Structural Aluminum (D1.2): Heat, Cleanliness, and Qualification
What the candidate must understand
D1.2 addresses aluminum structures, where thermal conductivity, oxide films, and heat-affected-zone softening drive every rule. Candidates should know the alloy and temper designations used in structural work, the filler-metal selection logic, and why aluminum demands dedicated, clean tooling. Understand the precleaning requirement: oxide removal and degreasing before welding, and wire-brushing with stainless brushes reserved for aluminum only. Know the qualification rules for procedures and welders, the essential variables (alloy group, filler, thickness, position, and current type), and the inspection acceptance criteria.
Traps in questions
A frequent trap is treating aluminum like steel: assuming the same preheat or the same postweld heat treatment. Aluminum generally does not need preheat and its strength recovery differs. Another trap concerns porosity: hydrogen is the dominant defect source, and moisture or hydrocarbon contamination is the usual cause, so answers blaming current alone are wrong. Watch for questions implying that a steel-qualified welder or steel procedure transfers to aluminum; it does not. Also expect confusion between heat-treatable and non-heat-treatable alloys when selecting filler.
Worked example / rule of thumb
Rule of thumb: clean, dry, and dedicated. If a stem describes porosity in aluminum, suspect contamination before machine settings. Worked example: a fabricator proposes using the same grinding wheel previously used on carbon steel. The correct reasoning is that embedded steel particles cause contamination and corrosion, so aluminum requires separate, clean abrasives and brushes; the answer is to dedicate tooling, not to increase cleaning time on shared tools.
Study approach
Build a table of alloy groups versus filler and note the essential variables. Review the cleaning sequence and the inspection criteria, then test yourself on why each rule exists.