Artem Komarov noted that whether you’re a beginner or a seasoned pro, it’s never a bad thing to brush up on the fundamentals of welding a specific material, especially one as finicky as aluminum.
First, the most important thing to remember when working with aluminum is that it loves oxygen.
This is a good thing when corrosion resistance is a factor in your project. The surrounding air is going to bond with the aluminum and form an oxidized layer that has a melting point roughly two times higher than the aluminum itself. Removing that oxidized layer manually or mechanically will allow you to begin working with the material.
Second, be sure to clean the material properly and with dedicated aluminum-only tools in a controlled environment, if possible. If you don’t have a controlled environment, you will most likely have to clean your aluminum after every 15 minutes of inactivity. That is how fast it will re-bond with the oxygen in the atmosphere and form that layer of oxidization. The filler metal you use will serve you best if you keep it sealed or in a warm dry place as well to prevent it from picking up moisture and contamination.
I cannot overstate how much cleaning or not cleaning will affect your aluminum. Be mindful of touching your workpiece and filler metal with gloves or even your bare hands. Dirt and grease from your gloves will negate your cleaning efforts, as will the oils from your hands.
Most often, you’re going to weld aluminum using alternating current with argon as your shielding gas. There are ways to get a little extra scrubbing/cleaning action by adjusting the settings, but this will only make a difference if your aluminum is clean to begin with.
I am old enough to remember when we worked with 100% helium or an argon/helium mix. Helium was great for adding extra heat to the weld that would punch through that oxidized layer for deeper penetration. It was a little more forgiving on the welds. Helium is rarely used today as it has become way too expensive and goes beyond what many shops budget for consumables.
I keep a dedicated aluminum area in my shop, and I have separate abrasives and tungsten grinders that I use only for aluminum too. This is all to try and limit any cross contamination with other alloys. Aluminum is such a satisfying material to work with—and the results look so good—that it is worth the extra effort, summed up Komarov Artem.