Manufacturers who work with metal know that one of the most important considerations of selecting a material is how strong it is. Factors such as strength, hardness, durability and toughness all make a difference to the quality of the final product. That’s why we are constantly getting questions about the strength of various alloys. That includes inquiries into whether or not bending metal can make it stronger.
In today’s post, we’ll look at that question and explain the mechanics behind bending aluminum and stainless steel as well as how it affects the overall strength of the material. It’s important to note that every alloy reacts differently. Before making a final selection of what material is best for any given operation, you should thoroughly test and prototype your product to make sure that it behaves in the desired manner, especially with regards to its overall strength and durability. Theory does not always translate into practice!
What is ductility?
When talking about bending metal, it’s critical to understand ductility. Ductility is defined as a measure of how much a material can be deformed before it reaches a breaking point. In mechanical engineering, ductility can be represented as a percent elongation or percent area reduction based on a tensile test. Another way of expressing ductility is by the material’s ability to be drawn into a wire. For example, one ounce of gold can be stretched into 80 km of gold wire, an indication of gold’s high ductility.
In metalworking, ductility is frequently an important consideration. Because metals must often be shaped through various means such as forging, rolling, extruding or drawing, it is necessary to know whether the metal will break or otherwise become deformed under stress. Metals with a high ductility have, at the molecular level, delocalized electrons that can be shared among many atoms. Thus, when subjected to strong forces, a ductile metal’s atoms can slide past each other without causing rupture.
A typical ductility test involves taking a metal rod and clamping it down at either end, then pulling it apart. The nature of the break indicates how ductile a metal is. A brittle alloy will break without much stretching and have a very rough break surface, whereas a ductile metal will be drawn apart and have an elongated, bullet-shaped break. In the most extreme cases, the metal will be stretched into wire, as with gold mentioned above.
The most ductile known metal is platinum.
How does bending affect metals like aluminum and stainless steel?
Now, with that out of the way, let’s look back at the original question, does bending metal make it stronger? The answer is: that depends. That might shock many people who aren’t familiar with one of the key properties of many metals, which is that certain types of metal alloys can undergo what is known as work hardening. This means when forces such as bending, squeezing or drawing are applied to a metal it is strengthened rather than weakened. This is why in the example used above of stretching gold into wire that the material does not break immediately. As the two ends are drawn apart, the metal actually hardens.
Work hardening affects different metal alloys in different ways. The general principle is as follows: when the pressure is applied at first, a deformation forms in the metal. As the force continues and more deformation occurs, rather than weaken the metal, it strengthens it. This is due to its crystalline structure. As the crystal deformations increase, the structure becomes more complex and less slippage can occur. Along with hardening, the metal is also losing some of its ductility, so while the metal is stronger, it has a higher likelihood of fracture if enough force is applied.
As a practical example: when you take a paper clip and try and bend it back and forth until it breaks, this is a demonstration of work hardening. It may intuitively seem like you are weakening the material, but it’s becoming stronger. As you continue to bend it, it becomes more resistant to the pressure you are applying. If enough force is applied, it will eventually break into two pieces.
Stainless steel alloys can be work hardened, but austenitic stainless steel can be hardened quickly. In fact, the 300 series of austenitic stainless steels can ONLY be cold worked, meaning that heat treatment will not work with them. Other steels can be hardened by either cold working or heat treatment.
As for aluminum, which is generally considered more formable, bending and other work hardening methods are even more effective. Each alloy reacts differently to bending, and some are more receptive than others. Alloys such as those in the 3xxx and 5xxx series are prime candidates for bending applications. 2xxx and 7xxx series aluminums are already naturally very strong and less formable. As for the 6xxx series, some alloys such as 6063 are good for bending, while others, such as 6082, are not.
When you are bending any kind of metal, whether it’s pipe, bar, sheet or some other shape, it’s important to realize that you will need to over-bend the work piece, because once the pressure is released some amount of bend back will take place. The amount of bend back depends on the alloy.
Your technical services provider
Stainless steel and aluminum are prized for both their strength and formability. Being able to shape the metal while retaining, or in some cases, increasing its strength, makes these materials extremely versatile and perfect for all kinds of industrial applications. Naturally, before you begin production, it’s important to carefully test and prototype your application to ensure its viability.
This is where the help of a seasoned metal supplier can be invaluable. At Clinton Aluminum, we pride ourselves on our ability to work with our clients at every step of the supply stream. Our professional team is committed to supporting our clients to achieve success.
If you have a question about bending aluminum or stainless steel, contact us today to speak with one of our knowledgeable and friendly sales professionals.