## What Is Thermal Conductivity?
Thermal conductivity (k) is the rate of heat flow per unit area per unit temperature gradient, in W/(m-K). Fourier's law: Q = -k x A x (dT/dx).
## Values for Common Metals
| Metal/Alloy | k at 25 degrees C (W/m-K) |
|------------|---------------------------|
| Silver | 429 |
| Copper (C11000) | 391 |
| Aluminum (1100) | 222 |
| Aluminum (6061-T6) | 167 |
| Carbon steel (1018) | 51 |
| 304 Stainless | 16 |
| Titanium (Grade 2) | 16 |
| Inconel 625 | 9.8 |
## Why Alloying Reduces Conductivity
Heat is carried by free electrons in a regular lattice. Alloying disrupts periodicity, scattering electrons. Pure copper: 391 W/m-K. Cupronickel (70Cu-30Ni): 29 W/m-K (93% reduction).
## The Wiedemann-Franz Law
Thermal and electrical conductivity are proportional in metals (k/sigma = L x T) because both are carried by free electrons.
## Engineering Applications
**Heat exchangers**: Fluid-side resistance usually dominates. A 316L tube (k=16) has only 5-10% worse overall U than copper (k=391) in turbulent flow.
**Heat sinks**: Aluminum 6063 (k=201) dominates due to conductivity + low density + extrudability. Copper for high-power-density applications.
**Welding**: High conductivity (copper, aluminum) dissipates heat rapidly, requiring higher heat input. Low conductivity (stainless, titanium) concentrates heat, enabling deep penetration but increasing distortion.
**Thermal stress**: Low thermal conductivity materials develop steeper temperature gradients, increasing susceptibility to thermal shock and fatigue.
Thermal Conductivity in Metals and Alloys
Thermal conductivity determines how efficiently heat flows through a metal, governing heat exchanger performance, heat sink design, welding behavior, and thermal management in electronics and engines.
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