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Can I Weld Aluminium to Steel?
Q: Can I weld aluminium to steel with the GMAW or GTAW welding process?
A: While aluminium can be joined to most other metals relatively easily by adhesive bonding or mechanical fastening, special techniques are required if it is to be arc welded to other metals such as steel. Very brittle intermetallic compounds are formed when metals such as steel, copper, magnesium or titanium are directly arc welded to aluminium. To avoid these brittle compounds, some special techniques have been developed to isolate the other metal from the molten aluminium during the arc welding process. The two most common methods of facilitating arc welding of aluminium to steel are bimetallic transition inserts and coating the dissimilar material prior to welding.
Bimetallic Transition Inserts: Bimetallic transition materials are available commercially in combinations of aluminium to such other materials as steel, stainless steel and copper. These inserts are best described as sections of material that are comprised of one part aluminium with another material already bonded to the aluminium. The method used for bonding these dissimilar materials together, and thus forming the bimetallic transition, are usually rolling, explosion welding, friction welding, flash welding or hot pressure welding, and not arc welding. The arc welding of these steel aluminium transition inserts can be performed by the normal arc welding methods such as GMAW or GTAW. One side of the insert is welded steel-to-steel and the other aluminium-to-aluminium. Care should be taken to avoid overheating the inserts during welding, which may cause growth of brittle intermetallic compounds at the steel-aluminium interface of the transition insert. It is good practice to perform the aluminium-to-aluminium weld first. In this way, we can provide a larger heat sink when the steel-to-steel welding is performed and help prevent the steel aluminium interface from overheating. The bimetallic transition insert is a popular method of joining aluminium to steel and is often used for producing welded connections of excellent quality within structural applications. Such applications as attaching aluminium deckhouses to steel decks on ships, for tube sheets in heat exchangers that have aluminium tubing with steel or stainless steel tube sheets, and for producing arc welded joints between aluminium and steel pipe lines.
Coating The Dissimilar Material Prior To Welding: A coating can be applied to steel to facilitate its arc welding to aluminium. One method is to coat the steel with aluminium. This is sometimes achieved by dip coating (hot dip aluminising), or brazing the aluminium to the surface of the steel. Once coated, the steel member can be arc welded to the aluminium member, if care is taken to prevent the arc from impinging on the steel. A technique must be used during welding to direct the arc onto the aluminium member and allow the molten aluminium from the weld pool to flow onto the aluminium coated steel. Another method of joining aluminium to steel involves coating the steel surface with silver solder. The joint is then welded using aluminium filler alloy, taking care not to burn through the barrier layer of silver solder. Neither of these coating type joint methods are typically depended upon for full mechanical strength and are usually used for sealing purposes only.