The Strength of Aluminum Welding

Workability

• Aluminum is very difficult to weld. This has been one of the main reasons for this metal alloy's bad reputation for its welding strength. Aluminum melts far faster than steel. It is softer than steel and requires specialized equipment for working. Cheaper grades of aluminum contain magnesium, which makes life even more difficult for welders. One important problem is that aluminum expands rapidly as it is heated, introducing more air into the weld joint. Therefore, under most circumstances, the weld will be weaker and generally of inferior craftsmanship for this reason. Since aluminum is a soft metal, it is less resistant to heat.

Weakness

• The Lincoln Electric Co., headquartered in Cleveland, specializes in all forms of welding. This firm claims without caveat that aluminum is “always” weaker than its parent metals. “Parent” here means the metal by itself. In the case of steel, a steel weld can be stronger than steel by itself. For aluminum, however, the opposite is true. It is always weaker. The company claims that the welded joints in an aluminum structure are as much as 30 percent to 40 percent weaker than the aluminum by itself.

Steel

• Aluminum by itself is stronger than steel usually by a factor of 3. This means that the “impact strength” of aluminum is three times better than steel. In simple terms, this is because when aluminum is put under stress, it dissipates the energy of the stressor. Steel takes a hit directly at the point of impact. Aluminum has the tendency to take that energy and spread it around, lessening its immediate impact. This means that even the weaker joint of welded aluminum might be as strong as solid steel, since aluminum itself can be as much as 300 percent as strong as steel. If aluminum weld joints are 40 percent weaker than aluminum by itself, this suggests that even a welded joint will still be stronger than steel.

5383 Grade

• On the other hand, the Alaskan Copper & Brass Co. and Alaskan Copper Works argues that its own 5383 grade of aluminum welds stronger than that grade of metal by itself. The company claims that, properly treated and worked by competent welders, the 5383 grade will develop welded joints about 15 percent stronger than the aluminum by itself. This grade is more expensive than the typical aluminum metal. It needs to be ordered specifically for welding because it is specially treated at the factory.