The types of aluminum extrusions include:
- rods/bars (round, square, rectangle, hexagonal)
- tubes (seamless and porthole)
- profiles (solid, semi-hollow, hollow).
Extrudability is the material formability under conditions of the extrusion process. This term does not have a precise physical definition. The relative extrudability of aluminum alloys can be roughly ranked as measured by extrusion exit speed.
Some facts on extrudability:
- In general, the higher the alloy content and strength, the greater the difficulty of extrusion and the lower the extrusion rate.
- The easily extruded alloys can be economically extruded at speeds up to 100 m/min or faster.
- With a typical extrusion ratio of 40 to 1, exit speeds of the more difficult alloys are on the order of 0,6 to 1,2 m/min.
- Extrudability of the moderately difficult or very difficult alloys also cannot be significantly increased by hot extrusion technology, because of the narrow temperature interval between the extrusion load limiting temperature and the temperature of unacceptable surface quality.
- Billet temperatures generally range from approximately 300 to 595 °C , depending on the alloy.
Evaluating extrudability of aluminium alloys
To evaluate the extrudability of various aluminum profiles, the following approaches are used:
- Flow Stress
- The relative extrudability of alloys
- Complexity of an extruded shape
- The minimal wall thickness
- Limit extrusion diagram
- Tight tolerance capability of alloys
In the range 350 to 550 ⁰C, the flow stress of aluminum alloys is very dependent on the temperature and the composition [x]. The increase in the flow stress with increasing content of the most common alloying elements is shown in Fig. 1 .
The range of extrusion speeds that can be practically obtained with aluminum alloys is shown in Fig. 2. The range plotted against the flow stress at the extrusion temperatures used in practice .
Figure 3 shows the product strength of the most common aluminum alloys as a function of the flow stress at the extrusion temperature .
The extrusion load depends mainly on the flow stress kf. Thus the wrought aluminum alloys are classified according to the flow stress into the groups :
- Easy to extrude: kf less 30 N/mm2
- Moderately difficult to extrude: kf 30 to 45 N/mm2
- Hard to extrude: kf more 45 N/mm2
The flow stress of the most important extrusion alloys is shown in Table 1. The groups of aluminium alloys that differ in exrudability is shown in Table 2.
The relative extrudability of aluminium alloys
The relative extrudability of AI-alloys are shown in Table 3. Here all alloys are compared with 6063 whose extrudability index is 100. Increasing number indicates greater difficulty.
Soft, Medium and Hard aluminium alloys
R. Saha classified extrudable aluminium alloys into three different groups according to their extrudability in following way :
- Soft-grade alloys – Alloys easy to extrude:
Al, AlMn, AlMg1, 5, and AlMgSi0.8
- Medium-grade alloys – Alloys moderately difficult to extrude:
AlMg2-3, AlMgSi1, AlZnMg1
- Hard-grade alloys – Alloys difficult to extrude:
AlCuMg, AlCuMgPb, AlZnMgCu, AlMg > 3 %Mg
The relative extrudability ratings of some soft and medium-strength alloys are given in Table 4. The extrudability ratings of hard alloys are given in Table 5.
Complexity of extruded shape
The section shape is the most important factor in the extrudability considerations (Table 6). Thus, the complex shapes are extruded from 6ххх aluminium alloys. The most complex shapes are extruded from 6060 and 6063 alloys.
Two accepted methods are available for defining the complexity of an extruded shape. One method involves the use of the sha as follows [3, 4]:
This factor is a measure of the amout of surface generated per unit weight of metal citruded. The shape factor affects the production rate as well as the cost of manufacturing and maintaining the dies. It is used as a basis for pricing and provides the designer with a means of comparing the relative complexities of alternate designs .
The other measure of shape complexity is the classification of extruded shapes into different groups, based on the dificulty of extrusion (Table 6).
These approaches are based on plotting the relationship between maximum extrusion exit speeds and preheat billet temperature (Fig. 1) for a particular profile or industrial shape. The maximum exit speed (Vmax in Fig. 2), which ensures obtaining a product without surface tearing, has been frequently suggested.
An additional advantage of selecting maximum exit speed as a measure of extrudability is the fact that this parameter is both a metallurgical and productivity measurement. Flow stress and extrudability (expressed as exit speed) are plotted in Fig. 3 for several types of aluminum alloys.
Fig. 5 Limit diagram of extrusion speed, V, versus temperature
for a given extrusion load and the alloy limit for surface cracking (hot shortness) 
Minimal wall thickness
Table 7 – Relationship between minimum wall thickness, circumscribing circle
diameter (CCD), and press size for different soft- and medium-grade alloys 
To be applied only to a profiles with a specific geometry.
Similar curves may be obtained for all profiles 
extrusion force and speed, the choice of alloy, the shape of the profile,
desired surface finish and tolerance specifications 
Tight tolerance capability of alloys
Tolerance European Standard
European standards that set tolerances for extruded aluminum products are the followings:
- EN 755-3 – Round bars/rods
- EN 755-4 – Square bar/rods
- EN 755-5 – Rectangle bar/rods
- EN 755-6 – Hexagonal bar/rods
- EN 755-7 – Seamless tubes
- EN 755-8 – Porthole tubes
- EN 755-9 – Profiles
These standards distribute the alloys into two groups which correspond to varying degrees of difficulty when manufacturing the products:
- Group I – “easy-toleranced” alloys
- Group II – “difficult-toleranced” alloys
Fig. 9 – Dimension H tolerances of profiles
(The fragments of Table 2 and 3 in EN 755-9)
- Extrusion / Eds M. Bauser, G. Sauer, K. Siegert – 2nd edition, ASM International, 2006
- Extrusion of aluminium alloys / T. Sheppard
- Aluminum Extrusion Technology / P. Saha
- Aluminum and Aluminum Alloys – ASM International Handbook – 1992
- Extrusion of Aluminum Alloys /W. Misiolek, and R.M. Kelly // ASM Handbook, Volume 14A: Metalworking: Bulk Forming – 2005
- Extrusion /S. Stvren and P.Th. Moe //Encyclopedia of Aluminum and Its Alloys – Edited by G. Totten, M. Tiryakioğlu, and O. Kessler – 2019
- Sapa: Design Manual – 2007