUS C.Sn6P Yugoslavia Fosforna bronza 6% Sn; JUS B.C5.410
Standards (8)
#Standard BodyDesignationCountry / RegionNote
1 EN CuSn6 / CW452K EU β€”
2 UNS C51900 USA β€”
3 ASTM B103 / B139 Alloy C51900 USA β€”
4 BS EN PB102 / CW452K UK β€”
5 JIS C5191 Japan β€”
6 GOST BrOF6.5-0.15 (BrOF6.5-0.15) Russia β€”
7 Trade Phosphor Bronze Grade C / Spring Bronze Global β€”
8 JUS C.Sn6P Yugoslavia Fosforna bronza 6% Sn; JUS B.C5.410
All values in wt.%
Cu
Copper
~93.5000
Sn
Tin
5.5000 – 6.5000
P
Phosphorus
0.1000 – 0.2500
ElementSymbolMin %Max %Typical %
Copper Cu 93.0000 β€” 93.5000
Tin Sn 5.5000 6.5000 6.0000
Phosphorus P 0.1000 0.2500 0.1500
Mechanical Properties
ConditionCode Rm min
MPa		Rm max
MPa		 Re min
MPa		Re max
MPa		 Aβ‚… min
%		 Z
%		 KV
J		 HB minHB max HRC minHRC max E
GPa
Annealed (O) +O 350 480 140 β€” 45.0 β€” β€” 80 120 β€” β€” 115.0
Half Hard (H02) H02 480 640 380 β€” 20.0 β€” β€” 130 165 β€” β€” 115.0
Hard (H04) H04 590 750 510 β€” 10.0 β€” β€” 165 205 β€” β€” 115.0
Extra Hard (H06) H06 680 830 620 β€” 5.0 β€” β€” 195 230 β€” β€” 115.0
Physical Properties
Density
8.800
g/cmΒ³
Melting Point
975–1025
Β°C
Young's Modulus
115.0
GPa
Poisson's Ratio
0.340
β€”
Thermal Conductivity
71.0
W/mΒ·K
Thermal Expansion
18.00
Γ—10⁻⁢ /K
Specific Heat
380
J/kgΒ·K
Electrical Resistivity
0.1100
¡Ω·m
Magnetic
No
 
Heat Treatment
Annealing
Temperature:450Β°C – 700Β°C
Medium:Inert or reducing atmosphere
Duration:20-60 min
Cooling:Air or water cool
Hardness After:HB 80-120
Bright anneal for spring strip.
Stress Relief
Temperature:130Β°C – 200Β°C
Medium:Air oven
Duration:1-2 h
Cooling:Air cool
Hardness After:Minimal
After cold forming to improve spring set resistance.
Machinability
Machinability Rating
relative to AISI B1112 = 100%
45.0%
Difficult
Turning Speed (HSS)
175
m/min
Turning Speed (Carbide)
775
m/min
Feed Rate (Turning)
0.340
mm/rev
Drilling Speed (HSS)
150
m/min
Milling Speed (Carbide)
790
m/min
CoolantSoluble oil 5-8%
Chip FormationMedium chips (annealed); shorter in hard temper
Tool MaterialHSS M2; carbide K20
Surface FinishRa 0.4-1.6 um
Good machinability. Better than pure Cu due to Sn.
Applications
Electrical Springs
Precision connector springs, relay springs and contact springs β€” primary application.
Electrical Connectors
Socket contacts, crimp contacts and edge connector fingers.
Bearings
Plain bearing bushes in corrosive environments where steel would corrode.
Musical Instruments
Cymbals, bells and tambourines (80% of professional cymbals are CuSn8-12).
Technical Notes
βœ…
CuSn6 vs CuBe2 springs
CuSn6: 40% IACS conductivity, Rm 750 MPa H04, no hazard, low cost. CuBe2: 22% IACS, Rm 1400 MPa β€” 2x strength. Use CuBe2 when spring loads demand >750 MPa; CuSn6 for most electrical springs at lower load.
βœ…
P content
P (0.10-0.25%) deoxidises the melt (preventing tin oxide porosity) and slightly hardens β€” essential for spring properties. Specify phosphor bronze (not just tin bronze) for spring applications.