After welding, aluminum will become weaker than the base material. If you're used to working with metals such as steel, you might assume that a finished aluminum weld will be just as strong. Unfortunately, non-heat treatable aluminum is usually hardened via a process known as cold working.
Welding aluminum generally will weaken it, and for a few different reasons. The main reason is that heat will affect the temper of the aluminum, which can result in a loss in yield strength of roughly half in many cases if measures aren't taken to correct it.
When welding aluminum, the material transition from the filler material to the base material mainly produces what is known as aluminum oxide, which can be found in the form of particles in the welding fumes. These particles can range in size from 10 to 400 nanometers, depending on the welding process used.
These heat-treatable metals have an ultimate tensile strength of 18,000 PSI to 58,000 PSI. They contain a small amount of magnesium and silicon—around 1.0 percent. They are used widely throughout the welding fabrication industry, predominantly in the form of extrusions, and incorporated in many structural components.
You lose close to 40 percent of the strength of the 6061-T6 when you weld it. Therefore, if you will weld 6061-T6 in your project, you need to base the design on this lower strength.
6061 is highly weldable, for example using tungsten inert gas welding (TIG) or metal inert gas welding (MIG). Typically, after welding, the properties near the weld are those of 6061-0, a loss of strength of around 80%. The material can be re-heat-treated to restore -T4 or -T6 temper for the whole piece.
The aluminium alloys (5xxx) series can generally be regarded as a two re-weld operation but the (6xxx) series is far more sensitive to heat input and even a single re-weld operation is undesirable.
All of these alloys are heat treated by precipitation hardening. This involves two steps—solution heat treating and aging. Solution heat treatment is done by raising the alloy temperature to about 980 degrees F and holding it there for about an hour.
The thickness of aluminum in industrial welding applications typically ranges from 1/8 inch to 16 gauge, but you may be welding up to 3/8 or 1/2 inch in some cases. Gas and filler metal selection, as well as proper technique, may differ depending on the material thickness and the goals of the application.
One of the most popular welding processes for aluminum is gas tungsten arc welding (GTAW), otherwise known as tungsten inert gas (TIG) welding. GTAW is a great process for aluminum because it does not require mechanical wire feeding, which can create feedability issues.
2000 Alloys:
This is a family of high-strength aerospace alloys. They are extremely sensitive to hot cracking and are the least weldable aluminum alloys. Specifically, 2024 is the least weldable. But there are a couple exceptions, 2219 and 2519, which can be readily welded with 2319 or 4043 filler metal.
Corroded aluminum weakens the metal over time. In a mild climate aluminum corrodes very slowly. Atmospheric factors like rain, humidity, acidity, and other chemical stressors make aluminum corrosion more likely. Cleaning and drying can help aluminum that is in regular contact with stressful climates.
Welding can weaken steel, particularly in the heat-affected zone (or HAZ) when welding at high temperatures. Weakening with welding is most common with cold-rolled steel.
Stress cracking can occur when an aluminum weld cools and excessive shrinkage stresses are present during solidification. This could be due to a concave bead profile, a too slow travel speed, a highly restrained joint, or depression in the end of the weld (crater crack).
Aluminum has high thermal conductivity; this being a property that may affect distortion and can substantially affect weldability.
A small amount of gallium will destroy anything made out of aluminum, including aluminum cans. It also attacks steel, making it very brittle.
Welding aluminum is very different when compared to welding steel, both in technique and in results. Welding aluminum generally will weaken it, and for a few different reasons.
Most aluminium alloys can be joined by welding together; however, certain aircraft-grade aluminium and other special alloys are unweldable using conventional methods. Aluminium is commonly welded with gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW).
Article Revised July 28th, 2022. It's often said that aluminum is a more difficult metal to weld than steel. While it's true that most welders start out by learning to weld steel before moving on to aluminum, it's not entirely accurate to say that one is more difficult than the other.
Zinc (Zn) 7xxx – The addition of zinc to aluminum (in conjunction with some other elements, primarily magnesium and/or copper) produces heat-treatable aluminum alloys of the highest strength. The zinc substantially increases strength and permits precipitation hardening.
Benefits of Precipitation Hardening
Precipitation hardening creates a harder, stronger metal. Aluminum is a fairly soft metal, so this process can significantly increase its yield strength, increase its tensile strength, and increase its wear resistance.
Depending on the filler rod alloy the yield strength is reduced from 40 ksi to 18 ksi(4043 alloy rod) or 19 ksi (5356 alloy rod).
Is Welding Aluminium Difficult? Aluminium alloys pose a range of difficulties when welding, including: High thermal conductivity. This results in excessive dissipation of heat, which can make welding difficult and/or result in unwanted distortion of the parts, owing to a larger heat input being required.
Types of metals: MIG welding works with most types of metals. You can use aluminum, stainless steel and mild steel. TIG welding is also compatible with these metals but works better with thinner gauge materials. Speed: TIG is a slower method but provides a higher level of detail.
TIG Weld Seam
Aluminium is much more difficult because the material is surrounded by an oxide layer. This melts at a much higher temperature than the base metal. Therefore, the oxide layer needs to be removed or disturbed in order to produce an integral weld.