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CuNi2Si (Corson Alloy -- High-Strength Conductive Copper)

CuNi2Si (Corson alloy) -- Ni2Si precipitation-hardened copper giving high strength with good conductivity, and critically, excellent stress relaxation resistance at moderately elevated temperature. For high-force electrical connector springs, automotive connector terminals and relay springs.

Copper Alloys Precipitation Hardening Copper EN 12163CuNi2Si / CW111C DIN W.NrCW111C UNSC70250 ASTMB740 Alloy C70250 +2
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Description

CuNi2Si (CW111C / C70250) per EN 12163. Ni2Si intermetallic precipitates give Rm 550-650 MPa with 35-40% IACS conductivity, combined with notably better stress relaxation resistance than plain CuSn phosphor bronzes at 100-150 C -- the temperature range many automotive and under-hood electrical connectors actually experience in service. Standard for high-force connector springs, automotive terminal contacts, and relay springs requiring long-term contact force retention under thermal cycling.

Key Properties — Solution Annealed (O)
Rm (Tensile Strength)
300 – 420
MPa
Re / Rp0.2 (Yield)
120
MPa
A₅ (Elongation)
≥ 30.0
%
Hardness
75 – 105
HB
E (Young's Modulus)
130
GPa
Density
8.80
g/cm³
Main Designations (6)
Standard BodyDesignationCountry / RegionNote
EN 12163 CuNi2Si / CW111C EU
DIN W.Nr CW111C Germany
UNS C70250 USA
ASTM B740 Alloy C70250 USA
Trade Corson Alloy / TM03 / EFTEC-64T (various suppliers) Global
JUS C.Ni2Si Corson legura; nema JUS Yugoslavia/BiH CuNi2Si za konektore visoke sile
Standards (6)
#Standard BodyDesignationCountry / RegionNote
1 EN 12163 CuNi2Si / CW111C EU —
2 DIN W.Nr CW111C Germany —
3 UNS C70250 USA —
4 ASTM B740 Alloy C70250 USA —
5 Trade Corson Alloy / TM03 / EFTEC-64T (various suppliers) Global —
6 JUS C.Ni2Si Corson legura; nema JUS Yugoslavia/BiH CuNi2Si za konektore visoke sile
All values in wt.%
Cu
Copper
~96.7000
Ni
Nickel
1.6000 – 2.2000
Si
Silicon
0.4000 – 0.7000
Mg
Magnesium
≤ 0.2000
ElementSymbolMin %Max %Typical %
Copper Cu — — 96.7000
Nickel Ni 1.6000 2.2000 1.9000
Silicon Si 0.4000 0.7000 0.5500
Magnesium Mg — 0.2000 0.1000
Mechanical Properties
ConditionCode Rm min
MPa		Rm max
MPa		 Re min
MPa		Re max
MPa		 A₅ min
%		 Z
%		 KV
J		 HB minHB max HRC minHRC max E
GPa
Solution Annealed (O) +O 300 420 120 — 30.0 — — 75 105 — — 130.0
Peak Aged (H06) H06 550 650 500 — 8.0 — — 155 185 — — 130.0
Physical Properties
Density
8.800
g/cm³
Melting Point
1090–1120
°C
Young's Modulus
130.0
GPa
Poisson's Ratio
0.340
—
Thermal Conductivity
105.0
W/m·K
Thermal Expansion
17.00
×10⁻⁶ /K
Specific Heat
385
J/kg·K
Electrical Resistivity
0.0470
µΩ·m
Magnetic
No
 
Heat Treatment
Solution Annealing
Temperature:900°C – 950°C
Medium:Water quench
Duration:15-30 min
Cooling:Rapid quench
Hardness After:Rm ~350 MPa -- soft, formable
Precipitation Aging
Temperature:450°C – 480°C
Medium:Air or inert atmosphere oven
Duration:2-4 h
Cooling:Air cool
Hardness After:Rm 550-650 MPa / 35-40% IACS
Ni2Si precipitation gives combined strength and stress-relaxation resistance.
Stress Relief (after stamping)
Temperature:180°C – 220°C
Medium:Air oven
Duration:30-60 min
Cooling:Air cool
Hardness After:Minimal
After connector spring stamping.
Stress relaxation resistance (key property)
Temperature:100°C – 150°C
Medium:Sustained load at elevated temperature
Duration:1000+ h typical test
Cooling:N/A
Hardness After:Retains >80% of initial contact force
Significantly better than phosphor bronze (CuSn) at this temperature range -- the specific reason for selection in under-hood automotive connectors.
Machinability
Machinability Rating
relative to AISI B1112 = 100%
42.0%
Difficult
Turning Speed (HSS)
155
m/min
Turning Speed (Carbide)
700
m/min
Feed Rate (Turning)
0.290
mm/rev
Drilling Speed (HSS)
130
m/min
Milling Speed (Carbide)
710
m/min
CoolantSoluble oil 5-8%
Chip FormationMedium ductile chips
Tool MaterialHSS M2; carbide K20
Surface FinishRa 0.4-1.6 um
Good machinability where required, though primarily used as stamped connector strip.
Applications
Automotive Connectors
High-force automotive terminal and connector springs exposed to under-hood temperatures.
Relay Springs
Relay contact springs requiring long-term force retention.
High-Force Electrical Springs
General electrical connector and switch springs where CuSn phosphor bronze relaxation is inadequate.
Technical Notes
✅
CuNi2Si vs CuSn6 (phosphor bronze) vs CuBe2 for connectors
CuSn6: good general connector spring, but stress-relaxes measurably above about 80-100 C over time -- can lose contact force in hot automotive environments. CuNi2Si: significantly better relaxation resistance to 150 C, similar conductivity, no Be handling hazard. CuBe2: best-in-class relaxation resistance and strength, but toxic Be dust hazard. CuNi2Si is increasingly the preferred Be-free option for automotive connectors specifically because it addresses the thermal relaxation failure mode that limits ordinary phosphor bronze in engine-bay applications.