Author Topic: Aluminium Brazing  (Read 8228 times)

Offline tangler

  • Full Member
  • ****
  • Posts: 777
  • Christchurch, UK
Aluminium Brazing
« on: July 27, 2013, 12:24:36 AM »
As you may be aware from my Wyvern build, I'm looking to insert an aluminium plug into the cylinder head in order to rectify a machining error.  I've done some experimenting with HTS-2000 ally brazing rod from http://www.aluminiumrods.co.uk/.  What I was interested in was how well the braze would fill the gap between  a plug and its hole.  A hole and plug were machined from scrap aluminium alloy, the plug was a sliding fit in the hole with little play.  Plug and hole were both turned without coolant to minimize contamination of the surfaces.  The brush and rod are both stainless steel, used to agitate the braze when molten.



The square with the hole was heated with a handyman type gas torch first until the braze rod melted when touched on it with the flame absent.  With some molten braze in the hole I stirred it around a bit with the stainless steel rod.  The plug was then heated and I managed to apply a few blobs of braze onto the shaft of the plug.  I then assembled the plug on top of the hole but the braze had solidified so it was actually balanced on top.  Re-application of heat allowed the plug to slide into the hole.  I was surprised how easily it slid in considering the gap was pretty small.  The end result looked like this.



When cool I used a hacksaw to section the joint, turned it flat in the lathe and polished it on some 1200 grit wet and dry paper with water as a lubricant. You can clearly see the difference between some voids at the top of the hole/bottom of the plug and the braze. 




I was very impressed by the penetration of the braze through the whole length.  Here's a micrograph of the top, again showing what is void and what isn't. Also visible is the way the braze has filled the slight under cut I made to ensure that the plug would sit flat.



And this is a continuation of the braze line.  At certain angles the braze shows up as a brighter line, demonstrating that it is not void.



I'm impressed.  It was very easy to use.  The next step is to try it out on a bit of the head casting.  There's a bit of spare on the chucking piece so I'll use that - the characteristics of the cast metal may be somewhat different as it has probably got a significantly higher silicon content than the wrought alloy.



Offline smfr

  • Full Member
  • ****
  • Posts: 1195
  • San Francisco Bay Area, California
Re: Aluminium Brazing
« Reply #1 on: July 27, 2013, 01:58:24 AM »
Very interesting, and I like your detailed analysis of the join. I was just thinking about using some of this stuff to build up a base for a barstock engine.

Simon

Offline Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12696
  • Hampshire, england.
Re: Aluminium Brazing
« Reply #2 on: July 27, 2013, 07:05:56 AM »
Worth bearing in mind  :ThumbsUp: thanks Rod.

Jo
Usus est optimum magister

Offline tel

  • Administrator
  • Full Member
  • *****
  • Posts: 1657
  • Bathurst District, NSW, Oz.
Re: Aluminium Brazing
« Reply #3 on: July 27, 2013, 08:52:49 AM »
Very timely - I have an ali brazing job coming up in the not too distant future and it's had me scratching my head a bit, thank you!  :ThumbsUp:
The older I get, the better I was.
Lacerta es reptiles quisnam mos non exsisto accuso nusquam

Offline cidrontmg

  • Full Member
  • ****
  • Posts: 18
  • Penafiel, Portugal
Re: Aluminium Brazing
« Reply #4 on: July 27, 2013, 12:12:35 PM »
Interesting. "Buy Aluminium Brazing Rods - Please contact us if you wish the order to be delivered outside the UK Mainland." OK, can be done. And "Aluminium Rods - Pack of 10 Rods, 29.95, Each rod is 18" in length (+/- 45 cm)." OK, but how's the thickness of the rods? Seems it's thicker than 2 mm, doubtful even 3 mm - assuming it's 2.5 mm. Not exactly cheap, but silver solder is way more expensive. E.g. Cupalloys, 455 Silver Solder 2.5mm dia x 500 (2 rod pack), at 35.97. Silver solder works usually with quite narrow spaces, 0.05 mm, same as HTS2000 aluminium brazing, but almost nobody works with silver solder repairing and filling a broken and lost bracket, or a filler for thin material, porous, or even cracks and holes. Fascinating.   

Offline tangler

  • Full Member
  • ****
  • Posts: 777
  • Christchurch, UK
Re: Aluminium Brazing
« Reply #5 on: July 27, 2013, 02:18:50 PM »
The rods are oval in cross section approx 1.9 x 2.4 mm.  Not cheap but way less than the stuff that some guys from Germany have been pushing at the last few ME exhibitions I've been to.

I've done a bit more experimentation.  This time a 1/4" wrought aluminium rivet into a piece of cast aluminium.  I purposely made the fit sloppy, about 5 thou on diameter,  to test the gap filling properties.  I vaguely tinned the hole and put some blobs on the stem of the rivet.  I may have overheated the rivet - I thought I saw some crinkling of the surface but wasn't sure. 

This is a transverse cross section.  Gap filling isn't great.  The splodge in the centre may be evidence of over heating.





This longitudinal cross section shows more evidence that the rivet was over heated since it looks like the blobs have eaten into the rivet.  However they have filled those gaps.  What is reassuring is that the cast alloy, which is the outside material,  appears to have behaved very well.



One more test I think:  Back to about 1 thou clearance.  I'll try and tin the hole by stirring the braze around with the stainless steel rod but I won't pre-tin the rivet.

 

Offline chucketn

  • Full Member
  • ****
  • Posts: 394
  • East TN, USA
Re: Aluminium Brazing
« Reply #6 on: July 27, 2013, 02:38:49 PM »
Very interesting, tangler. Thanks for posting the details of your experiments.

Chuck

Offline steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 10328
  • Central Massachusetts, USA
Re: Aluminium Brazing
« Reply #7 on: July 27, 2013, 02:57:21 PM »
What is the flow temp for this alloy?

Heat treated alloys like -T6 will loose their temper, and some of their strength, at about 360F....so be careful what you use this for.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline tangler

  • Full Member
  • ****
  • Posts: 777
  • Christchurch, UK
Re: Aluminium Brazing
« Reply #8 on: July 27, 2013, 04:20:29 PM »
They claim the working temperature is about 400 Celsius so I agree, caution is called for.  A search seems to bring up quite a lot of comments from the boating community.  I would have thought it would be difficult to use on large structures since you would need to locally heat to 400C which is difficult to achieve on a good conductor like ally.  The suppliers recommend using a MAPP gas torch on big stuff.

Rod

Offline tangler

  • Full Member
  • ****
  • Posts: 777
  • Christchurch, UK
Re: Aluminium Brazing
« Reply #9 on: July 27, 2013, 05:51:26 PM »
One more attempt.  Rather inconclusive.  Penetration doesn't look great but the bond is firm.  I think its gas tight.  I'll go back to trying to tin both parts and I think it would be good to try and rotate the plug while the braze is still liquid.  A new cylinder head is on it's way from Hemingway so I can mess this one up completely.  So, pros and cons over JB Weld?  JB would be much easier to use but might be a thermal barrier and might break down at  operating temperatures.  Ally braze is obviously trickier but is good for 400C and good thermal contact.





Thats enough R&D for now,
cheers,
Rod

Offline Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12696
  • Hampshire, england.
Re: Aluminium Brazing
« Reply #10 on: July 27, 2013, 06:06:01 PM »
Must be time to try on the Wyvern head   :ThumbsUp:

Jo
Usus est optimum magister

Offline tangler

  • Full Member
  • ****
  • Posts: 777
  • Christchurch, UK
Re: Aluminium Brazing
« Reply #11 on: July 27, 2013, 06:34:02 PM »
I'll give it a go tomorrow.  I think the key to success is to make sure I can hold everything firmly while hot so I can scratch the surfaces with the stainless steel rod, which spreads the braze.

Rod

Offline smfr

  • Full Member
  • ****
  • Posts: 1195
  • San Francisco Bay Area, California
Re: Aluminium Brazing
« Reply #12 on: July 27, 2013, 07:23:12 PM »
http://www.aluminiumrods.co.uk sings the praises of HTS-2000 over other Al brazing products like Dura Fix http://durafix.com and Aladdin 3-in-1 http://www.aladdin3in1.com/products/3in1rod.php, but has anyone in the US tried any of the Al brazing products on this side of the pond? The only more "advanced" product I could find was HTS-735-II, for sale here: http://www.weld-aluminum.com.

Simon

Offline Don1966

  • Full Member
  • *****
  • Posts: 5999
  • Morgan City, LA (Along the Gulf Coast)
Re: Aluminium Brazing
« Reply #13 on: July 27, 2013, 07:42:30 PM »
Simon I have used the DURAFIX rod but I don't remember exactly which one. The surface has to be clean and the rod not to be in contact with the flame. You can actually plug a hole in an aluminum can with it. I had also experimented brazing a cup bottom, but couldn't get a good seal, I always had leaks.

Don

Offline Marinus

  • Full Member
  • ****
  • Posts: 159
  • Limpopo, South Africa
Re: Aluminium Brazing
« Reply #14 on: July 27, 2013, 09:39:36 PM »
That looks like great stuff. My dad gas brazed an alu magneto cover for a friend with just normal alu rods! He had to grind it with the dremel afterwords.
Kind regards

Marinus Kruger

Offline ScroungerLee

  • Full Member
  • ****
  • Posts: 299
  • Southwest Connecticut, US, North America, Earth
Re: Aluminium Brazing
« Reply #15 on: August 10, 2013, 08:56:57 PM »
I have tried this with cheap aluminum rods, I am not in the shop to get the exact brand.  The most critical part seems to be the scratching during application to scrape down to clean aluminum while the molten rod is on that surface.  For example, when tinning your parts I would get the blobs onto the plug and scratch the plug with the stainless brush instead of the metal scraper.  That will spread the tinning nicely over the whole part.  Do that while the rod material is molten and it should adhere very firmly and fill voids.

Another thing no one mentioned is that the rod material is substantially harder than the original aluminum so some care may be needed when finishing whatever you are working on.  Probably not an issue with what you are attempting to do.

Hope that helps,
Lee
Mmmmm.... Shiny!