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OT? GM is spot-welding steel to aluminum!

Detroit newspapers have recently featured a story about GM's new technique for spot-welding steel directly to aluminum, eliminating several pounds of rivets per car.

No mention was made of how they avoid corrosion due to galvanic action. No luck on Google either. Any ideas?

Best regards,

Bob Masta DAQARTA v9.20 Data AcQuisition And Real-Time Analysis

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Reply to
Bob Masta
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Won't there still be galvanic action with rivets?

(Email the newspaper/reporter maybe they can provide the source?)

George H.

Reply to
George Herold

In theory you could paint the panels before riveting, and use painted rivets. That should hold until the vehicle is out of warranty.

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Tim Wescott 
Control systems, embedded software and circuit design 
I'm looking for work!  See my website if you're interested 
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Reply to
Tim Wescott

Greetings Bob, Aluminum and steel are commonly explosively bonded for use in the marine industry. One of the terms for this material is "Transition Bar". It is used, for example, when an aluminum superstructure is attached to the steel deck. Besides being a faster attaching method because the bar is welded to each structure instead of bolting or riveting, this method of attaching has several other advantages, one important one being the elimination of corrosion at the aluminum/steel interface because there is no chance of an electrolyte in the joint, as there would be in a bolted or riveted joint. Of course if the joint was underwater the aluminum would corrode much faster than the steel. I would think the spot welded joint in the cars would act the same. Eric

Reply to
etpm

Thanks, Eric. I hadn't considered the fact that with a weld there could be no electrolyte in the joint. If GM is using this for joining panels that aren't exposed directly to road salt, etc, then there wouldn't even be any droplets to bridge across the weld edges. I suppose for underbody use the panels would be coated after welding anyway, so even better protection from electrolytes.

Best regards,

Bob Masta DAQARTA v9.20 Data AcQuisition And Real-Time Analysis

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Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE 8-channel Signal Generator, DaqMusiq generator Science with your sound card!

Reply to
Bob Masta

Greetings Bob, You're welcome. Some years ago I got curious about the stuff when my neighbor gave me a chunk of transition bar. When the metals are joined they ripple at the interface and these ripples cause the two metals to physically interlock which provides a really strong mechanical joint. The size and wavelength of the ripples can be controlled by the amount and type of explosive used. The explosion is started at one end or corner of the sheets or plates being joined and the rippling of the surface drives surface contaminants ahead of the waves, resulting in a very clean joint. Sometimes two metals can't be joined reliably so a third metal is sandwiched between the two. I have a chunk of aluminum, niobium, titanium that was explosivly bonded. The transition bar I have shows clearly how the waves of metal interlock, with one wave curling around the other. The spot welded metals you posted about intrigue me because the joining process is different. Now I need to look it up to see how it works. Cheers, Eric

Reply to
etpm

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