Welding Aluminum to Steel

[KENAT]

Not sure this is actually the right forum, and this isn't a directly work related question but...

Saw this article about how GM has refined welding Steel to Aluminum to address strength issues etc.

http://www.msn.com/en-us/autos/news...-ford’s-bet-on-aluminum/ar-BBtqCUf?li=BBnb4R5

However, for automotive applications I'm still wondering about the durability re. corrosion etc.

Any thoughts or comments?

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[metengr]

You may find this interesting. I also looked at FSW as the main process for joining steel to aluminum.

http://www.gizmag.com/honda-steel-aluminum-welding/24096/

 

[weldstan]

Properly coating the aluminum and steel interface will mitigate the corrosion concerns.

 

[FennLane]

I generally believe that the challenges this will create my become quite significant.

I successfully friction welded Aluminium to both normal steel and stainless steel back in the early Seventies.

To suggest that a 'glassy' film is produced due to melting the aluminium is not quite sufficient data.

Due to the difference in electronegativity between these two metals there is a significant tendency for the formation of a Laves Phase (Hume-Rotheray Rules). If the film at the interface is continuous than the weldment will inevitably fail if any shear stress is present.

The thickness of the film makes little or no difference to the strength but if the film can be broken up then bonding between the steel and the aluminium can occur and reasonable strength levels can be produced.

Welds of this type seem to be more tolerant of simple tensile rather than bending stresses.

By using a solid phase process such as Friction or Friction Stir Welding breaking up this film by controlling the deformation mechanisms in the Aluminium become feasible and reasonable mechanical properties can result.

I am not sure how much coating surface prior to welding will affect results but in my experience of Friction welding cleanliness and lack of surface contamination was essential.

If you want to see the impact of bi-metallic corrosion on steel/aluminium structures just look at the horror stories of restoring any Zagato Superleggera bodied car such as an Aston DB4.

It is also interesting to see Honda making claims about the development of FSW which I always though was a process developed by MTS in the States - still you live and learn.

 

[drawoh]

KENAT,

Aluminium and mild steel are fairly close on the galvanic corrosion chart. Perhaps everything could be zinc plated.

--
JHG

 

[dvd]

I'd like to see the fatigue test data on this.

 

[KENAT]

Just seems like for Automotive they'll have to be careful about where these dissimilar metal joints are so that any protective coating doesn't get worn off/damaged.

Also, what happens after a crash - does the repair shop need special equipment? Or are they forced to replace entire panels every time etc.

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[berkshire]

Years ago we used to TIG weld aluminum to steel as a " party trick " however the joint was really a form of soldered joint.
It may be possible at the shop level to spot-weld two components together, but I feel it may require a more sophisticated spot welder with ramp up, and ramp down, controls, than most body and fender shops have.
B.E.

You are judged not by what you know, but by what you can do.

 

[racookpe1978]

Many dozens of years ago, the US Navy built several classes of ships with steel hulls and aluminum superstructures: This gave a flexible and weldable hull (to bend in the seas and storms) and a light superstructure (to save weight and to reduce rolling problems and increase weapons and radar payloads up high above the waterline.)

The method worked, but it was essentially four very long explosive-formed joints of the two metals at the deck level: Al above, Fe below the joint. The joint was ultra-cleaned and closely machined to near-zero tolerance between the two, then everything was placed between two long explosive-ropes (det cord variety I think). They blew up the det cords, and the two metals were molecularly joined by the sudden force jamming the crystals into each other. No melting really. Think of a forged type "hit" .

Don't know about corrosion properties - but you'd figure the Navy would paint everything. And add even more weight and fire hazard from the paint added every year.

 

[EdStainless]

For the Navy work they explosively bond thick plates and then saw cut the transition strips out of them.
Steel plate setting in a bed of sand, the Al plate supported by little plastic spacers (LDPE), a wood or cardboard box around the whole thing to contain the 2"-4" of AnFO on top of it, and a det in one corner.

The spot welds that I have seen are actually not melting either metal, but getting them hot enough to be soft enough to 'forge' a joint.
If either metal actually melts you will form very brittle intermetallic compounds.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[DVWE]

Found this article interesting...

https://www.asme.org/engineering-to...ew-welding-process-joins-high-strength-metals

 

[KaelYAH]

I've read this thread, seen the site, and I have to say
simply - two different metals, as a welder for 10 years, engineering for 7 years, in my expert opinion the two cannot be 'alloyed' so

 

[SwinnyGG]

"I've read this thread, seen the site, and I have to say
simply - two different metals, as a welder for 10 years, engineering for 7 years, in my expert opinion the two cannot be 'alloyed' so"

Techniques for bonding steel and aluminum to each other have existed for quite some time now- so-called 'explosive welding' being discussed for shipbuilding is one of several ways to do it.

However, it is only in recent years that is has become inexpensive enough to use in automotive applications.

 

[Guest102023]

Body repairers are having nightmares.
Looks like Ford has truly bit the bullet; 700 pounds is a great leap forward after decades of mostly talking and only nibbling away at the weight problem in vehicles.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"