Explosion welding, also called explosive cladding, joins two metals together by an explosive force. It is often used to join dissimilar metals that have a significant difference in mechanical properties, thermal expansion coefficients, or melting temperatures — such as a low-cost metal to a more expensive corrosion-resistant metal. Some of the common clad layers deposited onto steel plate are aluminum, copper, bronze, titanium, monel, nickel alloys and zirconium.
An explosive weld is made by impelling a cladding plate against a substrate plate using significant energy from an explosive discharge, which results in a high energy rate impact. Very high forces at the impact area (estimated at several hundred thousand lb/in.2) cause the first few atomic layers of each material to form a plasma jet that is ejected out of the impact zone, taking with it any contamination and unwanted oxide layers. The impact causes the metals to form a true metallic bond, where the metals share valence electrons.
Of particular importance are the characteristics of the explosion weld itself. Explosion welding traditionally produces a wavy bond zone morphology. This waviness is a function of the different material properties and the welding parameters used. Impact angle and the detonation velocity influence the amplitude of the waviness.
When properly made, an explosion weld is a solid-state bond without any heat affected zone to degrade its strength, as is typical of other heat-dependent welding or joining processes.
Explosion welding is well-suited for joining large, flat areas, as in clad plate manufacture. To get more complex components, a bimetal preform is typically produced by explosion welding in the plate or tube configuration, followed by hot or cold working.
The explosive welding technique is frequently used to clad low cost plate (usually carbon steel) with more expensive corrosion resistant materials. This clad plate is typically used as tube sheet for heat exchangers in the chemical and petrochemical industries. Other applications include sandwiched metal for coinage and the production of titanium-to-stainless steel transition joints in the Apollo spacecraft.
A broad range of sizes can be explosively welded; it has been used to join electronic components of widths less than 0.5 mm and for cladding plates up to 5 x 12 m. Cladding metal thicknesses can range from 0.025 to 100 mm (0.001 to 4 in.), and base-metal thickness can range from 0.025 mm (0.001 in.) to over 1 m (40 in.). The size limits are generally mandated by component metal manufacturability and transportation requirements.
Because of the unique safety and noise-vibration considerations, explosion welding is usually performed in isolated facilities by experienced companies.
Advantages of explosion welding:
• Large areas can be bonded quickly
• Stronger bonds than friction and diffusion welded joints
• Requires knowledge of explosives
• May require special licensing for high explosives
• Limited to flat surfaces or coaxial cylindrical surfaces