K-factor aluminum 5052
The K-factor, or thermal conductivity, of aluminum 5052 is a critical parameter in manufacturing applications such as heat exchangers, electronic components, and cooling systems. With a typical value of 138 W/m·K (79.7 BTU/(h·ft·°F)) at 25 °C, this aluminum-magnesium alloy combines moderate heat dissipation capability with excellent corrosion resistance and formability, making it suitable for sheet metal stamping, bending, and welding processes.
Chemical Composition
Section titled “Chemical Composition”The nominal composition of alloy 5052 defines its thermal and mechanical properties. The controlled magnesium and chromium content is responsible for its conductivity and corrosion resistance.
| Element | Weight percentage |
|---|---|
| Aluminum (Al) | 97.2 % |
| Magnesium (Mg) | 2.5 % |
| Chromium (Cr) | 0.25 % |
| Max. impurities (Cu, Fe, Mn, Si, Zn) | ≤ 0.85 % total |
Thermal Properties
Section titled “Thermal Properties”The thermal parameters of aluminum 5052 determine its performance in heat transfer environments and its behavior during hot manufacturing.
| Property | Metric value | Imperial value |
|---|---|---|
| Thermal conductivity (K), 25 °C | 138 W/m·K | 79.7 BTU/(h·ft·°F) |
| Linear thermal expansion coefficient (20–100 °C) | 23.8 × 10⁻⁶ /°C | 13.2 × 10⁻⁶ /°F |
| Specific heat | 880 J/kg·K | 0.21 BTU/lb·°F |
| Melting temperature (solidus) | 607 °C / 1125 °F | 607 °C / 1125 °F |
Thermal Conductivity (K-factor)
Section titled “Thermal Conductivity (K-factor)”Thermal conductivity k quantifies how quickly heat flows through a material under a temperature gradient. It is defined by Fourier’s law for one-dimensional steady-state conduction.
q = -k · A · (ΔT / L)
| Variable | Description | Metric units | Imperial units |
|---|---|---|---|
| q | Heat flow | W | BTU/h |
| k | K-factor (thermal conductivity) | W/m·K | BTU/(h·ft·°F) |
| A | Transfer area | m² | ft² |
| ΔT / L | Temperature gradient | K/m | °F/ft |
K Values for Aluminum 5052
Section titled “K Values for Aluminum 5052”| Condition / Temper | Temperature | K (W/m·K) | K (BTU/(h·ft·°F)) |
|---|---|---|---|
| H38 (hardened) | 25 °C | 137 | 79.2 |
| O (annealed) | 25 °C | 138 | 79.7 |
| Estimated at 100 °C | 100 °C | 135 | 78.0 |
| Estimated at 200 °C | 200 °C | 130 | 75.1 |
Values above 25 °C are based on typical Al‑Mg alloy behavior, where conductivity decreases by approximately 0.05 W/m·K for each °C increase.
Operating Parameters
Section titled “Operating Parameters”In continuous thermal applications, aluminum 5052 can operate from cryogenic temperatures up to approximately 150 °C (302 °F) without significant degradation of its conductivity. Prolonged exposure above 200 °C (392 °F) may induce softening due to overaging, reducing mechanical strength without drastically affecting conductivity. Typical sheet thicknesses used in heat exchangers or heat sinks range from 0.5 mm to 3.0 mm (0.020 in to 0.118 in).
Typical Tolerances
Section titled “Typical Tolerances”Sheet dimensional tolerances influence the effective conduction thickness and the uniformity of heat flow in assembled components. Tolerances according to ASTM B209 for alloy 5052 are indicated.
| Nominal thickness (mm) | Standard tolerance (mm) | Nominal thickness (in) | Tolerance (in) |
|---|---|---|---|
| 0.5 – 0.8 | ±0.05 | 0.020 – 0.031 | ±0.002 |
| 0.8 – 1.5 | ±0.08 | 0.031 – 0.059 | ±0.003 |
| 1.5 – 3.0 | ±0.10 | 0.059 – 0.118 | ±0.004 |
Local thickness variations can alter the calculated heat flow by less than 2 % for thicknesses above 1.0 mm (0.039 in), assuming uniform contact.
Advantages
Section titled “Advantages”- Stable conductivity: the K-factor remains between 135 and 138 W/m·K (78.0–79.7 BTU/(h·ft·°F)) over the common operating range.
- Excellent marine and saline corrosion resistance, ideal for heat exchangers exposed to seawater.
- Good weldability (TIG, MIG) and cold formability, facilitating the fabrication of complex geometries.
- No post-weld heat treatment required to recover conductivity.
- High surface reflectivity when polished, reducing radiant heat absorption.
Limitations
Section titled “Limitations”- Not precipitation hardenable; the only hardening method is cold working, which can slightly reduce ductility.
- Lower conductivity than 1xxx series alloys (pure aluminum, k ≈ 220 W/m·K), so it is not optimal for applications requiring maximum dissipation.
- High-temperature service limit around 200 °C (392 °F), ruling it out for exhaust or turbine components.
- The presence of magnesium can cause stress corrosion sensitivity in aggressive environments if design is not controlled.
Selection Guide
Section titled “Selection Guide”To choose the thickness and temper of aluminum 5052 based on thermal and mechanical requirements, the following flow is recommended:
- Determine the required heat flow (Q) through thermal analysis.
- Calculate the area and thickness using Fourier’s law, with k = 138 W/m·K (79.7 BTU/(h·ft·°F)) as a starting point.
- Select the temper:
- H32 or H34 for components with some mechanical responsibility and gentle bends.
- H38 for rigid plates with maximum tensile strength (290 MPa / 42 ksi).
- O (annealed) when deep drawing or severe forming is required and structural strength is not critical.
- Verify compatibility with fluids or corrosive environments; 5052 is suitable for most industrial and marine atmospheres.
- Adjust thickness for tolerances using the tolerance table to ensure variation does not compromise the thermal gradient.
A rule of thumb for thin sheet (≤ 1 mm) in heat exchangers: prioritize H32; for structural heat sinks with stamped fins, H38 offers better thermal fatigue behavior.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the difference between the bending K-factor and the thermal K-factor in aluminum 5052?
Section titled “What is the difference between the bending K-factor and the thermal K-factor in aluminum 5052?”The bending K-factor (sheet metal) is the ratio between the neutral axis position and thickness during forming, typically between 0.33 and 0.45 for 5052. The thermal K-factor treated here is the thermal conductivity (138 W/m·K), a physical property of the material.
How does work hardening affect the thermal conductivity of 5052?
Section titled “How does work hardening affect the thermal conductivity of 5052?”The effect is minimal. The conductivity of 5052-H38 (137 W/m·K) is only 1 % lower than that of annealed O (138 W/m·K). The crystal lattice is hardly distorted to a level that significantly modifies the mean free path of electrons.
Can 5052 be used in contact with food or drinking water?
Section titled “Can 5052 be used in contact with food or drinking water?”Yes, alloy 5052 meets specifications for incidental food contact according to various international standards, although for prolonged applications evaluating the coating is recommended. Its corrosion resistance in fresh water is very good.
What is the conductivity difference between 5052 and pure aluminum 1100?
Section titled “What is the conductivity difference between 5052 and pure aluminum 1100?”Aluminum 1100 has a conductivity of approximately 220 W/m·K (127 BTU/(h·ft·°F)), 59 % higher than the 138 W/m·K of 5052. The advantage of 5052 is its superior mechanical strength and better weldability.
Does anodizing affect the surface thermal conductivity of 5052?
Section titled “Does anodizing affect the surface thermal conductivity of 5052?”The anodic layer (Al₂O₃) is a thermal insulator. A thickness of 10 µm can reduce surface transfer by less than 5 % for sheet thicknesses above 1 mm. In heat sinks, it is recommended to mask contact areas or use very thin anodizing.
What minimum thickness is recommended for heat exchangers with 5052?
Section titled “What minimum thickness is recommended for heat exchangers with 5052?”The practical minimum thickness is 0.25 mm (0.010 in) in H32 temper. Below this value, stiffness is insufficient for handling and punching may cause excessive deformation. Industrially, 0.4–0.6 mm (0.016–0.024 in) is the most common range.