How to best join aluminum: Fasteners, brazing, soldering or welding?

J.G.
By J.G. Pasterjak
Jan 7, 2024 | aluminum, Welding, Shop Work | Posted in Shop Work | From the Oct. 2020 issue | Never miss an article

Photography Credit: Weldscientist

Anyone who’s ever had a track car has probably done some aluminum fabrication. Whether that was a simple hand-formed bracket or a more complex structure, aluminum’s low cost, ease of availability in big-box stores, high strength-to-weight ratio and mostly benign nature make it the perfect material for even the novice fabricator.

But when it comes to joining two pieces of aluminum, …

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Comments
Larry
Larry New Reader
12/1/20 9:19 a.m.

What about bonding? That is the preferred method of most manufacturers now. And it is being done by many body shops.

As heat weakens tempered Al and the bonded surface spreads out loads, the joints tend to be stronger. I would love to see more about DIY/grassroots bonding applications. Comparing things like Hysol /Loctite E-60HP and 3M 7333, ease of prep, application, strength, etc.

captdownshift (Forum Supporter)
captdownshift (Forum Supporter) GRM+ Memberand UltimaDork
12/1/20 9:36 a.m.

Fun fact, most hvac duct work is aluminum. Duct tape is clearly the answer. 

jimbbski
jimbbski SuperDork
12/1/20 11:07 a.m.
Larry said:

What about bonding? That is the preferred method of most manufacturers now. And it is being done by many body shops.

As heat weakens tempered Al and the bonded surface spreads out loads, the joints tend to be stronger. I would love to see more about DIY/grassroots bonding applications. Comparing things like Hysol /Loctite E-60HP and 3M 7333, ease of prep, application, strength, etc.

This can work for some joints but not all.  You need surface-to-surface contact to have a strong bond and many times you don't have that. When designing  a part this can be taken into consideration but for one off parts you're making and if weight is a consideration I'd go with a welded joint.

wae
wae UberDork
12/1/20 11:32 a.m.

For a project I just completed, I had a need to bond aluminum roofing flashing to steel angle iron.  There is no space on the inside for a fastener or rivet to stick out so I needed something flush.  In retrospect, I could have drilled and tapped the steel and then used a very short machine screw, but that idea came late.  I used a Loctite construction adhesive on one (PL-375), DAP construction adhesive (Dynagrip MAX) on two, and just regular silicone on one.  They all worked pretty well, but due to the long cure times, clamping is required.  Where I couldn't clamp things properly, I got some pull-back from the springiness of the flashing, but other than that it is pretty solid.  It isn't structural, and I haven't tested it to see exactly how much force it would take to pull the skin off, but it worked pretty well and was quite cheap.

Shaun
Shaun Dork
12/1/20 12:38 p.m.

Really really good double sided tape and rivets has worked for me.  

Larry
Larry New Reader
12/1/20 1:00 p.m.

In reply to wae :

This brings up a good point. For many of us, we will be adding aluminum to a steel structure or composites to an aluminum structure to reduce weight. Welding will not work there, and bonding is stronger than mechanical fasteners. 

While it will not work well for some joints, for joints with the needed surface area, bonding ends up being stronger and lighter than fill rod or solder (spot welds do not add filler, but are not as strong). Panel bonding is very common place now, but structural applications keep growing. 

BA5
BA5 GRM+ Memberand Reader
12/1/20 1:48 p.m.

Bonding with rivets works well, the two methods pick up the slack in the weakness of the other: bonding helps distribute the load over a larger area than rivets generally are able to and can resist loosening over time.  The rivets can help resist peeling and delamination, which is the weakness of a bonded joint.

Djtilly
Djtilly New Reader
12/1/20 4:06 p.m.

You missed solid rivets - The mainstay of old school monocoque racing cars and aircraft.  Biggest con is, of course, that you need access to both sides of the joint.

Leif_In_Calif
Leif_In_Calif New Reader
12/1/20 9:34 p.m.

Also forgot gas welding...the way all those cool cars in the 50's were built. It takes a little practice but the equipment isn't expensive.

frenchyd
frenchyd PowerDork
12/1/20 10:27 p.m.
BA5 said:

Bonding with rivets works well, the two methods pick up the slack in the weakness of the other: bonding helps distribute the load over a larger area than rivets generally are able to and can resist loosening over time.  The rivets can help resist peeling and delamination, which is the weakness of a bonded joint.

3M makes a wonderful bond with the side of rivets. The problem is I use Cleco's as an alignment tool but doing so means some seepage invariably gets on the Cleco's. I haven't found anything that gets the 3M stuff off so it's use em & toss em'.  Expensive. 

I've for non racing applications used mostly pop rivets and a pneumatic riveter to go fast enough to  avoid letting the bond set up before finishing. 
Since some aircraft applications allow "pop-rivets" maybe I shouldn't be so picky.  

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