T4
Solution treated, quenched and naturally aged. Formable, but continues to age slowly at room temperature, so press performance changes with storage time.
Automotive materials guide
Auto Body Aluminium Panel Sheet
Auto body aluminium sheet is rolled 5xxx and 6xxx alloy sheet made for car body panels: bonnets, doors, roofs, wings, boot lids and the inner panels and structure behind them. Outer panels use bake-hardenable 6xxx alloys that form well in T4 and gain strength in the paint oven; inner and structural parts often use non-heat-treatable 5xxx alloys. This guide explains which alloy goes where, the tempers and surfaces involved, and how to specify sheet for a body programme.
- Outer panels
- 6016, 6111, 6014, 6022
- Inner panels
- 5182, 5754, 6xxx
- Tempers
- T4, T4P, O, H111
- Typical gauge
- about 0.8 – 3 mm
Why aluminium is used for car body panels
An aluminium body panel weighs roughly half as much as a steel panel of equivalent stiffness and dent resistance, because the thinner-but-lighter steel sheet is replaced by a somewhat thicker aluminium sheet with one third of the density. On closures alone (bonnet, doors, boot lid, wings) the saving is typically tens of kilograms per vehicle, which improves range, handling and emissions.
Aluminium was first used widely on bonnets and boot lids and is now common on doors, roofs and complete bodies in white. Electric vehicles have accelerated the trend: every kilogram saved in the body offsets battery mass and extends range.
Body sheet is not ordinary commercial sheet. It must form into deep, sharp-featured shapes without splitting, hem tightly around inner panels, show no surface defects under glossy paint, bond and weld consistently, and respond predictably to the paint-bake cycle. That is why body sheet is produced to OEM specifications with tight control of chemistry, texture, surface and ageing.
Which alloys are used for which body parts
| Component | Common alloys | Why |
|---|---|---|
| Outer panels: bonnet, doors, roof, wings, boot lid | 6016 (Europe), 6111 and 6022 (North America), 6014, 6451 | Good formability in T4, strength gain in the paint oven for dent resistance, clean Class A surface without stretcher marks |
| Inner panels: bonnet and door inners, boot inner | 5182, 5754, 6016, 6014 | High formability for deep draws; 5xxx surfaces are hidden, so stretcher marks do not matter |
| Structural parts: pillars, sills, floor, reinforcements | 5754, 5182, 6xxx high-strength grades | Strength, crash performance and corrosion resistance |
| Wheel arches, mudguards, splash shields | 5754, 5182 | Corrosion resistance and formability in exposed underbody zones |
| Battery enclosures and trays | 5754, 6061, 6082 sheet with extrusions | Strength, weldability and crash protection; see the EV battery tray guide |
| Heat shields | 1050, 3003 embossed sheet | Reflectivity and formability |
2xxx alloys such as 2036 were used on outer panels in the 1970s and 1980s but were displaced by 6xxx alloys, which have better corrosion resistance, recyclability and paint-bake response. Some older component lists still mention them.
Alloy choices vary between OEMs and regions. Always follow the vehicle maker's material specification.
T4, T4P and the paint-bake response
6xxx body sheet is delivered in a solution heat-treated and naturally aged temper (T4) in which it is relatively soft and formable. After stamping and assembly the body passes through the paint-curing oven, typically around 170 – 185 °C for about 20 – 30 minutes, which artificially ages the alloy and raises its yield strength. This "bake hardening" gives dent resistance without sacrificing formability at the press.
T4P (pre-aged)
Given a short pre-ageing treatment straight after quenching. This stabilises the sheet and strengthens the paint-bake response, so a short, cool oven still delivers good final strength.
O / H111 (5xxx)
Annealed 5182 and 5754 for maximum formability in inner and structural parts. Strength comes from magnesium in solid solution and work hardening during forming; there is no paint-bake gain.
| Alloy and temper | Typical behaviour |
|---|---|
| 6016-T4 / T4P | Low yield as delivered for good hemming and formability; yield roughly doubles after pre-strain and paint bake, typically reaching around 200 MPa |
| 6111-T4 | Higher strength as delivered and after bake than 6016, for thinner, dent-resistant outer panels; slightly lower formability and hemming performance |
| 5182-O | High formability and strength among non-heat-treatable alloys; tensile strength about 255 – 315 MPa (EN 485-2 range) |
| 5754-O | Good formability and corrosion resistance, lower strength than 5182; tensile strength about 190 – 240 MPa (EN 485-2 range) |
Indicative values. Specified limits depend on thickness and on the OEM specification; actual results are reported on the mill certificate.
Sizes, surfaces and processing
Typical supply range
- Alloys
- 5xxx: 5182, 5754, 5052, 5083; 6xxx: 6016, 6111, 6014, 6022, 6061
- Tempers
- O, H111, H32, T4, T4P, T6
- Thickness
- About 0.8 – 3 mm for body panels; thinner and thicker sheet and plate for other parts
- Width
- Up to about 2000 mm and wider on request for one-piece side and roof panels
- Form
- Coil, cut-to-length sheet and blanks (rectangular or shaped)
- Surface texture
- Mill finish (MF) or electro-discharge textured (EDT) for better lubricant retention and paint appearance
- Surface treatment
- Titanium/zirconium conversion pretreatment for adhesive bonding; dry-film lubricant or pre-lube oil
Blanks can be cut rectangular or to trapezoidal and curved outlines to reduce scrap at the press. Tell us whether you need coil, sheet or blanks, and the lubricant and pretreatment your press shop and paint line accept.
Forming, hemming and joining body sheet
Stamping
Aluminium has lower formability than mild steel and springs back more. Generous radii, optimised draw beads, good lubrication and simulation with correct material data are essential.
Hemming
Outer panels are folded 180° around inner panels. Alloys and tempers for outer panels are chosen to hem flat without cracking; 6016 in T4 and T4P hems well.
Stretcher strains
5xxx alloys can show Lüders lines (stretcher-strain marks) after forming, which show through paint. That is why 5xxx is kept to hidden inner and structural parts.
Joining
Self-piercing rivets, clinching and structural adhesive are the main methods; resistance spot welding, laser welding and flow-drill screws are also used. Pretreated surfaces give durable bonds.
Mixed materials
Where aluminium meets steel or carbon fibre, adhesive, sealer or coatings isolate the materials to prevent galvanic corrosion.
Storage
T4 sheet ages at room temperature, so press shops use stock in order of production and within the shelf life given by the specification.
Brazing sheet for automotive heat exchangers
Besides body panels, cars use large amounts of clad aluminium brazing sheet in radiators, condensers, evaporators, heater cores, oil coolers, intercoolers and battery cooling plates. A 3xxx core is clad with a 4xxx brazing alloy that melts in the furnace, and often with a zinc-bearing 7072 layer that protects the core sacrificially.
| Part | Typical materials |
|---|---|
| Radiator and heater tubes | 4045 or 4343 / 3003 (or long-life core) / 7072 clad strip |
| Fins | 3003, 3003 + Zn, 7072-type alloys and other fin stock |
| Oil coolers | 6951 or 3xxx cores clad with 4xxx alloys |
| Intercoolers | Clad tube stock with 1100, 3003 or 3005 fins |
| Battery cooling plates | Clad 3xxx brazing sheet and plate |
See the brazing sheet for automobiles guide for clad ratios, brazing processes and alloy combinations.
How to source auto body sheet from Metline
- SpecificationAlloy, temper, thickness, width and the OEM or Tier-1 material specification, plus EN 485, EN 573-3 or ASTM B209 where applicable.
- Form and surfaceCoil, sheet or blanks; MF or EDT texture; pretreatment and lubricant.
- Samples and approvalTrial coils or sheets for press and paint trials before series supply.
- DocumentsMill test certificate to EN 10204 3.1 with chemistry and mechanical properties; additional tests on request.
- LogisticsEye-to-sky or eye-to-wall coil packing, moisture protection and delivery on EXW, FOB, CIF or DAP terms.
Metline also supplies the extrusions, forgings and plate used elsewhere in the body and chassis, so a lightweighting project can source its aluminium from one partner.
References and standards
- EN 485-2 – Aluminium and aluminium alloys: sheet, strip and plate, mechanical properties
- EN 573-3 – Aluminium and aluminium alloys: chemical composition and form of wrought products
- ASTM B209 – Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate
- European Aluminium – Aluminium Automotive Manual
- The Aluminum Association – Aluminum in transportation
Auto body aluminium (aluminum) sheet: FAQs
Which aluminium alloy is used for car body outer panels?
6xxx bake-hardenable alloys: mainly 6016 in Europe and 6111 or 6022 in North America, with 6014 and 6451 also used. They form well in T4 and gain strength in the paint oven.
Why is 5182 not used for outer panels?
5xxx alloys can develop stretcher-strain marks during forming that show through paint, and they do not bake harden. They are excellent for inner and structural panels where the surface is hidden.
What is the difference between T4 and T4P?
Both are solution treated and naturally aged. T4P adds a pre-ageing step after quenching that stabilises the sheet during storage and gives a stronger response in the paint-bake oven.
How much weight does an aluminium bonnet save?
Typically around 40 – 50 % compared with an equivalent steel bonnet, because the aluminium sheet is slightly thicker but has one third of the density.
How are aluminium body panels joined?
Mainly with self-piercing rivets, clinching and structural adhesives, plus resistance spot and laser welding. Outer panels are hemmed around inner panels.
Does Metline make body panels?
No. Metline supplies the aluminium sheet, coil and blanks that stamping plants and body manufacturers form into panels, together with mill certificates.
Sourcing aluminium for a body programme?
Send the alloy, temper, gauge, width, surface and specification. We will reply with availability, documents and a delivered price.
