Solid and plasticised state bonding developments are allowing the improved and lower cost fabrication of laminates and welded constructions of steel and aluminium and other hard-to-join metal combinations.
US-based companies seem to favour improved roll bonding, while concerns in the UK and Russia seem to favour friction welding. Both approaches have their merits and demerits, but achieve the same objectives: high temperature enduring fabrications that combine properties – especially good heat transfer through aluminium with the strength of carbon steel or the corrosion resistance of stainless steel. Potential beneficiaries of these processes range from nuclear reactor components to domestic cookware.
Eureka's interest arose from two separate sources. The first was coming across cookware, made by US company Calphalon, which purported to be made from laminated stainless steel/aluminium sheet. The second was a meeting with Russian scientist Dr Yuri Kostin, of the St Petersburg-based company Prometey http://www.prometey.nw.ru.or email vvv@prometey2spb.su. Both parties flatly refused to give details of their processes, except that Dr Kostin said that while it is relatively easy to produce thick aluminium-steel sections, the real trick is to be able to produce thin laminates with 3 to 5mm thickness of steel and 4 to 7mm of aluminium. Prometey's aim, in the latter case, is primarily to facilitate the welding of aluminium superstructures to steel hulls in ship building. He said his company could also clad austenitic stainless steel to carbon steel without cracks, and make various other fabrications from combinations of dissimilar metals by friction welding.
The problem in all cases, is to avoid the formation of the brittle intermetallic alloy FeAl3. This requires working at temperatures well below any melting points. Since successful manufacturing processes all seem to involve fairly secret proprietary techniques, we went to the horse's mouths on welding techniques, to ask how it is done.
Dr Amir Shirzadi, of the Department of Materials Science and Metallurgy at Cambridge told us that he had seen a stainless steel saucepan with an aluminium plate bonded to its base at the Federal Armed Forces University in Hamburg. He said he had been told that it had been made by a high pressure diffusion bonding process close to forge welding.
John Weston john.weston@twi.co.uk , of TWI, www.twi.co.uk just down the road from Cambridge said: "Such joints are normally made by rolling, explosive bonding or by friction techniques. We are not sure of the details of the rolling techniques, but in all likelihood the sheets of stainless steel and aluminium are welded within a container (possibly evacuated) and then hot rolled. You might try Spur Industries of Spokane, Washington, for more information."
Rick James, rick.james@spur-ind.com the president of Spur Industries www.spurind.com told us: "Our process is roll bonding. We are small enough that every part has several inspections, so we compete with makers of large clad plates on cost, quality and yield. We specialise in aluminium on steel, aluminium on stainless steel and aluminium on copper. We also do aluminium on titanium, aluminium on brass and other speciality items for specific customers.
"Roll bonding or bonding by rolling together two metals is done in a variety of ways. Certain process parameters are advocated depending on the size of end parts, the finish gauge determining whether it is clad plate, bar or sheet or foil. Our process is geared to produce smaller parts ready to weld or machine, cost effectively. The specifics of our actual process steps and our unique preparation technologies would be inappropriate in this response."
Bend test of slice of part roll bonded by Spur Industries
