Lean chemistry
Keep Mg and Si close to the stoichiometric Mg2Si ratio, with Cu, Mn and Cr as low as practical. Each 0.1 % of manganese in solution costs measurable conductivity.
Thermal-structural sheet guide
High-Strength 6000 Series Aluminium Sheet for Structural Thermal Parts
Battery packs, inverters, power modules and telecom units increasingly ask one aluminium part to be both a structure and a heat sink. Within the 6000 series there is a direct trade-off: alloying and ageing that raise strength also lower thermal conductivity. This guide explains that trade-off, compares 6061, 6063, 6060 and 6101 sheet, and shows how alloy lean-ness and temper can be tuned to hit a target such as at least 200 MPa tensile strength with at least 180 W/m·K.
- Alloy family
- Al-Mg-Si (6xxx)
- Conductivity range
- about 165 – 220 W/m·K
- Thickness
- from about 0.2 mm
- Uses
- EV, power electronics, telecom
Why strength and conductivity pull in opposite directions
Heat and electricity travel through aluminium mainly by free electrons. Anything that disturbs the regular crystal lattice scatters those electrons and lowers conductivity. Atoms dissolved in the aluminium (solid solution) scatter strongly; atoms gathered into precipitates scatter much less.
That explains the behaviour of 6xxx alloys. In the solution-treated T4 condition, magnesium and silicon are dissolved and conductivity is at its lowest. Artificial ageing pulls them out into fine Mg2Si precipitates, which both strengthens the alloy and raises conductivity. Ageing further (over-ageing, the T7 tempers) coarsens the precipitates, clears more solute from the matrix and raises conductivity again, but strength now falls.
Alloying elements that stay in solution are the biggest penalty. Copper, manganese, chromium and excess iron or silicon all reduce conductivity noticeably, which is why 6061 (with copper and chromium) conducts less heat than lean 6063 or 6101. A structural thermal grade is therefore designed lean: just enough magnesium and silicon to reach the strength target, minimal transition elements, and an ageing practice chosen for the balance point.
Common 6xxx sheet grades compared
| Grade and temper | Typical yield strength | Typical tensile strength | Thermal conductivity | Leans towards |
|---|---|---|---|---|
| 6061-T6 | 276 MPa | 310 MPa | about 167 W/m·K | Structure |
| 6005A-T6 | about 240 – 260 MPa | about 270 – 290 MPa | about 180 – 190 W/m·K | Structure, extrusions |
| 6063-T6 | 214 MPa | 241 MPa | about 200 W/m·K | Forming and finish |
| 6060-T6 | about 150 – 190 MPa | about 190 – 220 MPa | about 200 – 210 W/m·K | Extrusion and conductivity |
| 6101-T6 / T63 | about 170 – 195 MPa | about 200 – 220 MPa | about 210 – 220 W/m·K | Electrical / thermal conduction |
| 1050-H14 (reference) | about 105 MPa | about 115 MPa | about 229 W/m·K | Conduction only |
Typical values from Aluminum Association and ASM data; sheet values vary with thickness and the exact ageing practice. Conductivity is usually verified by measuring electrical conductivity (% IACS) and converting with the Wiedemann–Franz relationship.
A common brief for thermal-structural parts reads "tensile strength at least 200 MPa and thermal conductivity at least 180 W/m·K". 6061-T6 meets the strength easily but misses the conductivity; 1xxx sheet misses the strength. Lean 6xxx alloys in a tuned peak-aged or slightly over-aged condition hit both, and that is the zone to aim for.
How the balance is tuned
Iron control
Iron forms intermetallic particles rather than staying in solution, so modest iron is tolerable; it improves grain control in thin sheet.
Peak or over-ageing
Peak ageing (T6) gives maximum strength. A short over-age (T7-type or T63/T64 practices used for 6101) raises conductivity by a few per cent for a modest strength loss.
Cold work after ageing
A small final rolling reduction (T8- or T9-type tempers) adds strength with little conductivity penalty, useful in very thin sheet.
Thickness
Thin sheet (0.2 – 1 mm) is quenched quickly and uniformly, so properties are consistent through the gauge.
Verification
Order with both a mechanical and a conductivity requirement, and ask for conductivity results per lot.
Where structural thermal sheet is used
| Sector | Typical parts | Why both properties matter |
|---|---|---|
| Electric vehicles | Inverter and motor-controller housings, IGBT base plates, battery cooling plates and module supports | Parts carry mounting and crash loads while moving heat to coolant |
| Energy storage and solar | PCS converter frames, power-module heat sink bases | Long duty cycles at high power density |
| Telecom and 5G | Radio-unit housings, power-module brackets | Fanless outdoor units rely on conduction through the structure |
| Data centres | Server power-supply frames, high-power module plates | Compact layouts with high heat flux |
| Industrial electronics | Converter frames, load-bearing heat sinks | Combines enclosure and cooling functions |
Forming, joining and finishing
- Forming: lean 6xxx sheet forms well in T4; bend or draw before ageing where possible, then age to the final temper.
- Joining: welding and brazing heat soften the aged structure; mechanical fastening, adhesive bonding and friction-stir welding preserve properties better.
- Anodising: 6063-type chemistries give the most even appearance. A thin anodic film adds electrical insulation but slightly reduces surface heat transfer, so specify it deliberately.
- Thermal interfaces: flatness and surface finish affect contact resistance as much as alloy choice; ask for flatness limits on base plates.
What to specify when ordering
- Property targetsMinimum tensile and yield strength, minimum thermal or electrical conductivity, and elongation if the part is formed.
- DimensionsThickness (from about 0.2 mm), width, coil or sheet length and tolerances.
- TemperT4 for forming then ageing, or a fully aged temper for flat parts.
- TestingTensile tests and conductivity measurement per lot, reported on an EN 10204 3.1 certificate.
- Finish and packingSurface quality, protective film, interleaving and export packing.
References and standards
- ASTM B209 – Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate
- EN 485-2 – Aluminium and aluminium alloys: sheet, strip and plate, mechanical properties
- ASM Handbook, Vol. 2 – Properties and Selection: Nonferrous Alloys and Special-Purpose Materials
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
- ASTM E1004 – Standard Test Method for Determining Electrical Conductivity Using the Electromagnetic (Eddy Current) Method
Structural thermal 6000 series sheet: FAQ
Which 6000 series aluminum has the highest thermal conductivity?
6101 in an aged temper, at about 210 – 220 W/m·K, followed by 6060 and 6063 at around 200 W/m·K. 6061 is lower, about 167 W/m·K, because of its copper and chromium.
Can 6063 replace 6061 for a heat-sink structure?
Often, if the loads allow. 6063-T6 conducts about 20 % more heat but has roughly 20 – 25 % lower yield strength. Check stiffness and strength margins first.
How can sheet reach 200 MPa tensile and 180 W/m·K at the same time?
Use a lean Al-Mg-Si chemistry with low copper, manganese and chromium, aged to peak or slightly over-aged. Specify both properties on the order and require conductivity test results.
How is thermal conductivity checked on production sheet?
Usually by measuring electrical conductivity with an eddy-current meter and converting it, because the two are closely related in aluminium. Direct thermal measurement is used for qualification.
What is the thinnest sheet available?
Lean 6xxx sheet can be supplied from about 0.2 mm, in coil or cut sheets, with thickness tolerance agreed per order.
Designing a part that must carry load and shed heat?
Send your strength and conductivity targets with thickness and quantity. Metline will suggest grades and tempers and quote worldwide.
