Welding and brazing: choose a qualified joining route

Distinguish the processes

Fusion welding melts the parent material locally. Brazing joins using a molten filler while the parent parts remain solid; TWI explains that joint compatibility and the gap are central to successful brazing. These are different route choices, so a weld procedure cannot simply be reused as a brazing instruction for the same drawing.

Strength changes near a weld

TWI identifies local softening mechanisms in both work-hardened and heat-treatable aluminium alloys. It also explains why some higher-strength alloys are difficult to fusion weld and why filler selection must consider cracking, properties and corrosion. A base-metal tensile value is therefore insufficient evidence for the capacity of the completed joint.

Specify the completed assembly

Identify the actual parent alloys and tempers, joint geometry and performance requirements. Ask the joining specialist to propose the process, filler and inspection basis. Include cosmetic anodized surfaces where applicable, because filler choice can affect finishing appearance. Seek qualification evidence for the actual combination rather than accepting an unqualified claim that an alloy family is weldable.

Verification is application-specific

Establish the governing joining specification, procedure approval, operator requirements and acceptance tests before production. For brazed assemblies, request confirmation of filler compatibility, atmosphere or flux route and post-process cleaning requirements. For either route, agree dimensions and properties in the finished state. This introduction intentionally excludes filler-selection tables, joining settings and guarantees about recovery of parent-metal strength.

Sources and verification

Selected facts checked 14 October 2026. Source data is reference information, not certification of supplied material.

• TWI • Weldability of aluminium alloys — Job Knowledge 21; public page · checked 2026-10-14
• TWI • What is brazing? — Live public page; no publication revision stated · checked 2026-10-14

Choose controls for the joining mechanism

TWI identifies moisture and contamination paths for fusion-weld porosity. UACJ treats brazing as a layered material system. European Aluminium separately addresses adhesive surface preparation and the rivet/die/material stack for mechanical joining. The process-specific controls differ: select the mechanism, surfaces and joint access before defining trials and finished-joint inspection.

Source: www.twi-global.com, www.uacj.co.jp, european-aluminium.eu, european-aluminium.eu