Copper Chromium Zirconium (CuCrZr / C18150) Investment Casting: High Conductivity with High Strength

Copper Chromium Zirconium — CuCrZr, UNS C18150 — occupies a specific and important position in the copper alloy investment casting landscape. Investment casting of CuCrZr produces components that deliver electrical conductivity of 80–85% IACS alongside yield strength of 400–500 MPa in the age-hardened condition. This combination is not achievable in ETP copper (100% IACS conductivity but ~70 MPa yield strength in the annealed condition) or in aluminium bronze (comparable strength but 15–20% IACS conductivity).

CuCrZr fills the gap — and for the applications where both properties are simultaneously required, it is the only correct specification.

This guide covers the CuCrZr alloy, its composition and specification designations, the applications where its dual-property profile is mandated rather than merely preferred, the mandatory heat treatment sequence, and how it compares to the alternatives — including beryllium copper, whose occupational health profile is driving a broad industry transition toward CuCrZr.

The complete copper alloy investment casting family across all nine alloy sub-groups is covered in the Complete Guide to Copper, Brass, and Bronze Investment Casting, while the broader investment casting process across all material families is explained in Investment Casting: Process, Materials, and Industrial Applications — A Complete Guide.

The Dual-Property Problem — Why Most Copper Alloys Cannot Solve It

Electrical conductivity and mechanical strength are inversely related in most engineering metals. Alloying additions that strengthen a copper matrix by introducing secondary phases, solid-solution hardening, or precipitation hardening mechanisms also scatter conduction electrons — reducing conductivity. The engineering challenge for applications that carry both electrical current and structural load is finding an alloy that achieves an adequate level of both properties simultaneously.

In copper alloys, this trade-off plays out as follows:

Alloy	UNS	Conductivity	Yield Strength (aged/hardened)	Limitation
ETP Copper	C11000	100% IACS	~70 MPa (annealed)	Soft — insufficient strength for structural-electrical applications
OFHC Copper	C10200	≥101% IACS	~70 MPa (annealed)	Same strength limitation as ETP
Aluminium Bronze	C95500	15–20% IACS	350–450 MPa	Good strength — poor conductor
Brass CuZn37	C26800	28–30% IACS	~200 MPa	Neither adequate conductor nor adequate strength
CuCrZr	C18150	80–85% IACS	400–500 MPa	The exception — high in both. The correct specification for dual-property applications
Beryllium Copper	C17200	22–30% IACS	1,000–1,200 MPa	Highest strength in the copper family — but IARC Group 1 carcinogen. Being phased out.

CuCrZr achieves its dual-property profile through a precipitation hardening mechanism: chromium and zirconium additions, in very small quantities, precipitate as fine intermetallic particles on aging heat treatment. These precipitates block dislocation movement (providing strength) without significantly disrupting the copper matrix conductivity (preserving conductivity).

The result is a fully hardened CuCrZr casting at 80–85% IACS and 400–500 MPa yield — a combination that no alternative copper alloy matches without either a severe conductivity penalty or a severe strength penalty.

CuCrZr Composition and Specification Designations

CuCrZr is produced in a narrow composition range — small additions of chromium and zirconium in a high-purity copper matrix. The balance is critical: too little chromium and zirconium provides insufficient precipitation strengthening; too much increases resistivity and reduces conductivity below specification.

Element	Composition Range	Role
Copper (Cu)	Balance (~97–98.5%)	Primary matrix — conductivity carrier
Chromium (Cr)	0.5–1.5%	Primary precipitation hardening agent — Cr₂Zr and Cr precipitates provide the strength increment
Zirconium (Zr)	0.03–0.30%	Grain refinement and secondary precipitation — improves hot workability and softening resistance at elevated temperature
Other elements	< 0.15% total	Specified limits maintained to preserve conductivity

Standard	Designation	Reference
UNS (North America)	C18150	Copper Development Association — the standard procurement designation for CuCrZr
EN (Europe)	CW106C (Cu-Cr-Zr)	EN 12163 / EN 12166 — for wrought forms; EN 1982 for cast copper alloys
ASTM	B441 (rod), B758 (plate)	Wrought form references — cast equivalent specified by composition to UNS C18150
IS (India)	IS 1396 Part 1	Copper alloys — precipitation hardening grades

When specifying CuCrZr investment castings on a drawing, state UNS C18150 and the required heat treatment condition (solution treated and aged) alongside the mechanical property and conductivity requirements.

Specifying 'CuCrZr' or 'copper chromium zirconium' without the UNS designation and heat treatment condition leaves ambiguity that a foundry may not resolve to the buyer's advantage.

Heat Treatment — Mandatory for CuCrZr Investment Castings

CuCrZr investment castings supplied without heat treatment have not received the mechanical or conductivity properties of the specified alloy. As-cast CuCrZr is a soft, solid-solution copper alloy — the chromium and zirconium remain in solution in the copper matrix and do not provide their strengthening effect until precipitation is induced by the aging heat treatment sequence.

Condition	Yield Strength	Hardness	Conductivity	Notes
As-cast (no heat treatment)	~150–200 MPa	~60–80 HRB	~40–60% IACS	Chromium and Zr in solid solution — soft and low conductivity. NOT the specified condition.
Solution treated only	~150–180 MPa	~55–75 HRB	~50–65% IACS	Chromium and Zr in solution — soft. Intermediate step only, not the final condition.
Solution treated + aged (peak)	400–500 MPa	28–34 HRC	80–85% IACS	Precipitates formed — full strength and conductivity achieved. The specified condition.

The solution treatment and aging sequence is two distinct operations performed in the correct order: solution treatment dissolves the chromium and zirconium fully into the copper matrix, and water quenching locks them in solution.

Aging at a lower temperature then allows controlled precipitation of the strengthening phases. Reversing this order, omitting either step, or performing the aging at incorrect temperature or duration produces a casting that does not meet specification.

For procurement teams: always specify 'solution treated and aged per UNS C18150' on the purchase order and request the heat treatment certificate alongside the material certificate. A casting that skips heat treatment will appear dimensionally correct on delivery and fail in service — the dimensional check on arrival does not verify the mechanical or electrical properties.

Applications for Investment Casting CuCrZr

The applications that justify CuCrZr specification share a common characteristic: both conductivity and mechanical strength are simultaneously active design constraints. Where only conductivity matters, ETP copper is the correct and more economical specification. Where only strength matters, aluminium bronze or stainless steel is typically the correct specification. CuCrZr is mandated when both properties are required at the same time in the same component.

High-Pressure Electrical Contact Tips

Circuit breaker contact tips and high-pressure clamp contacts that carry current under mechanical clamping force require both a low-resistance conductor path (conductivity) and the ability to resist permanent deformation under the specified contact pressure (yield strength). ETP copper contact tips deform under clamping force, increasing contact resistance over service life. CuCrZr investment cast contact tips maintain dimensional integrity under contact pressure while providing the conductivity required for minimal resistive heating at the contact interface.

Current-Carrying Structural Members

Bus bar systems with structural integrity requirements — suspension hardware, clamping brackets, and connector bodies that are simultaneously part of the electrical conductor path and the mechanical support structure — require CuCrZr when the structural load is beyond the yield strength of standard copper grades. Investment casting produces these multi-function geometries as single components, eliminating the joints between the electrical conductor section and the structural support section that would be required in a fabricated design.

Stator Bar Connectors — High-Strength Requirement

Large generator stator bar connectors that require both high conductivity (to minimise I²R losses in the connector) and resistance to mechanical fatigue from generator vibration cycles are specified in CuCrZr rather than ETP copper.

The investment casting process produces the complex end-winding connector geometry as a near-net-shape component. For hydrogen-cooled generators specifically, CuCrZr shares the OFHC copper requirement for hydrogen embrittlement resistance — unlike ETP copper, CuCrZr's low oxygen content prevents the embrittlement that occurs in high-oxygen copper grades in hydrogen environments above 400°C.

For applications requiring strength beyond CuCrZr's capability — where 1,000 MPa yield strength is genuinely needed — the stainless steel investment casting range offers high-strength options including 17-4 PH (yield strength 1,000–1,170 MPa in the H900 condition) without the carcinogenic risk of beryllium copper.

The complete copper alloy grade selection context — from ETP and OFHC to high-performance alloys such as CuCrZr — is explored in detail across our guides: Complete Guide to Copper, Brass, and Bronze Investment Casting, OFHC vs ETP Copper: Which Grade Should You Investment Cast?, and Vacuum Investment Casting of Oxygen-Free Copper (OFHC).

Specifying CuCrZr Investment Castings — What to Include

Specification Item	What to State	Why It Matters
Material designation	UNS C18150 (or EN CW106C for EU procurement)	'CuCrZr' alone is insufficiently specific — the UNS code confirms the exact composition range
Heat treatment condition	'Solution treated and aged' — specify target hardness or yield strength range	Without specifying condition, foundry may supply as-cast (unaged) — meeting no strength requirement
Mechanical properties	Yield strength minimum (e.g. 400 MPa) and/or hardness range (e.g. 28–34 HRC)	Verifiable against the delivered casting on every batch
Conductivity requirement	'Minimum 80% IACS' — verified on sample from each heat	Confirms that aging was performed correctly and chromium/Zr have precipitated
Material certificate	EN 10204 Type 3.1 — specific measured values, not conformance declaration	Chemical analysis + mechanical test results from the actual production heat
Heat treatment certificate	Certificate confirming solution treatment temperature, time, quench, aging temperature and duration	Validates the heat treatment sequence was performed to specification

Source CuCrZr Investment Castings from Pahwa MetalTech

Pahwa MetalTech produces investment castings — also known as lost wax castings — in Copper Chromium Zirconium (CuCrZr / UNS C18150), solution treated and aged to full hardness specification. Conductivity verified to minimum 80% IACS on samples from each heat.

To discuss a CuCrZr investment casting requirement — contact us or write to us at info@pahwametaltech.co.in