C51900 Bronze

Alloy Designation

• International: UNS C51900, CDA 519, CuSn6 (EN Standard)

• Chinese: QSn6.5-0.1 (GB/T 4423-1992)

• Alias: Tin-phosphor bronze, Instrument bronze, featuring 6-7% tin and 0.1-0.25% phosphorus.

Key Features

C51900 balances high strength with functionality:

• High Strength & Elasticity: Tensile strength ≥480 MPa (cold-worked), elastic modulus 115 GPa; ideal for precision springs.

• Corrosion/Wear Resistance: Corrosion rate <0.01 mm/year in atmosphere/freshwater; low friction coefficient (0.18-0.25).

• Special Properties: Non-magnetic (μ<1.01), spark-resistant for explosion-proof applications.

• Processing Flexibility: Excellent hot/cold workability, weldability, brazing, and machinability.

Product Forms & Dimensions

Table 1: Product Forms & Specifications

Form	Size Range	Temper	Standard
Sheet/Plate	Thickness: 0.1-50mm; Width: 100-1500mm	O60 (Soft), H08 (Hard)	ASTM B103
Strip	Thickness: 0.05-2.0mm; Width: 10-600mm	H04, H06	GB/T 4423
Bar (Round/Hex)	Diameter/Width: Ø5-200mm	Y2 (Half-hard), T6 (Aged)	ASTM B139
Wire	Diameter: Ø0.1-12mm	Soft, Half-hard	ASTM B103
Tube	OD: Ø3-150mm; Wall: 0.2-10mm	Annealed, Hard	GB/T 4423

Note: Custom sizes (e.g., hex bars, profiles) available with ±0.05mm tolerance.

Chemical Composition

Table 2: Chemical Composition (wt%, Cu bal.)

Element	Req.	Typical	Impurity Max	Function
Sn	6.0-7.0	6.5	–	Strength, hardness & corrosion resistance
P	0.10-0.25	0.15	–	Deoxidation, fluidity & wear resistance
Fe	≤0.05	≤0.02	0.05	Excessive amounts reduce conductivity
Pb	≤0.02	≤0.005	0.02	Controls hot shortness
Zn	≤0.30	≤0.10	0.30	Trace residual
Total Impurities	≤0.10	≤0.05	0.10	–

*Standards: GB/T 4423-1992, ASTM B139.*

Physical Properties

Table 3: Physical Properties (20°C)

Property	Value Range	Unit	Test Condition
Density	8.80-8.86	g/cm³	ASTM B193
Electrical Conductivity	15-16	%IACS	Annealed
Thermal Conductivity	38-42	W/(m·K)	Steady-state heat flow
CTE	18.5×10⁻⁶	K⁻¹	20-300°C
Elastic Modulus	110-115	GPa	Tensile test
Melting Point	1000-1020	°C	–

Mechanical Properties

Table 4: Mechanical Properties (Room Temp, Bar Samples)

Property	Annealed (O60)	1/4 Hard (H02)	Hard (H08)	Test Standard
Tensile Strength (σb)	≥325 MPa	≥480 MPa	≥620 MPa	ASTM E8
Yield Strength (σ₀.₂)	≥150 MPa	≥400 MPa	≥550 MPa	ASTM E8
Elongation (δ₅)	≥30%	≥13%	≥5%	GB/T 228.1
Hardness (HV)	85-100	150-180	200-230	ASTM E92
Fatigue Strength (10⁷ cycles)	140 MPa	240 MPa	300 MPa	Rotating bending

*Note: Sample diameter 5-12mm (longitudinal direction).

Core Advantages

• Strength-Conductivity Balance: 15-16% IACS + 480 MPa tensile strength (H02), outperforms C51000/C51100.

• Extended Wear Life: 2× longer bearing life vs. brass (PV limit: 2.5 MPa·m/s).

• Cryogenic Suitability: No brittleness at -200°C for aerospace/superconducting equipment.

• Processing Compatibility: Supports cold heading, stamping (≤30% deformation), TIG welding (SCu5210 filler).

Applications

• Electronics: High-reliability connectors, relay springs, test probes (>100k mating cycles).

• Precision Instruments: Hairsprings, diaphragms, brush holders, gears (non-magnetic).

• Industrial: Bellows, bearing bushes, chemical pump seals (resists weak acids/seawater).

• Transportation: Aircraft sensor springs, automotive seat brackets (cold-stamped).

Processing Guidelines

• Hot Working: Strictly 750-770°C; >800°C causes grain growth, <700°C increases deformation resistance.

• Cold Working: ≤30% per-pass reduction; intermediate anneal (600-650°C×1h) to relieve hardening.

• Welding: Prefer TIG (SCu5210 filler + 200-250°C preheat); post-weld anneal at 500-550°C.

• Surface Treatment: Avoid lead-containing coolants to prevent SCC; chromate passivation enhances corrosion resistance.

Key Application Scenarios

• Aerospace Connectors: Stable performance under high vibration (Airbus A350 certified).

• Marine Valve Bushings: ≥10-year design life in seawater.

• Smart Meter Springs: Elastic hysteresis <0.05% (meets Class 0.1 accuracy).

• Explosion-Proof Tools: Spark-free impact for oil platform maintenance.

FAQ

Q1: C51900 vs. QSn4-3 (C51100)?

A1: C51900 has higher Sn (6.5% vs. 4%), 30% higher strength/elasticity, but 20% higher cost. Use C51100 for general springs; C51900 for high-stress springs/wear parts.

Q2: Extra protection in seawater?

A2: Corrosion rate <0.015 mm/year (static). For flow >2 m/s, use passivation/cathodic protection; avoid direct contact with stainless steel.

Q3: Microcracks after cold working?

A3: Caused by excessive deformation/surface defects. Solutions:

1. Limit per-pass reduction to ≤25%;

2. Acid-clean oxide layers pre-processing;

3. Intermediate anneal (620°C×1h).

Q4: Insufficient hardness post-heat treatment?

A4: Verify parameters:

• Annealed: 600-650°C + air cooling;

• Aging: 320-340°C×2-3h (hardness ↑10-15%).

Reference Standards

Standard	Code	Title
China	GB/T 4423-1992	Wrought Copper Alloy Bars
	GB/T 5231-2012	Chemical Composition & Forms of Wrought Copper Alloys
USA	ASTM B103/B103M-2019	Phosphor Bronze Plate, Sheet, Strip, and Rolled Bar
	ASTM B139/B139M-2013	Phosphor Bronze Rod and Bar
International	ISO 427:2016	Wrought Copper Alloys – Composition & Product Forms
	EN 12163:2016	Copper and Copper Alloys – Rod for General Purposes (CuSn6 equivalent)
Japan	JIS C5191	Phosphor Bronze Strip for Electronic Equipment

Testing Standards

• Chemistry: ASTM E54 (Sn), ASTM E62 (P)

• Mechanical: ASTM E8 (tensile), ASTM E92 (hardness)

• Metallography: ASTM E112 (grain size)

Note: Data synthesized from ASTM, GB, JIS, and manufacturer specs. Performance may vary slightly with processing. Conduct application-specific validation before use.