Structural Integrity

Reference books on the subject for aluminum are relatively recent. The first one¹ that was published in Canada was released back in 2003, while the revision of the CAN/CSA S157-05 standard is more recent. The training of engineers in universities cannot be done without these tools. These resources are, however, critical to engineers’ training. That’s
why the aluminum industry has to proactively approach institutions to educate them about the importance of including the sustainable metal in their curriculum. Initiatives to encourage on-the-job training, like scholarships and recycling courses, are relatively recent.

For a long time, universities have offered undergraduate programs that essentially focus on traditional materials like steel, concrete and wood. The tide is slowly starting to turn, but aluminum does not yet enjoy its rightful place in university programs. That said, the rising cost of steel means that more and more engineers and architects are turning to aluminum. And that’s great news, because as demand increases, so will the need for training.

Civil engineering courses teach future engineers to calculate the forces to which the elements of a loaded structure are subjected. The materials used in structures such as steel, concrete, wood and aluminum each have their own mechanical characteristics that must be taken into account in the detailed calculations.¹ Since they’ve been used for so long, the characteristics of old traditional materials such as steel, concrete and wood are integrated into structural design software, but not aluminum. For reasons related to manufacturing difficulty, traditional materials are made available in standard profiles, which make it easier for engineers to learn how to use them, ensure compliance with standards and ultimately choose those materials. But aluminum’s extrudability allows for complex shapes and contours, providing a clear advantage for structural design.

Additional training is offered to engineers working in the aluminum industry to address the lack of training with aluminum alloys. Some are ad hoc,² while others are offered as part of specialized training.^3,4 Since these short programs are offered on a one-off basis, it’s best to check the schedule directly with the institutions offering the training.

When we talk about aluminum, we are referring to aluminum alloys. There are many welding techniques, and some of them are well suited for welding aluminum.^1, 2 The choice of welding techniques will depend on the shape of the part, the quantity and the alloys to be welded.

Fusion welding of metal at a joint, with or without the addition of metal, does not give satisfactory results with some alloys. The existing knowledge base includes all the practices and advice for welding an alloy or alloys together, as well as the ideal alloy for the filler metal (generally required) using a particular welding technique (e.g., TIG, MIG, etc.). The aluminum alloys used for manufacturing are delivered with enhanced mechanical properties through heat treatment and/or mechanical treatment, which hardens them. The temperature reached in the joint largely eliminates this hardening. It’s the role of engineers to take this into account in the design of a part, which often leads to a more or less oversized part.² 

Friction stir welding, a fusion-free welding technique almost exclusively used for aluminum, makes it possible to weld all alloys without almost any loss of mechanical properties, including for problematic foundry alloys.³ When geometry and quantities are adapted to the process, this technology can become an essential asset for aluminum and product quality.

A structure is the framework that supports all loads such as traction, compression and torsion. If the loads are static and the strength limit of the material is respected by the design, in principle the service life is infinite if corrosion is ignored. However, when the mechanical stresses appear as cyclic loads, metals will suffer damage such as material fatigue (i.e., appearance of micro-cracks), leading to failure after a number of cycles depending on the weight of the load. ^1, 2

When it’s possible to see this type of stress, it’s possible to predict the service life before failure occurs. This is thanks to the large number of mechanical tests performed on each metal. Since the loads on structural elements depend on the design, engineers design the structures and dimensions of the structural elements and their connections (i.e., welded, glued, bolted) to ensure a sufficient and safe service life for the selected metal alloy. Steel has the uniqueness of having a stress threshold that gives an infinite service life. A design based on this threshold is not optimal or required for all types of structures.

The level of safety is partly based on a lack of knowledge of in-service stresses, so designers who want to lighten the components of their structure (e.g., frame members and vehicle chassis) compile data to measure these in-service stresses. For optimal product use, it’s often necessary to decide on the service life requirements during the design phase.

It all depends on the contact conditions. To be sure, contact between steel and aluminum can accelerate the corrosion of aluminum, so this issue should be considered. Without the presence of water to act as a conductive liquid, galvanic corrosion cannot occur.^{1, 2} Metal contact between aluminum and steel is also required to form a short-circuit and create a corrosion current, as in the case of a battery. 

In the case of rain that can dry, when the wetting time remains short overall, galvanic corrosion may not be a concern. But in any environment exposed to water, short-circuiting is prevented for bolted connections by placing insulation (preferably waterproof) between metal surfaces (steel-bolt-aluminum) or by using a coating on the surfaces to isolate them from each other or from water. In some environments, stainless steel bolts can be used to assemble aluminum. A phenomenon called passivation considerably slows down galvanic corrosion of aluminum, but the time it takes for this type of assembly will need to be taken into account. 

Aluminum is more “noble” than zinc, so it’s protected by the zinc coating on galvanized steel. But since zinc is similar to aluminum, it will corrode slowly, making it important to plan ahead for when this protective zinc coating disappears.

The density of aluminum is three times lower than that of steel, which gives aluminum a definite advantage for transportation. 

Electrical and thermal conductivity depends on the purity of the metal, but generally speaking it is three times higher for aluminum. Combined lightness and conductivity make aluminum indispensable for power transmission lines. The melting temperature of aluminum alloys is about two times lower than that of steel, which means aluminum can be cast in steel molds, a method that considerably reduces manufacturing costs.

Aluminum is also very malleable at a temperature near its melting point, making it very easy to extrude. This “extrudability” makes it possible to create highly complex aluminum profiles that would be impossible to produce using steel. Aluminum offers enormous potential for designers and product design engineers alike.

Aluminum is obtained through the electrolysis of alumina. But where does alumina come from, and how does the liquid aluminum produced in this way become the lightweight parts used by MAADI Group to build such strong structures?

This website gives an overview of the stages leading from bauxite—the main ore used in aluminum production—to finished products. Other diagrams illustrate these different steps:

• Alumina (Al₂O₃) is chemically extracted from bauxite, which generally contains 40 to 60% of the compound.
• Alumina is then melted at around 960°C and then, through electrolysis, the alumina splits into oxygen and aluminum (Al). 

Various avenues allow manufacturers of finished products to take advantage of the extraordinary potential of aluminum, such as:

• Development and casting of specific alloys into ingots, billets, etc.
• Moldings that meet the specific needs of transformers, such as the different nodes designed and used by MAADI Group to manufacture MakeABridge^® bridges.
• Ingot rolling and billet extrusion, like the extrusions designed and used by MAADI Group to build its structures.

Quebec producers ensure that each of these steps is carried out with respect for the environment and human health. These producers ensure that the aluminum produced in Quebec is one of the cleanest—if not the cleanest—in the world. For this reason MAADI Group is proud to use Quebec-made aluminum in all of its products, including gangways, pedestrian bridges, marina decks and more.