Cu46 is a shorthand code that appears in spreadsheets, engineering drawings, and procurement lists.
Despite its cryptic appearance, the term unlocks precise material specs that can save both time and money.
Origin and Definition of Cu46
Cu stands for copper, the base element. The number 46 points to a specific alloy designation within the unified numbering system (UNS). UNS C46400—nickel-tin brass—is the full name hiding behind Cu46.
The alloy contains 59–62 % copper, 0.5–1.0 % tin, and the balance zinc plus trace elements like iron and lead. Tin adds seawater corrosion resistance. Zinc keeps the cost reasonable while maintaining machinability.
Unlike generic “brass,” Cu46 guarantees repeatable chemistry and mechanical properties. Engineers rely on that repeatability when designing valves, pump bodies, or marine hardware.
Material Properties at a Glance
Mechanical Strength
Yield strength hovers around 170 MPa in the annealed state. Cold working can push yield beyond 310 MPa without heat treatment. This range gives designers leeway to tune strength via forming processes.
Corrosion Resistance
Salt-spray tests show pitting depths of <0.05 mm after 1000 h. That performance rivals naval bronze at a fraction of the price. The tin-rich surface film self-repairs when scratched.
Thermal and Electrical Conductivity
Thermal conductivity sits at 115 W·m⁻¹·K⁻¹, double that of stainless steels yet half that of pure copper. Electrical conductivity is 26 % IACS, making Cu46 unsuitable for bus bars but perfect for heat sinks needing moderate conductivity plus corrosion resistance.
Key Industrial Applications
Marine Hardware
Propeller nuts, shaft sleeves, and strut bearings rely on Cu46 because the alloy resists dezincification in seawater. Its machinability allows tight threads without galling.
Valve and Pump Components
Gate valves in desalination plants use Cu46 stems and seats. The alloy tolerates chloride levels above 35,000 ppm while maintaining dimensional stability at 90 °C.
Forged Fittings
Hydraulic couplers rated to 200 bar often specify Cu46 forgings. Cold-forged grain flow improves fatigue life, and the tin content reduces internal erosion.
Heat Exchanger Tubes
Small-bore chillers in breweries use Cu46 tubing to handle both steam and glycol. The alloy limits copper pickup into the beverage stream.
Cu46 vs. Common Copper Alloys
C26000 cartridge brass is softer and more ductile but corrodes rapidly in saltwater. Cu46 sacrifices some formability for superior seawater durability.
C70600 90/10 cupronickel offers higher corrosion resistance yet costs 40 % more. Choose Cu46 when budgets are tight and biofouling is controlled by coatings.
Against silicon bronze C65500, Cu46 shows 15 % lower tensile strength but machines three times faster. Machining cost savings often outweigh raw material differences.
Supply Forms and Standards
ASTM B21 covers Cu46 rod, bar, and shapes. ASTM B171 governs plate and sheet. MIL-B-16444 sets naval specifications for forgings and castings.
Common stock sizes range from 6 mm rod to 150 mm diameter forging stock. Suppliers deliver hollow bar for seamless bushing production. Lead-time for custom extrusions is typically six weeks.
All reputable mills provide EN 10204 3.1 certificates. Ask for mercury content certification if the application involves potable water.
Design Guidelines
Stress Allowables
Design stress at room temperature should not exceed 55 MPa for static loads. Fatigue limit at 10⁷ cycles is 115 MPa in seawater.
Jointing Methods
TIG welding requires ERCuSi-A filler to prevent hot cracking. Silver brazing with BAg-5 works for non-critical joints. Mechanical joints using rolled threads avoid heat-affected zone softening.
Surface Treatments
Passivation in 2 % sodium dichromate solution improves corrosion resistance by 15 %. Electroless nickel plating adds lubricity for sliding valve stems. Avoid chromate conversion coatings in food-grade equipment.
Machining and Fabrication Tips
Use 140 m/min cutting speed with carbide tools for optimal chip control. Flood coolant keeps the tin-rich chips from welding to the tool edge. Peck drilling above 12 mm diameter prevents chip clogging.
Deep drawing is limited to 35 % reduction per pass. Intermediate annealing at 550 °C restores ductility. Springback compensation of 0.5 % is required for 90 ° bends.
When soldering, apply activated rosin flux within five seconds of iron contact. Prolonged heat drives off tin and weakens the joint.
Quality Control and Testing
Dimensional Checks
Use air gauging for internal bores tighter than IT8 tolerance. Laser scanning captures complex casting geometries in minutes.
Non-Destructive Evaluation
ASTM E426 eddy-current testing detects surface cracks as shallow as 0.1 mm. Immersion ultrasonic testing verifies wall thickness in tubing down to 1 mm.
Corrosion Validation
ASTM G48 Method A pitting tests expose coupons to 6 % ferric chloride for 72 h. Weight loss must stay below 2 mg/cm² to qualify a heat.
Cost Modeling and Sourcing
London Metal Exchange (LME) copper prices drive base cost, but tin premiums add volatility. Forward contracts on tin for six months can lock margins.
Scrap buyback programs return 65 % of raw material value. Segregate Cu46 chips from free-cutting brass to maintain scrap purity.
Regional mills in South Korea and India offer 8 % price advantages over European suppliers. Factor in shipping and 5 % duty when comparing landed costs.
Environmental and Regulatory Notes
RoHS compliance hinges on lead content below 0.1 %. Most Cu46 heats meet the limit without modification.
ISO 14064 audits track carbon footprint at 4.2 kg CO₂ per kg of Cu46 bar. Specify recycled content certificates for LEED credits.
End-of-life recovery rates exceed 85 % in regions with established scrap networks. Mark components with “Cu46” to aid recycling centers.
Future Trends and Alternatives
Additive Manufacturing
Research labs have printed Cu46 via laser powder bed fusion. Density reaches 99.6 % after hot isostatic pressing. Printed valve bodies cut lead time from weeks to days.
Higher-Tin Variants
Experimental Cu50 with 2 % tin promises 30 % better cavitation resistance. Cost projections show only 7 % premium if tin prices stabilize.
Digital Traceability
Blockchain-based mill certificates will soon travel with each bar. Scanning a QR code will reveal heat chemistry, forging date, and NDT results.
Quick Reference Cheat Sheet
UNS: C46400. Density: 8.41 g/cm³. Melting range: 885–900 °C. Machinability rating: 70 (free-cutting brass = 100). Weldability: Fair with Si-bronze filler.
Stock forms: Rod, bar, plate, tube, forging stock. Standards: ASTM B21, B171, MIL-B-16444. Typical yield: 170–310 MPa. Seawater corrosion: Excellent.
Design tip: Use 1.5× safety factor against pitting in stagnant seawater. Procurement tip: Book tin surcharge three months ahead to avoid price spikes.