EN
C18070 Properties: Conductivity, Strength, Bendability and Two High-Temperature Behaviours
The first article introduced C18070 as a high-conductivity copper-chromium-silicon-titanium alloy. Its value lies in a balance of properties rather than a single peak, so this article sets them out — and clears up a distinction that causes more selection errors than any other.
Mechanical properties by temper
The R-tempers are named by minimum tensile strength in MPa. Ranges reflect normal production spread; a mill certificate states the measured values for your lot.
Temper |
Tensile Rm MPa (ksi) |
Yield Rp0.2 MPa (ksi) |
Elong. A50 (%) |
Hardness HV |
R400 |
400 – 480 (58 – 70) |
≥ 300 (≥ 44) |
≥ 9 |
120 – 150 |
R460 |
460 – 560 (67 – 81) |
≥ 400 (≥ 58) |
≥ 9 |
140 – 170 |
R540 |
540 – 620 (78 – 90) |
≥ 460 (≥ 67) |
≥ 8 |
150 – 190 |
R580 |
580 – 650 (84 – 94) |
≥ 520 (≥ 75) |
≥ 7 |
150 – 190 |
Strength and hardness rise from R400 to R580 while elongation eases down. This is a medium-strength alloy by design: it is not trying to match a spring alloy's peak, because doing so would cost conductivity and bendability. The point is to have enough strength while keeping the other two properties high.
Bendability
This is where C18070 stands apart from most conductive alloys. Tested at 90° with thickness ≤ 0.5 mm, the minimum bend ratios are:
Temper |
Good way (× t) |
Bad way (× t) |
R400 |
0 |
0 |
R460 |
0.5 |
0.5 |
R540 |
1 |
1 |
R580 |
1 |
1.5 |
In the R400 condition the alloy achieves a 0t bend both good-way and bad-way — it can be folded flat on itself without cracking. That allows genuinely complex stamped and formed shapes in a material that still conducts at over 78% IACS. As temper hardens, the required radius grows, so complex geometry favours the softer tempers. State both the bend radius and its orientation on the drawing so the right temper is supplied.
The two high-temperature behaviours — do not confuse them
Buyers often ask for "good high-temperature performance" as if it were one property. It is two, driven by different mechanisms, and a part can need one, the other, or both:
Stress relaxation resistance — whether a part under sustained load keeps its contact pressure, or gradually loosens. This is the property a connector relies on to keep gripping over years at temperature.
Softening resistance — whether the material itself loses strength and goes soft when heated. This governs whether the part holds its shape and hardness after a hot excursion.
C18070 performs well on both, but they answer different questions. If the part's failure mode is "the contact goes loose after months in service," the relevant figure is stress relaxation. If it is "the part softens after a heat exposure," the relevant property is softening resistance. Specifying against the wrong one is a common and expensive mistake.
Stress relaxation figure
Under 200°C for 1000 hours, C18070 retains at least 85% of its stress. In service terms, a contact keeps the large majority of its clamping force after long, hot operation — the behaviour a high-voltage battery or under-hood connector depends on. Combined with 78–83% IACS conductivity, this is the pairing that makes the alloy suit high-current connections that also run hot.
Frequently asked questions
Which temper gives the best bendability?
R400, which can achieve a 0t bend both good-way and bad-way, making it suited to complex formed parts.
What is the stress retention of C18070 at high temperature?
At least 85% after 200°C for 1000 hours, indicating stable contact force over long hot service.
Is stress relaxation the same as softening?
No. Stress relaxation is loss of contact force under sustained load; softening is loss of material strength on heating. They are separate mechanisms and should be specified separately.
Next in this series: C18070 Applications — EV battery connectors, photovoltaic hardware, relays and fuse boxes.