Honda develops new technology to weld steel and aluminum together
A diagram of an Accord subframe made using the new welding process
Although some engineers have had success in spot welding steel and aluminum together, it has largely been considered impossible to achieve reliable, continuous welds directly between the two dissimilar metals. That changed last Thursday, however, when Honda Motor Company announced that it has devised a technique for doing that very thing. The results, which include lower vehicle weight and better performance, can be seen in the 2013 Accord.
The Honda team developed a variation on Friction Stir Welding, in which metals are joined via mechanical pressure – it's the same technique that has been used for experimental steel/aluminum spot welds in the past. As Honda explains it, “This technology generates a new and stable metallic bonding between steel and aluminum by moving a rotating tool on the top of the aluminum which is lapped over the steel with high pressure.” The welds that result are reportedly as strong or stronger than those made using regular Metal Inert Gas welding.
Steel/aluminum subframes built with the new technique are said to be 25 percent lighter than those made entirely out of steel, which should translate into improved fuel economy. The process also made it possible to alter the structure of the subframe, so that the mounting point for the suspension could be relocated – this change has reportedly increased the rigidity of the mounting point by 20 percent, and thereby improved the car’s dynamic performance.
Additionally, the new process uses about half the amount of electricity as Metal Inert Gas welding, and the machinery it requires isn’t as large as that traditionally used for Friction Stir Welding – in fact, it can be attached to an industrial robot. The technique can also be used for aluminum-to-aluminum welding, without any hardware changes.
A new non-destructive inspection system, incorporating an infra-red camera and a laser, is used to check all of the steel/aluminum welds.
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An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.
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I found this image from the wikipedia article to be a little more enlightening.
It heats the materials with friction and the rotating action of the tool mushes the two metals together
How is the corrosion from dissimilar metals addressed?
Thanks Wombat56 :)
Reference to Linked Article by MAZDA in 2005... (a form of stir spot welding Al to Steel.)
Use of Galvanised steel reduces corrosion... (zinc, so it may in fact be the zinc bonding to the aluminium, not the steel...)
Zinc alloy melting point ~420C
Zinc-Aluminium Alloy Melting point 400-600C
Aluminium Melting point 660C
Melting point Steel... 1370C
Phase change to alpha + austenite 738 C (to hot, for any of the other metals..)
Sure Stir welding does not melt the steel, it just heats it until it becomes plastic... (in the red range) which is, around the above chase change temperature....
Interesting that these materials are compatible.... have to be very careful not to overheat the aluminium....
However, hasn't stir welding been used for a while for welding dissimilar metals... (Often used to weld high strength steel shafts to cast iron, or to join castings.. or sifferent al/ Ti alloys... )
It appears that friction stir welding reduces the formation of the bad inter metallic compounds, which makes mig etc. welding of dissimilar metals a bad idea... This is most likely because it doesn't actually melt either of the parent metals (and doesn't transition the steel back to Gamma.), but plasticises them...resulting in a mixed phase, without the complete transition through the phases from solid to molten, as experienced by conventional welding... in the HAZ.
how is this diffrent and "new" from press welded aluminum topsides on steel hulled ships, as is widely been done for a long time
To answer the question about corrosion: There is a bead of sealant applied between the two metals prior to welding. And to answer the question about press welding: This process is modular and compact. The robot that does the work of FSW has virtually no foot print compared to all of the equipment needed for arc welding. This robot can be programmed to perform at any angle repeatable to +/- .0001mm. And also a side note: FSW can be performed at any orientation. Puddle control is not necessary so a vertical or upside down weld would not be an issue as it is in MIG/MAG welding.
I'm not convinced this process is immune to galvanic corrosion.
Steel-aluminum press welding on ships is protected by use of a sacrificial aluminum Cathode below the water level which corrodes, protecting the structure of the ship.
Galvanized steel makes no difference, as this is just a zinc surface layer protection, and a single bead of sealant is unlikely to prevent the intergranulization of the two metals which could lead to corrosion.
One way to resolve this might be to apply a small voltage to the aluminum, resolving the differing electrical potentials?
Otherwise, I don't see how these new Honda Accord subframes won't be falling apart after 20-30 years on the road.
The coefficient of expansion and contraction of aluminum and steel are quite different. How is the stress that will be put on the "weld" accounted for? There is also the electrolysis issue between dis-similar metals to consider.
@PeetEngineer: 20-30 years?! That's a long time for a car. Most cars don't last 20 years.
FSW of dissimilar metals isn't a new concept or unique to Honda...one of my college classmates did aluminum-to-titanium friction stir welds four years ago as an undergraduate design project.
As for the galvanic corrosion issue, there is no worry of corrosion in the weld itself because there is nowhere for the electrolyte to go. The surface of the weld (indeed, the whole piece) would need some sort of barrier coating, sacrificial anode, or other protection from the elements. No amount of galvanization or surface sealant would prevent any corrosion in the weld anyways, as mixing in the weld zone occurs up to two or three times the depth of the pin...welding a chunk of galvanized steel would simply drive grains of zinc into the center of the weld.
With the different coefficients of thermal expansion issue, I believe the exceptionally fine grain size (and resultant flexibility) of the weld itself would prevent the thermally-induced fatigue from causing problems. The friction stir process isn't just used for solid-state welding, it is also used to increase flexibility in stamped sheet metal - one pass with the friction stir tool along the areas of the greatest deformation reduces or eliminates tearing during the forming process.
Alloys are a mixture of dissimilar metals and as far as I know they don't corrode internally. Steel for instance is carbon and iron. I think that galvanic corrosion requires an electrolyte so it would be important not to have moisture at the interface but otherwise it seems it should work.
Brown's Gas can wield these metals together directly.
How does this compare with kelocouple? I find it very easy to use and very strong
I dont think Honda cares about twenty years down the road..... as for the cathode, if you look carefully you will (I think) see a place where there is space for this. Also tied to the cars electrical system makes it easy to control.....
Very interesting, more articles on this subject should be posted.If anyone wants to see some samples of tig welding aluminum to steel, go to you tube, punch in weld aluminum to steel, the first site shows a barrel loaded with scrap being lifted by a 1 1/2 piece of aluminum to steel . The user id is juaneno rc 4292. This is currently being developed for future release to the public. Most people don't realize that most of the issues raised are not problems as long as the designer takes the application needs into account !
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