black smoke on alu weld

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Hello. I am new here. Can anybody help? I have a signmaking shop, we produce channel letters from alu and use a FRONIUS MIG transpulse 2000 machine which has several programmes for steel, stainless and alu. The welds on alu look great but the bigest problem for us is to get rid of the black oxidation (soot) that forms on the welds. We tried lots of procedures, detergents, thinners, gasoline, etc. Most of the soot goes off but a small portion stays. Anobody has a better idea how to finish the welds?
Reply:Maybe the problem isn't with the finishing..It may be with the "starting"...Try cleaning all the whatever off so you have good clean metal..You mention its with the aluminum..Clean the weld area with acetone and a stainless steel brush..Shiney is better..The black soot comes from comtamination..No contamination = pretty welds!...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:In addition to cleaning the base materials, don't forget the shielding gas.What gas are you using?  What flow rate?  Do you push to shield ahead of the MIG weld?  Do you preflow to make sure the starts are shielded?  Any leaks in your gas delivery system?  All things to make sure of also.Favorite right now is a Miller Syncro 200.Tons of tools and I blame at least one of them when things don't go right.
Reply:sounds to me the previous poster hit it, you aren't using c25 on the alum. are you? you need to use straight Argon
Reply:A small amount of black soot is common and should be cleaned off immediately with a stainless brush.  You can get small toothbrush size stainless brushes that you can stick in you vest pocket.  After all welding and handling is competed you need to spray the part with an acid aluminum wash then rinse with water.  The stuff is phosphoric acid based.  You dilute it with water and spray it on with a trigger sprayer if it is a smaller piece or a garden sprayer if you are doing larger pieces.  Careful application is important to prevent streaking.  The acid wash will take trace amounts of soot off only.
Reply:Thanks Zap for your info, but in 90% of jobs I use only new aluminium sheets and extrusions. Maybe the culprit is the wire I use? Its AlMg5 alloy. The preflow of gas (Argon 4.6) is O.K. It must be the wire because the soot is allways present. I do various jobs - frames from new extrusions, letters from sheet alu, also repair jobs of automotive pieces (motor blocks, cast parts etc.) the black smoked surface is on all welds.
Reply:Originally Posted by RadanThanks Zap for your info, but in 90% of jobs I use only new aluminium sheets and extrusions. Maybe the culprit is the wire I use? Its AlMg5 alloy. The preflow of gas (Argon 4.6) is O.K. It must be the wire because the soot is allways present. I do various jobs - frames from new extrusions, letters from sheet alu, also repair jobs of automotive pieces (motor blocks, cast parts etc.) the black smoked surface is on all welds.
Reply:The black soot is more common with the 5000 series alloys, than the 4000 series alloys, this is due to the 5000 series being a magnesium based alloy, and the 4000 is a silicon based. What causes the soot is the aluminum and magnesium alloys combine to form these black oxides. these oxides have a lower boiling point then the temperature of the arc, they evaporate and condense on the weld and haz area. Excess soot can be an indicator of porosity. Here are a few things to check/try:Excess soot can be caused by:1.) too long of an arc length, either by operator stckout, or excess voltage.2.) not enough weld energy, increase wire feed speed, or drop down a size in wire to increase current density.3.) Incorrect direction of travel, you'll always want to use a push for aluminum4.) Incorrect Gun angle, next time you are playing around with some scrap, vary your gun angle, you can actually move the soot from one side of the weld to the other just by changing gun angle. 5.) Travel speed too fast, which doesn't allow sufficient breakup and removal of the outer oxide layer. 6.) Insufficient gas flow coverage, do you have a way to check flow at the nozzle? I never trust what the flowmeter or regulator reads, the only way to know for sure is to check the flow at the torch, I had a post on this site a few months ago about a customer that was having porosity issues on his push pull aluminum mig set up, he had his flowmeter set at about 35 cfh, but was only getting around 10 cfh at the nozzle, I had to turn his flowmeter to 55 just to get 25 at the nozzle, once we did that his porosity issues went away, this could have been caused by a bad liner, bad flowmeter, etc. What model of Fronius do you have? I've never seen the 2000 model, I've sold a few of the Transpulse 2700 units, (all for aluminum) and those are one sweet machine!! Good Luck, and let us know how you come out.
Reply:In the end you are gong to have to clean the material properly to get the last of the soot off.  It will attract moisture and accelerate corrosion.  On this project involving over ten bridges over fifty feet long we had to acid wash and pressure wash.  If you are doing signage it will be important. Attached Images
Reply:Radan, since you are using the alum. as signage, it may be a situation like boat work, where you can't scratch up the pieces with a ss brush. I have migged a lot of aluminum in the past, the black soot is just always present. I do scrub the material after welding with a stiffer plastic bristle brush, then lightly polished it.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:Did anyone mention that the wire (rod) should be cleaned with acetone ,also, BEFORE you start welding. The welding area should be scratched RAW(clean) with the stainless brush, before cleaning it with the acetone. I tell people that clean or sanitary is not good enough, it has to be sterile !Except for Titanium, aluminum is probably the most difficult to weld. Remember , the surface oxides don't melt untill 3,600 degrees F. the raw aluminum melts at about 900 degrees (in that region)[SIZE="5"Yardbird"
Reply:Did anyone mention that the wire (rod) should be cleaned with acetone
Reply:Look at this welding alum link, it makes some good points...Bobhttp://www.thefabricator.com/Aluminu...cle.cfm?ID=554Bob WrightSalem, Ohio  Birthplace of the Silver & Deming Drillhttp://groups.yahoo.com/group/southbend10k/http://groups.yahoo.com/group/sawking/1999 Miller MM185 w/ Miller 185 Spoolmate spoolgun
Reply:Originally Posted by tanky321Even if the aluminum is new you still need to clean it. AL forms an oxidizing layer on itself.
Reply:Okay, I think I am a lot smarter now. I noticed that the soot is easier to clean exactly after the welding. When the metal is cold, its harder. I will try the acid, but I am afraid that no shop for welders has it. Surely the supplier of chemicals will have it. To Lotechman: Phosforic acid you saidTo SS: Yes I have the 2700 model, an error came in. I have traded it for signs that we produced for Fronius branches in our country. Its a dream machine. Just change the gas, wire and pulleys and we can weld steel, ss and alu with one machine. I will try your remarks thanks.To Rojodiablo: You are right. Most of our welds are grinded and spraypainted but some must be visible and nice, just like welds on a motorcycle or bicycle frame. Thats the point why I asked here. At this moment we are fabricating a aluminium truss girder with visible welds. I cant scrub it with a steel brush because it scratches the surface around. We work in gloves when manipulating with the piece. I have tried a rice brush, it works ok. Just needed the info about the acid. Anybody tried sodium hydroxide ? I have heard its very agressive to alu. We use it to clean blocked sewers in our country. Small white tablets mixed with hot water.to: AAmetalmaster: Thanks for the linkAnyway I am wondering about a TIG machine to produce those master welds seen on japanese motorcycles. How long it takes to master them? People say the work is a lot slower than MIG. I think I am really good with clasic electrode and MIG having 20 years of practice, but need a little push to start TIGing (and also some money) Hey you guys, have to go to work now, no time for sitting on the net.
Reply:I've seen a LOT of aluminum welds on Jap bikes, and most of what I see isn't impressive to say the least.  To achieve that type of bead appearance isn't too difficult.  They use larger diameter filler (1/8" or so) to give that appearance and to make the work go more quickly.  Harley Davidson does the same thing with their aluminum, as do many other manufacturers, its just more visible on the crotch rockets.
Reply:Actually most the aluminum welds on the bike frames are pulse mig, computer controlled.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:RE phosphoric acid wash :  Try this site and read the MSDS.  You chould be able to find a similar product in your area.http://www.orisonmarketing.com/corro...luminator.htmlBe mindful that you can create streaking if you apply this in patches.  On large stuff we had one person spraying on the wash solution then another following with a high pressure hose.  Depending on the concentration a minute soaking time is usually enough.
Reply:I have a similar problem, except it is welding on older aluminum livestock trailers.  I discovered that the acids in the manure as well as the grinding action of the hooves of cows have a tendency to really push contaminates into the aluminum making it impossible to weld.  I have used acetone all the way up to muriatic acid and even grinding to clean the metal to mig it with a spoolgun, and it still blows black but for all the problems, brushing with a good wire brush right after welding helps to make it look like I knew what I was doing
Reply:If the welds are smooth, use a Scotchbrite pad to remve the black.
Reply:Just tried the phosphoric acid on my girder job. Its fantastic, after 3 minutes the welds are shiny and nice. Thanks a lot lotechman.
Reply:anyone tried bead blasting?  i've had good results, though its only practical if you can fit the part in the cabinet.
Reply:I just bought some Eagle One Aluminum wheel etching stuff in a spray bottle from Autozone.  It works wonders.  Spray on and rinse off after 30 seconds.  I used it on my aluminum flatbed and boxes.  Only problem, they had ONE bottle in stock.  Gotta get more.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Originally Posted by RadanJust tried the phosphoric acid on my girder job. Its fantastic, after 3 minutes the welds are shiny and nice. Thanks a lot lotechman.
Reply:I remember when I was in high school, I worked after school for a friend doing ALOT of Al MIG with a Cobramatic. After a batch of parts were welded, we used to soak them in a diluted acid wash. If my memory serves me right I believe that ZEP made the solution that we diluted. Just dropped them in, swirled them around for a few minutes and hosed them off. They'd come out clean as a whislte.Originally Posted by ss42768The black soot is more common with the 5000 series alloys, than the 4000 series alloys, this is due to the 5000 series being a magnesium based alloy, and the 4000 is a silicon based. What causes the soot is the aluminum and magnesium alloys combine to form these black oxides. these oxides have a lower boiling point then the temperature of the arc, they evaporate and condense on the weld and haz area..........