Pre-heat alum?

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Hey y'all, maybe one of you alum experts can help me out w/this.Couple of months ago I had a field call to weld a tail gate clamp on a alum body rock truck. You know, one of the rounded side, forty foot long trailers. Thursday I got a call to go back and put it back on 'cuz it had "popped" off.   After looking at it(and cussin' a bit) I cleaned it off and re-welded it.First off, let me say I'm no alum weldor. My exp. there is very limited. We have a Miller trailblazer with an spool gun and all we did was fiddle with it in the shop 'till I got a decent bead.The broken part had some cold lap that I could see but for the most part the weld held and the bracket itself broke right beside the weld.I was using 4043  .035 wire. The truck channel is a formed 1/4", the brkt is 5/8 thick.All the parts were clean and I do know what a good pass looks like.Should I have pre-heated it? I did the second time but only because I thought I needed to do something different.(after all, it did break)'I'd like to post pics but I haven't figured out how yet. thanks for the help, I really appreciate it. I hate come backers.Last edited by TEK; 09-06-2005 at 12:57 AM.
Reply:I have never had to anneal (pre heat) aluminum before welding. I can tell you that the 4043 is a brittle wire and I would not suggest it for this type of welding 5356 would be a lot less subject to cracking. This may be part of the problem but you had said the weld did not fail just the part. What part of the end dump trailer was it. "Tailgate clamp" was it the safety latch that holds the tailgate shut? ( fork shaped block with a long all thread bolt and wing nut? just trying to visualize what part. Do you know make the trailer was? Pics would help. there is a chance that the driver tried to dump with the latch shut causing it to fail. That would be no fault of your own.Last edited by Robby T.; 09-06-2005 at 01:30 AM.
Reply:Robby T, thanks for the quick reply! Yes, it is the safety latch. Don't know type of trailer.We do have 5356 wire so if it happens again I will be sure to use it.(Why didn't bossman tell me?) Any particulars with this wire I need to know? Was it bad to pre-heat? Maybe post-heat? Alum is a whole different ball game!!! Thanks again!!!!Tim
Reply:i dont think it would be bad to pre heat. after all the welding will heat the part anyway. I have welded this part many many times Tek. New ones on new trailers, replacements on old trailers and cut off or broke ones on old trailers. I have never seen one just "pop off'. When I weld the older ones I grind down the corners for a bevel then weld uphill. Did the weld look cold to you? I would have to say it was the brittle wire or the driver dumped with it shut. As far as the 5356 wire it is just a softer alloy and more suited for applactions where high stress or vibrations are involved. these guys will keep you busy dump trailers are very prone to cracking and must be welded to keep the Department of transportation from red tagging them.
Reply:Robby, I have welded on this outfits trucks more than a couple of times but it has always been on thinner stuff. The brckt was 5/8" so I thought maybe bad procedure was prob. There was one spot about an inch long that looked like it was a little cold but mostly the weld was ok.I did the verts uphill and they looked ok goin' in. And yes, those truckers will keep you busy!!Thanks again,bud, and have a good day tomorrow.
Reply:More than glad to help Tek. I dont allways know how much the posts do help but I will try my best. When it comes to these dumps I most often know somebody that can. I had a blast today I am in the process of opening our new Ft. Worth Repair facility. Been rigging out new welding machines and all the other shop stuff and building tables and benches. Getting ready for buisness. It's been great. I put together a hell of a package I think. a miller CP 302 with R22 feeder and a Miller Delta Weld 452 Rigged out with profax spool gun with 50' leads and 50' cables for gouging with the same machine both complete with running gear and bottle racks. Also a thermal dynamics pakmaster 100 plasma torch. I'll try to get some pics on later.Last edited by Robby T.; 09-07-2005 at 01:14 AM.
Reply:Sounds like it'll be a real nice shop. Lotta good gear you got. good luck with it.Also, your post was helpful, got me to thinking on a couple of things(DANGER,DANGER)
Reply:hear is the problem with thick aluminum you need a bottle of helium mix. which is 75% helium and 25% argon. the helium adds some serious heat to the puddle area and allows to penetrate more. if it is cold outside preheat the aluminum cause helium has a tendency to crack at the crater.when welding aluminum 3/8 or thicker material you need helium. with heliarc or mig aluminum gun the 5356 wire is perfect.have anymore questions feel free to ask..............
Reply:Liquid Weld420, thanks for the imput. The more knowledge I get here. the better it is.