Full size drawing
We are finishing a home renovation and I had to put the metal shaping and restoration work aside to make some deck railings for my wife. After all; happy wife, happy life. So if I want to get some shop time I'll need to work on Linda's house project first. I've never worked with aluminum before and have been looking for an opportunity to expand my skill base. So this worked out well for me.
The rails are a copy of some Chinese Chippendale style rails I made out of treated wood for the original deck on our house 20 years ago that was replace with an addition to the house. The goal was to make things as maintenance free as possible, so I decided to use 6061 T6 2" X 2" aluminum with 2" X 3" top rails and 3" X 3" posts (all 0.125" wall thickness) and powder coat them.
I have never welded aluminum before and certainly not TIG welded aluminum. What I'm offering here is not an expert session in how to TIG weld aluminum, rather the things I learned while doing this for those others who are attempting to learn to TIG aluminum on their own. I'll also show the process I used to build the rails as we go along.
When starting to TIG aluminum you will find that it requires much more amperage than you normally use for steel. I set my welder at 180 amps AC to weld this 0.125" stock. This is because aluminum transfers heat rapidly as we discussed earlier. That's also why a lot of cookware is either aluminum or has an aluminum plate sandwiched between other materials. Also, aluminum doesn't change color as it is heated. The TIG welder I used is a square wave AC type which provides a cleaning and welding alternating arc that switches between electrode positive and electrode negative. The white area you see around the bead is the result of the cleaning arc. Contamination is much more of a problem with aluminum than steel and care should be taken to make sure all contaminants are removed. When the molten puddle forms it will appear as a shinny puddle looking much like a dot of mercury. One of the hardest things for me to learn was to be patient and wait for the puddle to form. As we discussed earlier, it takes a while to heat up aluminum and for the puddle to form...I was afraid that I would blow a through the stock before the puddle formed. The other thing I had to learn is how to use the filler rod with aluminum. I usually try to hold the filler rod in the path of the shielding gas when welding steel. The aluminum filler rod will melt if held close to the torch and a blob of molten aluminum will form at the end of the rod. The rod has to be dipped into the puddle as the weld progresses, so I developed a technique of moving the torch forward and pushing the puddle as you would while fusion welding then backing off slightly which allowed me to dip the rod in the molten puddle...then push the puddle forward and repeat. After a while a rhythm forms and it gives the experts the stack of dimes look on the finished weld. I'm not that good yet. While doing this, it appears that it would be easy to just fusion weld...don't do it. The material I found indicates that fusion welding aluminum results in cracked welds...filler rod has alloys that promote bonding and prevents cracking and should always be added to aluminum welds. There are 2 types of aluminum filler normally used with 6xxx aluminum: 4043 and 5356. The 4043 flows very well and is more malleable which helps prevent cracking. The 5056 is harder and results in a harder, stronger weld but can crack if not properly used. I had more trouble with fillet welds than the butt welds and was told by a friend that the 5356 makes fillet welding a little easier because it melts at a higher temperature. I tried it and it worked for me. Once you get the knack of building the puddle and moving it along while dipping the filler rod in the puddle, you will find that you are controlling the amperage with the foot peddle without thinking about it. Watching the base metal and the puddle requires adjusting the amperage to keep the base melting into the puddle and the puddle moving. Also, as the bead moves along, the aluminum heats up and requires a little less amperage or it can blow through. One of the hardest habits for me to form was to only dip the filler rod in the puddle and not heat it with the torch.
Got the rails back from powder coating and installed the short rail on the deck myself. I needed some help to get the 12 foot long rail up on the deck to install it. Although they are aluminum, when you get enough aluminum into a project it can get heavy.
Assembly table construction
The rails are now at the powder coater...I will publish pictures of them when they finish coating them and after they are installed.
Second rail section
I found TIG welding aluminum is much different from welding steel. I practiced on some scrap pieces before I started welding on the rails. I also went back to the notes I took during the 3 sessions I had with Fay Butler (faybutler.com) and referenced the AWS texts. The process is based on the specific properties of aluminum that make welding it very different from welding steel. Aluminum very quickly forms aluminum oxide on its surface and aluminum oxide melts at a higher temperature than the base material. This requires that the oxide be removed in the area to be welded by scraping , filing or brushing with a stainless steel brush. Don't try to use a sanding disk...it will just embed the oxides in the base material. Also, the files and brushes used on aluminum must only be used on aluminum or they will contaminate the welds. You also have to clean the material to be welded with a solvent such as acetone to remove all hydrocarbons which will also contaminate the welds. Then there is the filler rod. It also is coated with aluminum oxide and probably with hydrocarbons from the manufacturing process. It has to be cleaned with a solvent and the oxide removed. Fay Butler recommends you clip the end of the rod before beginning welding for a fresh end with no oxide. I normally TIG weld steel with 2% thoriated tungsten electrodes but aluminum shouldn't be TIG welded with thoriated tungsten. I used 2% lanthanated tungsten with good result. Aluminum is TIG welded in AC mode and the tungsten will form a ball on the end that will be used rather than the point used with DC welding steel.
Finish welding each piece
Pieces tacked together
12 foot table
The first thing I did was make a full size drawing of one section of the rails. Then I laid the drawing out and cut 0.250" plywood patterns which I used to cut the 2" X 2" aluminum center rails. I then put together a table the size of the longest rail section (twelve feet) and the height between the top and bottom rails, then assembled the aluminum sections for welding. I changed the process on the second rail section I built. I found out the the aluminum expands rapidly while welding which broke several sections of the tack welds I placed while assembling the whole railing before final welding...a process I normally use with steel. Aluminum transfers heat throughout the piece being welded quickly and heats up the whole piece because of it's heat transfer properties rather than just the spot being welded as in steel. This "grows" the piece being welded much more than normally experienced when welding steel. So, on the next section that I built, I cut and final welded in each piece as I went along rather than assembling the whole rail section, tacking in each piece, and then final welding. That worked much better and resulted in a much better outcome.
The finished rails just before loading them up to go to powder coating.
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