“Which aluminum alloy bends the best?” is a a common question customers want the answer to. In this post, we’ll explain it to you.
BACKGROUND
In high purity forms, aluminum is soft and ductile. Bending is a delicate and demanding process most of the time and common fabricating processes require a degree of formability that make your choice of proper alloy critical.
Depending on designation, alloys go through different heat treatment procedures during production. Typically, pure aluminum is more easily worked than the alloys. Annealed and natural aged tempers are more easily worked than hard tempers and artificially aged ones.
But the question remains the same – which alloy is the best product for bending? There are three factors that contribute to the the answer.
FACTOR 1 – FORMABILITY
To understand this better, we need to talk about alloys, which is the first factor to consider upon selection. In aluminum, we have various designations that all have different chemical compositions, making them applicable in various fields of metal processing. The most important ones are:
Series 1xxx are the Aluminum alloys with 99.00% pure aluminum. They have little structural value. They are very ductile in the annealed condition and have excellent corrosion resistance.
Series 2xxx are the Aluminum – Copper alloys. These alloys have excellent machinability, limited cold formability (except in the annealed condition) and less corrosion resistance than other alloys, which is why they are anodized prior to usage.
Series 3xxx are the Aluminum – Manganese alloys. With an addition of 1% Manganese, these alloys have no significant loss in ductility, good corrosion resistance, and very good formability. This series is one of the most preferable for forming applications.
Series 4xxx are the Aluminum – Silicon alloys. This series has the addition of silicon, thus lowering the melting point and for this reason, it is used entirely for manufacturing welding wire.
Series 5xxx are the Aluminum – Magnesium alloys. They exhibit a very good combination of high strength, resistance to corrosion, formability, and good weldability.
Series 6xxx are the Aluminum – Magnesium – Silicon alloys. These heat treatable alloys exhibit great strength, good corrosion resistance, and ease of formability. The are mainly used in architectural applications.
Series 7xxx are the Aluminum – Zinc – Magnesium and Aluminum – Zinc – Copper alloys. They exhibit very high strength, making them very difficult to form.
So, we see that specific alloys have a high degree of formability that provide the proper behaviour in processing and especially in bending.
FACTOR 2 – THICKNESS AND BEND RADIUS
Another factor to consider is that during the process of bending, the metal hardens and strengthens by reason of the working effect. Apart from alloy selection, thickness and bend radius are also critical factors that must be considered. The table below shows the permitted bend radii for 90o bending.
Source: https://www.aircraftspruce.com/pdf/2015Individual/Cat15056.pdf
FACTOR 3 – PERCENTAGE OF ELONGATION
A third factor to be considered is that formability of a specific alloy can be found in the percentage of elongation and the difference between yield strength and ultimate tensile strength.
This rule states that the higher the elongation value (the wider the range between yield and tensile strength), the better the forming ability of the alloy.
From the aforementioned descriptions of alloys and the data shown in table 3 (below), it is quite obvious that the best series for forming, and thus for bending, are series 3xxx, 5xxx, and in some cases 6xxx. Series 2xxx and 7xxx are not to be considered and thus should be avoided due to being extremely strong. They are difficult to form in any way.
Top 3 Aluminum Alloys For Bending
1. 3003. This would be the best solution for most application. This alloy exhibits medium strength, the best cold workability together with high elongation such as 25% and one of the biggest differences between yield and tensile strength of 14 Ksi (Kilo-pound of force per square inch) at 0 temper – annealed, followed by the H14 temper which is partially annealed and strain hardened.
2. 5052. 5052 is a close second. At the annealed temper, it has an elongation of 20% and the difference between yield and tensile strength of 21.5 Ksi. It is the highest strength alloy of the more common non-heat treatable grades. It has excellent corrosion behavior and in the annealed condition has better formability than 3003 or even 1100 alloys, with 21.5 Ksi of difference between yield and tensile strength and up to 20% of elongation.
3. 6061. This is one of the most versatile of the heat treatable family of alloys. In the annealed condition, it can be used for bending since the difference between yield and tensile strength is 10 Ksi and elongation is up to 18%. When moving up to T4 and T6 tempers, however, bending ability tends to decrease. Bending these temered alloys is not impossible, but requires great caution and probably larger bending radii to avoid cracking.
7005 and 2024 alloys are not recommended for bending, since they are both alloys with great strength and forming capabilities which are very limited even in annealed condition.
Aside from these, special products such as ATP-5, K100-S, Duramold-2, Duramold-CS and M-1 are not recommended for bending applications. Table_3 below shows characteristics of the alloys discussed previously.
Source: https://www.aircraftspruce.com/pdf/2015Individual/Cat15056.pdf
Appendix_A
Calculation of maximum bending force:
Where,
F=bending force
TS = Tensile Strength of sheet metal
W = part width in direction of bend axis
T = stock thickness
Kbf = 1,33 for V-bending
Kbf = 0,33 for edge bending
References:
https://www.practicalmachinist.com/vb/general/aluminum-alloy-best-bending-using-thin-sheet-267073/
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