Aluminium is a strong but lightweight metal. Intelligently processed alloy forms then add desirable mechanical and physical features to the material, such as a talent for resisting corrosion. Looking closer now, we’re looking at the joints that secure aluminium parts. In particular, we’re about to delve into the testing procedures that cover aluminium welding. Look closer still, are there tiny holes in the weld?
When the welding equipment doesn’t shield a joint with enough inert gas, the aluminium gains a porous structure. The issue is sometimes visible to the naked eye, usually as craters and pinholes, but the worst part of this material defect likely resides inside the weld. Gas porosity is typically so finely embedded in the weld that it can only be detected by an ultrasound or radiographic test procedure.
Testing Open Surface Defects
Back at the pinholes and craters, the work looks amateurish, and a note may have to go into the welder’s file so that he can be retrained. In the meantime, how deep does the pinhole effect go? Spray dyes, visible or fluorescent, are pulled from the welding inspector’s toolkit. The coloured spray seeks out invisible discontinuities. As the liquid penetrant soaks into the weld, capillary action highlights the pits, reveals cracks, and adds definition to fusion flow lines. Inexpensive and easy to apply, it still takes skill to interpret the results of this visually-oriented weld test.
Employing Electronic Instrumentation
Visual inspections and liquid penetrants pick up hairline cracks, pinholes, and porosity issues. However, the only way to look deeply inside an aluminium weld is to use an instrument-based test procedure. Magnetic particle analysis is out because that technique is reserved for ferromagnetic metals. Called into service, the hardened case of a radiographic test device gets to work. Alternatively, the scope and handheld wand of an ultrasonic instrument bounce sound into the weld joint. Aware of the heat conducting nature of this popular alloy group, the weld discontinuities are conscientiously identified and recorded by the welding inspector.
Remember, aluminium welds are successfully applied every hour of every day. However, the metal is sensitive to heat and the surrounding atmosphere. It contracts quickly, so contraction cracking is a problem. Then there’s hydrogen porosity, an example of condensation contamination, to tackle. As long as the equipment current, application speed, and gas coverage are sufficient, the weld will probably form properly. A “probably” isn’t enough for a welding inspector, though, so the tools of that professional weld examiner’s trade are always within reach, as are the correct test procedures and a laser-focused mind.