Posted 17 August 2012 - 07:57 AM
Posted 17 August 2012 - 08:24 AM
Porosity in casting is always a concern, with aluminum.....it LOVES hydrogen when it's molten.
Edited by ornametalsmith, 17 August 2012 - 08:29 AM.
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Posted 17 August 2012 - 09:18 AM
Posted 17 August 2012 - 11:17 AM
Posted 21 August 2012 - 03:09 AM
We use borax in the bronze, brass and white brass melts to keep oxidation from occurring and I have something for the aluminum as well (can't remember what it is called though). We do have an electric melt induction furnace but it is less predictable than the glory hole so I kinda scraped it a few years ago. Plus we do production runs of up to 500 or 600 pieces with limited time so 1/2 hour melts for each flask just doesn't cut it.
Are you using any sort of hydrogen/oxygen scavenging substance in your melt process? I have very little experience with aluminum, but in copper alloy castings it is often necessary to add a scavenger to eliminate porosity from absorbed oxygen. An induction furnace running an inert atmosphere purge is the typical production solution, but not everyone has that capability. I'm sure there must be a chemical you can add to the melt to address this issue, though. Just have to locate the source.
Posted 21 August 2012 - 03:16 AM
Posted 21 August 2012 - 10:10 AM
Aluminum welding is very similar to welding bronze (copper alloys) in that you need to stomp the pedal at the start to overcome the high thermal conductivity of the metal and then back off to your welding power. One big difference, other than the need to use AC instead of DC for aluminum is that aluminum is going to try to oxidize much worse during welding than bronze will. Also the range between liquidus and fluidus is narrower on the aluminum so you have to watch out for burn-through. The modern inverter TIGs that have pulse control really help in this regard as you can fine tune the "on" times to get really nice stable welds. But even with an old transformer-type like my Syncrowave 200 you can get good welds on aluminum with a bit of practice.
One caveat - welding cast aluminum is three times trickier than welding billet or plate. Any difference in density on a casting, or any included detritus like flux or dross, will become immediately apparent when welding it - that's almost always where you'll get the burn-through and/or heavy oxidization. So the quality of your casting will influence the quality of the welds on it.
Edited by Rich Waugh, 21 August 2012 - 10:11 AM.
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Posted 21 August 2012 - 01:06 PM
What Rich said. Also be sure to wire brush the oxide off the aluminum before you try welding it.
Use only stainless steel brushes that are only used for aluminum. and no cross contamination from ferrous metals.
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Posted 22 August 2012 - 12:37 AM
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