How Much Do You Know About Aluminum Profile Extrusion?

01  The principle of aluminum alloy extrusion utilizes the plastic deformation properties of metals: an aluminum alloy billet heated to a softened state (typically 350-500°C) is placed into the barrel of an extruder. The billet is then forced through a heated die through a die hole, ultimately forming a profile that conforms to the cross-sectional shape of the die hole.

During this process, the aluminum alloy undergoes plastic flow and cross-sectional reshaping: metal particles within the billet migrate along the die cavity, elongating and rearranging the grains. Deformation strengthening also enhances the material's mechanical properties.

02  Common Extrusion Materials and Applications Aluminum alloys suitable for extrusion include the 2XXX series, 6XXX series, and 7XXX series. The 6 series is the most widely used due to its high cost-performance ratio.

6-series aluminum alloys (6061, 6063, 6005, 6082): Due to their Mg and Si content, they offer excellent extrusion formability, moderate strength after heat treatment (T6), and low cost. They are the most commonly used extrusion materials in new energy vehicles.

Case 1: Battery Pack Housing: Aluminum alloy extruded side beams and frames. Large structural dimensions (approximately 2 meters) require a large-tonnage extruder (≥ 5,000 tons). Common material strengths: 6061-T6 > 6005A-T6 > 6063-T6, and the extrusion process difficulty follows this gradient.

Case 2: Motor Housing: 6061 extrusion offers complex cross-sections with integrated cooling channels. 6061 also offers improved heat dissipation (thermal conductivity of 201 W/(m·K)).

Case 3: Body Structural Parts: 6082 is often used in locations requiring higher strength, such as in the body, and is reasonably priced.

7 Series Aluminum Alloy 7075: Extremely strong, but difficult to extrude (requiring higher pressure and more precise molds). Suitable for parts with stringent strength requirements, such as the aluminum alloy extrusion part (blue) used in the Audi A8, as shown below.

5 Series Aluminum Alloy 5052: Excellent corrosion resistance, but lower strength. Suitable for low-stress, high-corrosion-resistance applications, particularly in the construction industry.

03 Difficulties in Extrusion Processing

Mold design and manufacturing for complex cross-section molds require precise calculation of metal flow velocity to avoid localized cracking caused by excessively fast flow (e.g., in thin-walled areas) or insufficient filling caused by excessively slow flow. Mold machining accuracy must reach ±0.01mm, which is costly.

Dimensional accuracy control is affected by material thermal expansion and contraction and extrusion speed fluctuations. Parts are prone to dimensional deviation (e.g., straightness errors exceeding 0.5mm/m), requiring correction through stretch straightening and subsequent processing.

Surface quality issues may include defects such as scratches, residual scale, and bubbles. Strict control of billet surface quality and mold finish (Ra ≤ 0.8μm) is required.

Extrusion of large parts, such as battery pack casings for new energy vehicles (over 2m in length), requires a high-tonnage extruder (≥ 5000 tons) and is prone to deformation due to uneven metal flow.

04 Design Features of Extruded Parts

Extrusion Dimensions

Extrusion part dimensions are determined by the minimum cross-sectional diameter (CCD). The following example shows a structural optimization to reduce CCD. The CCD should be minimized. Avoid Asymmetric Structures

Symmetrical and Simple Cross-Sectional Structures: Asymmetric and unbalanced cross-sections increase the complexity of extrusion production and are prone to quality issues: dimensional accuracy and flatness are difficult to maintain, part warping occurs at the center, production efficiency is low, and mold wear is increased during large-scale production.

Wall Thickness

The wall thickness of an extruded part is related to the material, shape, and its circumscribed circle diameter (CCD). The extrusion shape also influences the wall thickness design. In the figure below, red represents a tubular structure, and blue represents a non-tubular structure. As the CCD increases, the optimal wall thickness also increases.

Tolerance Matching

The assembly tolerance with other parts (such as battery modules) must be ≥0.1mm to avoid assembly difficulties caused by extrusion dimensional fluctuations. Furthermore, part thickness tolerances should consider performance and retain design margins.

05 Mechanical Properties of Extruded Aluminum Alloys

Do the material properties of aluminum alloy parts change after the extrusion process? Do they weaken or strengthen? How should material properties be determined during the design process?

Generally, extrusion processes improve strength through grain refinement and work hardening, while plastic deformation increases dislocation density and decreases elongation. The specific performance changes of extruded materials depend on parameters such as extrusion pressure, temperature, and speed. Even the aging treatment of extruded parts can affect performance. Therefore, actual testing is required for reliable results. In the early stages of design, appropriate reference to raw material properties should be made and sufficient design margins should be retained.