Friction welding is an ideal method to join dissimilar metals- cost, quality, and strengthwise.

Ideal for dissimilar metals

Here are 7 advantages of Friction (inertial) welding:

  1. Easily joins dissimilar metals. This means the ability to use more expensive corrosion resisting materials where needed, and less resistant but sufficiently strong materials where there is no need- ON THE SAME PART.
  2. The full surface of the cross section is made up of both metals, airtight and absent of voids.
  3. Friction welds are higher strength than other means of joining.
  4. Friction welds often cost less as there are no consumables like filler metals fluxes etc. (This would be the bottom line for most businessmen, but I chose another, see # 7 below.)
  5. Friction welds minimize the Heat Affected Zone (HAZ).
  6. Friction welding minimizes the need to clean  furnace residues from the entire part, post welding.
  7. The ability of a designer to optimize material choices by using friction welding cannot be overstated.

Airbag systems rely on friction welding for assembly.

I produced truckload quantities of 1050 modified steel for an automotive half shaft application, the friction welding process made this a highly reliable part despite the high carbon content and different material between the alloy steel  forged end  assembly and the  carbon steel shaft.
This welding process is ideal for pumps, process mixers, and other applications where a portion of the part needs to be food safe or chemically resistant, but the remainder of the part does not.  The photo below shows an electrical industry bimetallic (copper and aluminum) application.
Friction (inertial welding) lets the engineer put what s/he wants where they want it!

Frictional welding is a controlled  process where two components are frictionally bonded by the heat and mechanical displacement of each material’s being melted and re-fused amongst the melt products at of the other. The bond that is created by the mechanical intermixing and solidification of the two metals is strong and free from voids and porosity. It can be cost effective and offers design engineers many more options than other methods.
Friction or inertial welds are a key process for attaching precision machined components to other parts like shafts or bodies or forgings.
My thanks to Stuart Short at Inertia Friction Welding at IMTS for chatting with me about this not so well known joining process.
Airbag Dummy photo.

Any type of arc welding of resulfurized steels is generally avoided. This post will give you some  reasons why. Resulfurized steels are free machining steels. This includes steel grades in the 11XX and 12XX series,  such as 1215, 12L14,  1117, 1137, and 1144. These steels contain sulfur and may contain lead. These two elements will create low melting temperature constituents that will cause cracks.
Here are 3 reasons not to weld resulfurized free machining steels:

  1. Sulfur reduces weldability.  The higher levels of sulfur make a slaggy joint.
  2. The high volume fraction of manganese sulfides also hold hydrogen. This hydrogen can then create post weld cracking.
  3. Both sulfur and lead  can become a fume inhalation hazard at welding temperature.

Finally, with the exception of grade 1144, resulfurized steels are generally not sold to mechanical property requirements. Welding implies mechanical property performance.
We have seen 1215 welded using an inertial or friction welding process. But these welds are  usually not subject to mechanical loads, merely attachment. Here’s a video of a friction weld process for truck axles from Thompson Friction Welding in the UK.
Want a second opinion? Dave Barton at Lincoln Electric hosts a column   Barton’s Q&A in Welding Magazine published by Penton.  The second question in this column deals with welding 12L14.
Think of weldability and machinability as two sides of the material coin.

Heads it machines well, welds lousy, Tails...
Heads it machines well, welds lousy, Tails...

You can usually win on one, but at the expense of the other. If you need to weld, a low carbon plain carbon steel is your best bet.