I have a Mercury Outboard engine with a cast aluminum lower unit. In 2015 a drunk pulling into the parking lot hit my lower unit with his boat. Among other things the collision broke a piece of the anti-cavitation plate off the lower unit. It's maybe 1" x 2" piece. I still have the piece. I still have the Mercury outboard. What's new is I have a tig welder.... and I'm kinna sorta getting to where I can make consistent aluminum welds. That's because, in part, I have a truck load of 1/8" aluminum stock which has afforded me virtually unlimited practice. I have no cast aluminum to practice on....
Sooooo.... I suppose my first question is "Does cast aluminum pool like, say, 6061 T6?" If it doesn't how do I know it's ready to accept filler? If it does is it similar to welding 6061? In house I have 4043, 5356, and 4943 filler in both 1/16" and 3/32". The piece is 1/8"-3/16" thick. Based on what I've read I would use 4943 for this repair. This part sees no heat at all. I will 'V' it and clamp it into postion. I have no intention of removing the lower unit as this repair is on the most distant piece of the anti-cavitation plate and the lower unit its-self is a rather large heat sink. I have access to both top and, by tilting the engine full up, the bottom. Although the bottom will be somewhere around a 45 degree angle - but do'able. Other than excessive cleaning/prep what else should I know about welding cast aluminum. Obviously this piece is not critical to the operation of the boat or engine being as it's been broken for over 5 years but I just thought I fix it if I can..... Thanks!
Clean and remove all the paint in the area. Really well. Preheat the patent metal to help purge any embedded impurities before welding. Then clean again.
I like 4943 or 4047 for that repair. Definitely 3/32. Several tacks top and bottom to keep piece from pulling during the welding. Weld in short runs, 2” or so. Stop, relocate, short runs switching top and bottom to keep the piece as straight as possible. I’d suspect 2 passes should do it. Lots of heat on initial pass with good penetration: 50-60Hz, 65% balance for lots of cleaning, and crank your machine up in amps.
For a second pass, 100-120Hz, 72% balance, and cover it. Let the root pass cool first and clean it again before covering. Grind flush after it cools. Do it right, it will never be detectable and the harmonics will be perfect! And if it goes badly, stop, cut it loose, and start over. It’s only metal
2 caveats: that piece of aluminum backer will absorb some of the amperage (heat) so you’ll need to crank up a tad more than you think. Also, be careful not to weld it to the cav plate
I use stainless in that application because it won’t weld to aluminum and it keeps the heat in the weldment.
Dang.... I started to use stainless there but thought.... nah. But it didn't weld to the cav plate. Now... My initial settings were 180a, 50freq., 60cleaning. I'm using a #5 cup with ~12 cfh. Wellll.... I'm doing my first spot weld and hammer down on the amperage. Almost blew the corner of the back of it. Mmmm... seemed a tad hot. Tried it again with a little less pedal and still was blowin' things up. So upped the freq. from 50 to 80 and that made it manageable. But even at that I had to go real light on the pedal or I was gonna blow more holes in it. As you can imagine it was pretty fugly. I didn't get a picture of fugly but in the end I had to carbide burr a groove where the break was in an attempt to clean it up. After that it looked like this...
Then I cobbled some more 4943 on it. This cast is reeeeeeeel sensitive to amperage it simply will not take much heat. Any way I walked the filler around some filling in the groove. Ended up looking like this. 20200609_154857 by Doug Wei, on Flickr
Didn't get it all done but I'm letting it cool right now then I'll grind it down , clean it up and put what I hope will be some finishing filler on the trailing edge. The weld penetrated all the way to the underside such that I'll be grinding some there to clean it up. Then I'll see what that looks like. Might probably will be putting a little filler on the underside.
You can always run a carbide burr to remove the ugly, then give it a good wire brushing (only brush in one direction, it helps keep it just a smidge cleaner), acetone wipe, then go at it again when it's cold so you can build up the edge, or clean up the bead.
Here's the final results... I'll have to fill some pits with a filler called 'All Metal'. It seemed like no matter what I did more of those stinkin' voids/pits would pop up. But all in all I'm pleased with the way it came out....
Those pits are porosity and air trapped in the casting. That’s the real trick to cast aluminum; you throw heat at it and the air pockets expand and blow out. Before grinding, you can wash that weld with your torch, no filler. If porosity surfaces, let it cool. Then spot fill with light wire. Let cool. Move around and add filler where needed.
The beauty here is that you only need to insure your weld is strong. Grinding afterwards will make it pretty. And that cav plate does need to be shaped and smooth to function so grinding is perfectly acceptable.
Sorry I missed this thread. I just did three of those in the last two weeks. There is a company out of texas that makes fine repair blanks for those if you loose the broke piece. I use 5356 filler. Seems to do the best for me. Some merc castings are dirty but they are all better than volvo or brp. Those seem to have more mag in the mix. Merc seems to weld cleaner. I do a pass with no filler on mercs and high cleaning action. 65 percent or so on my dynasty. That boils out the smut. Then a light buttering pass where I try to just get a little filler on each side smooth like. Then weld it up. Fair it out, rough it, prime with self etching primer and paint.
Miller Dynasty 280 DX, Lincoln 210 MP, More tools than I have boxes for and a really messy shop.
OK.... so I'm going back and fill the porosity. After double checking I had a low area on the bottom on the trailing edge that needed work so I figured might as well do it right vs good enough. Heck might still end up with 'good enough' took some doing to chase the porosity away but 'I think' I got it. Waiting to cool/grind then I'll see if I'm done - or not.
Well... in the end I had to settle for "good enough". I chased that porosity all over the plate. The repair area just kept getting bigger n' bigger. I decided to cut my losses and put a glaze coat on it to fill what few porosity remained both on the top and on the bottom. The underside got kinna scared up when I put a block of wood under there to re-install the prop. But... it is what it is. I like the way it came out looks way better than it did. Might even help the boat get up n' over coming outta the hole!
cj737 wrote:Looks darn good for a first go with cast! Congrats-
Thanks! Yeah... I learned a bunch. #1 Don't mess with cast aluminum!
Actually that's not true. I missed a couple of steps that would of probably made it easier.
Didn't preheat
I only sorta kinna made cleaning passes with the torch before going at it with filler rod.
When you're working with cast aluminum that's only 1/8" or so thick you can't get it done in one pass, or two passes, or....
But it's done and based on investment(s) that li'l repair only cost 5k!
and I'm kinna sorta getting to where I can make consistent aluminum welds. That's because, in part, I have a truck load of 1/8" aluminum stock which has afforded me virtually unlimited practice. I have no cast aluminum to practice on....
