CuCr and CuCrZr Investment Casting: Alloys, Applications, Heat Treatment and Procurement Guide

The Bottom Line

• The copper chromium alloy family - CuCr (UNS C18200) and CuCrZr (UNS C18150) - exists to solve one engineering problem: carrying high electrical current and real structural load in the same component.

  
  

• An age-hardened CuCrZr investment casting delivers 80-85 percent IACS conductivity at 400-500 MPa yield strength, a combination no other copper alloy offers - but only when the casting has actually received its full heat treatment, which is why specifying and verifying the aged condition matters as much as choosing the alloy.

  
  

• Most copper alloys force a choice: pure copper grades conduct superbly but are too soft for structural-electrical duty, while the strong bronzes conduct poorly. The copper chromium family is the engineered exception - high in both properties at once.

  
  

• Heat treatment is the alloy: an as-cast or under-aged CuCrZr casting meets neither its strength nor its conductivity specification - only the

  complete solution-treat-and-age sequence produces the precipitates that deliver the rated properties.

  
  

• The industry is moving away from beryllium copper: with beryllium classified as an IARC Group 1 carcinogen, buyers who once defaulted to BeCu are adopting CuCrZr wherever 400-500 MPa yield strength is sufficient.

This pillar guide covers both grades of the family, the dual-property gap they fill, the mandatory heat treatment sequence, the applications where the alloy family is required rather than merely preferred, and exactly what to put on a drawing to receive castings that meet specification. The wider copper alloy casting family is covered in the Complete Guide to Copper, Brass, and Bronze Investment Casting, and the investment casting process itself across all material families in Investment Casting: Process, Materials and Industrial Applications - A Complete Guide.

The Dual-Property Problem in Copper Alloys

Strength and conductivity fight each other in copper. Every mechanism that strengthens a copper matrix - dissolved alloying atoms, second phases, retained cold work - also scatters the conduction electrons that make copper valuable in the first place. A design that needs a component to be both a conductor and a load-bearing part therefore runs into a wall with most of the standard alloy choices: the conductive grades are soft, and the strong grades are resistive. The consequences of ignoring this - specifying soft pure copper for a part that carries clamping force at temperature - are covered in why pure copper fails for high temperature switchgear applications. The table below shows how the trade-off plays out across the common copper alloy choices:

Alloy	UNS	Conductivity (IACS)	Yield Strength	Where It Falls Short
ETP copper	C11000	~100%	~70 MPa (annealed)	Too soft for structural-electrical duty
OFHC copper	C10200	~101%	~70 MPa (annealed)	Same softness as ETP
Aluminium bronze	C95400/C95500	~8-13%	~350-450 MPa	Strong, but a poor conductor
Brass (CuZn37)	C26800	~27%	~200 MPa (cold worked)	Adequate at neither property
CuCrZr	C18150	80-85% (aged)	400-500 MPa (aged)	The exception - high in both
Beryllium copper	C17200	~22-28% (aged)	1,000-1,200 MPa (aged)	Strongest copper alloy, but an IARC Group 1 carcinogen being phased out

The copper chromium family escapes the trade-off through precipitation hardening. Chromium - and in CuCrZr, a small zirconium addition - is dissolved into the copper matrix during solution treatment and then precipitated back out as fine particles during aging. The particles obstruct dislocation movement, which is what raises strength; and because the strengthening elements have left the copper lattice, they no longer scatter electrons, which is what recovers conductivity. Strength and conductivity rise together during aging instead of trading against each other - the metallurgical trick that makes the whole alloy family work.

Two Grades, One Family: CuCr and CuCrZr

The family has two commercial grades. CuCr (C18200) is copper with 0.6-1.2 percent chromium. CuCrZr (C18150) adds a small zirconium addition - typically 0.05-0.25 percent - on a similar chromium base. At room temperature the two behave almost identically; the zirconium earns its place at elevated temperature, where it restrains precipitate coarsening and meaningfully raises softening resistance - CuCrZr's softening onset runs roughly 470-500 degrees C - and refines the cast grain structure. CuCrZr vs CuCr: which copper chromium alloy should you specify and why covers the selection decision in full, and C18150 vs C18200 goes deeper into the temper and condition differences between the two grades.

Element	CuCr (C18200)	CuCrZr (C18150)	Role
Copper	Balance	Balance (~97-98.5%)	The matrix - carries the conductivity
Chromium	0.6-1.2%	0.5-1.5%	Primary precipitation hardening agent
Zirconium	-	0.05-0.25%	Restrains precipitate coarsening, refines grain, raises softening resistance
Others	Tightly limited	Tightly limited	Impurity limits preserve conductivity

On a drawing, name the grade by its designation rather than by the family name. 'CuCrZr' alone leaves the composition, and therefore the delivered properties, open to interpretation. The designations to use:

System	CuCr	CuCrZr
UNS (North America)	C18200	C18150
EN (Europe)	CW105C	CW106C - cast copper alloys under EN 1982
RWMA (electrode class)	Class 2	Class 2 (per AWS J1.3/J1.3M)

Heat Treatment: What Makes or Breaks the Casting

A CuCrZr casting that has not been correctly heat treated is not CuCrZr in any property sense - it is a soft, resistive solid-solution alloy wearing the right chemistry. The chromium and zirconium only strengthen the casting, and only stop scattering electrons, once the aging treatment has precipitated them out of the matrix. That happens in two distinct operations in a fixed order: solution treatment dissolves the alloying elements fully into the copper and a quench locks them there; aging at a controlled lower temperature then precipitates them back out as the strengthening particles. Skip either step, reverse the order, or cut the aging short, and the casting will fail its specification - while still passing every dimensional check on receipt.

Condition	Yield Strength	Hardness	Conductivity	Meets Specification?
As-cast / under-aged	Low - well below rating	Low, variable	Low - chromium still in or partly in solution	No - neither property at rating
Solution treated only	~150-180 MPa	Soft	~40-50% IACS	No - intermediate step only
Solution treated + aged	400-500 MPa	~120-180 HV (roughly 70-100 HRB)	80-85% IACS	Yes - the specified condition

For a buyer, the operational lesson is that incoming inspection has to test properties, not just dimensions: a hardness check as the fast screen and an eddy-current conductivity test in percent IACS as the real acceptance criterion. The full verification methodology - exactly what to put on the drawing and how to confirm correct aging on receipt - is covered in heat treatment and conductivity in CuCr castings.

Applications for CuCrZr Investment Casting

The applications that genuinely require this alloy family share one signature: conductivity and strength are both active design constraints in the same part at the same time. Where only conductivity matters, pure copper is the correct and cheaper answer; where only strength matters, a bronze or stainless grade usually is. CuCrZr belongs where neither compromise works.

Switchgear Contacts and Interrupter Hardware

Contacts that carry current under sustained mechanical clamping force are the alloy family's home ground. A soft copper contact deforms under contact pressure and its resistance climbs over service life; a CuCrZr contact holds its geometry and its clamping force while still conducting well enough to keep interface heating low. Tulip contact architecture in vacuum circuit breakers and VCB support electrodes are the clearest examples - components where holding spring force over the interrupter's service life is the entire design intent.

Current-Carrying Structural Hardware

Some components are simultaneously part of the current path and part of the supporting structure - busbar suspension hardware, clamping brackets, and connector bodies that carry both amperes and mechanical load. Investment casting produces these multi-function shapes as single monolithic parts, removing the bolted joints a fabricated design would need between its conductor and structural sections. GIS disconnector links and jaws sit squarely in this category: parts where one under-strength or relaxed component raises resistance across an entire current path.

The same current-carrying-plus-structural requirement is emerging in battery energy storage systems and broader industrial power distribution, where high-current busbar connectors and enclosure hardware sit in confined, thermally sensitive cabinets. As BESS and industrial current-carrying infrastructure deployments scale up, this is a growing application area for the alloy family - covered in more depth, alongside the related EV-charging-infrastructure angle, in substation hardware behind megawatt EV charging infrastructure.

Generator and High-Duty Connectors

Large generator stator bar connectors need low resistive losses and fatigue resistance against continuous vibration - the dual-property requirement again, plus complex end-winding geometry that suits near-net-shape casting. In hydrogen-cooled generators the alloy brings one more advantage: like OFHC copper, CuCrZr's low oxygen content resists the hydrogen embrittlement that attacks high-oxygen copper grades in hot hydrogen environments.

Conformally-Cooled Tooling: An Emerging Opportunity

A newer application lies outside the alloy family’s traditional electrical territory: conformally-cooled mold and die inserts, including for aerospace composite and polymer tooling, where cooling channels follow the part’s internal geometry rather than running in straight drilled lines. These inserts are usually produced by metal additive manufacturing today, since 3D printing is the only practical route to the curved internal channels - but CuCrZr’s high thermal conductivity is exactly the property that makes conformal cooling worthwhile, and investment casting can reproduce many of the same near-net internal channel geometries at a fraction of additive manufacturing’s per-part cost. This is a growing opportunity rather than an established track record for Pahwa MetalTech today, but as tooling buyers look for a lower-cost route to conformal cooling than metal 3D printing, investment-cast CuCrZr inserts are worth watching.

Two boundary notes complete the application picture. Where a design genuinely needs yield strength around 1,000 MPa - beyond what any aged CuCrZr casting delivers - a precipitation-hardening stainless grade such as 17-4 PH is the honest answer, without beryllium copper's health baggage. And the manufacturing route matters as much as the alloy: hot forging can compromise the very precipitation-hardening response that makes this family work, which is why the CuCrZr investment casting vs hot forging comparison matters before the purchase order is placed.

For buyers weighing this family against the pure copper grades, the wider selection context lives in OFHC copper vs ETP copper: understanding the grade difference and OFHC copper investment casting vs hot forging.

The Beryllium Copper Transition

For decades, beryllium copper (C17200) was the default answer when a copper alloy needed serious strength - and at 1,000-1,200 MPa aged yield it remains the strongest of the family. But beryllium is classified as a Group 1 carcinogen by the IARC, and the machining, grinding, and handling controls its dust demands have turned BeCu into a liability that procurement teams increasingly decline to carry. The practical replacement path is straightforward: for the large majority of switchgear, contact, and connector applications, the strength actually required sits within CuCrZr's 400-500 MPa envelope - with better conductivity than BeCu and none of the occupational health burden. Only the narrow band of applications that truly need four-digit yield strength must look beyond the copper family altogether.

Casting Capability at Pahwa MetalTech

Pahwa MetalTech casts the copper chromium family across a weight range of 0.005 kg to 70 kg, with the solution treatment and aging performed in-house rather than passed to a generic outside vendor - the heat treatment that defines this alloy family stays under the same roof and the same metallurgical control as the melt itself. Melt quality is managed through disciplined atmosphere and fluxing control, and every heat is verified rather than assumed: conductivity is tested to minimum 80 percent IACS on samples from each heat, with hardness verification and EN 10204 Type 3.1 certification from the actual production heat.

Specifying CuCrZr Investment Castings: What to Include

A complete CuCrZr specification names the grade, the condition, and the verifiable numbers - and asks for the paperwork that proves them:

Specification Item	What to State	Why It Matters
Material designation	UNS C18150 (or EN CW106C for EU procurement)	The family name alone leaves the composition range open to interpretation
Heat treatment condition	'Solution treated and aged', with target hardness or yield range	Left unspecified, an as-cast or under-aged part can be supplied and pass a dimensional check
Mechanical properties	Minimum yield strength (e.g. 400 MPa) and/or hardness range	Gives incoming inspection a verifiable acceptance number for every batch
Conductivity requirement	Minimum 80% IACS, tested on a sample from each heat	The direct proof that aging was actually performed and completed
Material certificate	EN 10204 Type 3.1 with measured values from the production heat	Real chemistry and test results, not a generic conformance declaration
Heat treatment certificate	Certificate confirming the full solution-treat-and-age sequence was completed, with the resulting hardness and conductivity test results	Documents that the full two-step sequence was performed to specification

Source CuCrZr Investment Castings from Pahwa MetalTech

Pahwa MetalTech produces investment castings - also known as lost wax castings - in CuCr and CuCrZr, solution treated and aged in-house to full specification, with conductivity verified to minimum 80 percent IACS on samples from every heat. To discuss a CuCrZr investment casting requirement, contact us or write to us at info@pahwametaltech.co.in.