A Brief Look At Aluminum Tube Products

For most people, the term “tube” brings to mind a long, cylindrical shaped object. And the round tube shape is typically the configuration of tubing. In the aerospace industry, however, metal tubing can also be square or rectangular.

The tube shape, specifications and composition all factor in to how and the tube material, or part, is used.

Tube Construction Basics

It’s important to keep in mind that when referring to or ordering tube material that there are a few basic measurements, or specifications that are critical.

• O.D. – outside diameter
• I.D. – inside diameter
• Wall thickness

Because all tubes, regardless of their shape, have two walls these combine with the inner diameter to provide the overall outside diameter measurement.

When ordering aluminum tube parts there are specific nomenclature assigned to part numbers. 

• Round tube: e.g. 2024-T3 TUBE 2.00 X .125
• Square tube: e.g. 7075-T6 TUBE 1SQ X .049
• Rectangular tube: 6061-T6 TUBE 4.00 X 8.00 RECT (Note that the wall thickness is not listed.)

Metal tubing is available in many other materials in addition to aluminum. These include steel, titanium, brass/copper, stainless steel, as well as various alloys and carbon fiber composite materials. 

And, depending on the primary metal, the materials can be produced in various types such as:

• Drawn
• Extruded
• Welded
• Seamless
• Hydraulic
• Structural pipe

Tube Talk

When it comes using metal parts in fabrication, manufacturing and construction, tensile strength is often a critical factor. Metal tubing is no exception. 

So, how strong is aluminum tube?

The answer is dependent on several factors such as diameter, wall thickness, alloy and finish. A straight comparison to another common product, steel tube, can provide some context, however.

According to an entry at Sciencing.com, 

“The strength of any material can be described by a physical parameter known as Young’s modulus of elasticity, measured in force per unit area. This parameter can be used to assess the strength of aluminum and steel tubing.

At 70 degrees Fahrenheit, Young’s modulus of elasticity for aluminum is 10 million pounds per square inch (psi). Young’s modulus of elasticity for steel, regardless of its type, is around 30 million psi. This effectively means that steel tubing is three times stronger than aluminum tubing of the same dimensions.”

However, a length of steel tube is about three times heavier than an aluminum tube of the same length and dimensions. In order for that aluminum tube to have the same bending strength as its steel counterpart the walls of the aluminum tubing would need to be three times thicker than the steel tubing. This would remove any weight advantage typically looked for in using aluminum parts.

When it comes to aluminum tube, shape is also a determining factor in overall strength. For example, round tube is stronger than square tube of an equal length and weight, In addition, round tube has a higher resistance to both flex and torsional twisting than square tube for a given weight.

Applications of Aluminum Tube

Aluminum tube is used in a variety of industries and by hobbyists, for various DIY projects and assorted manufacturing and construction fields. In addition, it is extensively used in the aerospace industry. 

A good example is 6061-T6 aluminum tubing that is a commonly used in the aircraft/aerospace industry because of its strength, weldability, and ease of machining. Most all aluminum tubing can be furnace brazed and welded by all types of welding.

Aluminum and aluminum alloys are the most commonly used metals in the aerospace industry for a variety of reasons. Its relatively low cost, light-weight, and machinability are among the primary reasons for its widespread use.

Aluminum is non-sparking, non-magnetic, electrically and thermally conductive, and chemically resistant. In addition to the aircraft industry, it is also popular in construction and marine applications due to its ease of fabrication, non-toxicity, strength, and corrosion resistance in industrial and marine environments.

Anodizing aluminum increases its corrosion resistant properties and allows for iridescent finishes in a variety of colors. Because some alloys can be slightly corrosive, they are cladded with a thin layer of aluminum for added protection.

Working With Aluminum Tube

For the most part, the two fabrications tasks needed for aluminum tubing is bending and connecting. 

When it comes to bending tubes, there are three main factors to be considered:

1. Formability

Some aluminum alloys, the 3xxx, 5xxx, and 6xxx series for example, have a higher degree of formability than others, making them good materials for bending. Often, higher formability alloys also have lower  strength.

2. Thickness and Bend Radius

Aluminum, like other metals, “work-hardens” during the bending process, which means that it gets stronger and harder as it’s formed. However, If the radius is too small compared with the thickness of the tube, the material will be overworked and more likely to fail.

3. Percentage of Elongation

The percentage of elongation is a way to describe the difference between the metal’s yield strength and its ultimate tensile strength. Yield strength is the point where an aluminum alloy can be bent and no longer return to its original shape. Tensile strength, on the other hand, it the maximum stress that can be applied to the aluminum before it breaks. The greater the difference between these strengths, the more formable the alloy.

Connecting tubes usually means one tube to another or one end to a receptacle of some kind. Most commercially produced tubing can be had with connectors designed for specific types, shapes and dimensions of tubes. 

Another approach is brazing or welding tubes. According to an article at Machinedesign.com, 

“Welding joins metals by melting and fusing them, usually adding a filler material. Fusion requires concentrated heat directly at the joint, and temperatures must exceed the melting point of the metals and filler. Welded joints are usually as strong or stronger than the base materials.

Brazing differs from welding in that the temperature is considerably lower and does not melt the base metals. Rather, the heat source melts a filler metal and draws it into the joint by capillary action. It creates a metallurgical bond between the filler metal and part surfaces.

Like welding, joint strength often exceeds that of the individual parts. For instance, the tensile strength of stainless steel joints can exceed 130,000 psi. But because brazing temperatures are lower, generally 1,150 to 1,600°F, most physical properties remain unaffected. Distortion and warping are minimal, and it minimizes stresses in the joint area.”

Regardless of whether you need 100 feet of an aluminum extrusion product, or just a few feet of stainless-steel tubing, AAA Air Support promises to always ship out your part orders quickly and efficiently. Our goal always is to provide your company with the means to complete that project or get that airplane back in the air in AOG situations.