Material Handling and Welding, Brazing, Soldering
Materials, heat and joining
Material handling begins with identification: alloys must be traceable by marking, batch and certificate; heat-treated parts must not be centre-punched or engraved in a critical area; sheet is stored on edge, clean and protected; composites are kept in the specified freezer and out of sunlight. Observe shelf life (sealants, adhesives, primers, hoses, elastomers), keep parts in quarantine until inspected, and avoid contact between dissimilar metals such as aluminium and steel or carbon and aluminium, which drives galvanic corrosion.
Know the joining processes and their boundaries. Soldering melts filler below about 450 °C without melting the parent metal; brazing uses filler above 450 °C, also without melting the parent; welding melts the parent metal. Know oxy-acetylene flames (neutral, oxidising, carburising), TIG for aluminium and stainless, MIG for thicker sections, and resistance spot welding for sheet. Aluminium needs flux or an inert atmosphere, and flux residues are corrosive and must be removed.
Know the defects questions test: porosity, slag inclusion, lack of fusion, undercut, cracking and distortion; the heat-affected zone as the weak region; stress relief after welding; and inspection by visual, dye penetrant, magnetic particle, ultrasonic and radiographic methods. Welding near fuel tanks, fuel lines or sealed structure requires fuel-system isolation and a hot-work permit.
Traps: assuming brazing is a structural repair for every alloy, leaving flux on the joint, welding a heat-treated alloy without an approved procedure, and soldering aircraft wiring in high-vibration areas.
Rule of thumb: 450 °C is the soldering/brazing line - below is soldering, above is brazing, and only welding melts the parent metal.