Aluminum and its alloys are lightweight and strong. They are used a lot in modern transport, machine construction and structural work. From high-speed rail cars that meet EN 15085 to ships, parts for airplanes and special pressure vessels many important projects need welding of these metals.

Introduction:

Welding aluminum is different from welding carbon steel or stainless steel. A welder who is qualified under ISO 9606-1 to weld steels cannot weld aluminum structures. Why is that?

Aluminum has a thermal conductivity, a surface oxide that melts at a temperature three times higher than the metal itself and it tends to absorb hydrogen. This can cause porosity and solidification cracking. In addition the coefficient of expansion of aluminum is much higher than that of steel. Therefore a slower travel speed and more heat are needed to avoid burn-through.

Because of these differences welders must be qualified separately under ISO 9606-2:2004 which covers qualification testing of welders for fusion welding of aluminum and aluminum alloys. This standard sets important variables tests for welder performance and rules for acceptance that welders must meet when they weld aluminum and its alloys.

In this guide we discuss the requirements of ISO 9606-2:2004 the rules for qualification the important variables and the testing steps.

1. Why ISO 9606-1 Qualification Is Not Suitable for Aluminum Welding?

A common question companies ask when they start working with -ferrous metals is whether the same welders who were qualified under ISO 9606-1 for carbon or stainless steels can also weld aluminum alloys. The answer is simple: a welder qualified under ISO 9606-1 is not qualified to weld aluminum alloys under ISO 9606-2.

The reason comes from differences in the physical and metallurgical properties of steels and aluminum alloys. These differences include:

• thermal conductivity, up to five times greater than that of carbon steel.
• A high melting point of the surface oxide layer, Al2O3, which means thorough cleaning is needed before welding.
• A tendency to form porosity especially when shielding or backing gases contain hydrogen.

These are the reasons why a welder who is qualified to weld steel cannot weld aluminum unless they gain qualification under ISO 9606-2:2004.

2. Essential Variables & Range of Qualification Testing

ISO 9606-2:2004 says that welders are qualified for certain welding processes, product shapes, weld detail types, parent materials, consumables, weld sizes, welding positions and weld detail features. If a qualified welder works outside that range they must seek qualification.

A welder’s qualification is set by the variables listed in clause 5.1 of ISO 9606-2:2004. If a welder works outside the range of any of these variables they must pass more tests.

The basic welding variables that affect qualification include:

• a) welding process
• b) product form: plate or pipe
• c) weld detail type: butt weld or fillet weld
• d) parent material
• e) welding consumables
• f) weld size: material thickness and pipe’s outer diameter
• g) weld position
• h) weld detail features: backing, single or both sides, single or multiple layers

Welding Processes According to ISO 9606-2:2004

Fusion welding processes that can be used for aluminum welding are:

• 141 (TIG): Gas tungsten arc welding
• 131 (MIG): Metal inert gas welding
• 15: Plasma arc welding

Note for TIG welding: For process 141 changing the polarity from DC to AC or from AC to DC is considered a variable.

Pipes: Definitions:

The word plate includes plate and flat extruded bars while the word pipe covers tubes, extruded pipes and structural hollow sections.

Butt Welds and Fillet Welds:

A welder who is qualified for butt welds can weld all butt weld details and joints except branch connections.

Butt welds on plates also allow the welder to make butt welds, on pipes that have a diameter of 500 mm or more. If fillet welds are the type of production welding the welder must also pass tests for fillet welds.

Parent Materials: Scope of Qualification According to ISO 9606-2:2004

ISO 9606-2:2004 say that aluminum and aluminum alloys are split into the following groups, based on CR ISO 15608:

In my view when testing for qualification testing on Group 22 covers Groups 21 and 22. Testing on Group 23 covers Groups 21, 22 and 23. If dissimilar joints combine Groups 21‑23 with Group 24 or Group 25 I can test them by welding a test piece from Groups 21‑23 to Group 24 or Group 25.

3. Consumables, Gas Mixtures, Joint Detail Features

Aluminum Welding Consumables:

According to clause five point six of ISO 9606‑2:2004 a test that uses filler metal allows a weld that does not use filler metal for process one hundred forty one and process fifteen and the reverse is also true. However a weld that uses filler metal approved by a test with Al‑Mg alloy filler metal is not approved for a weld that uses Al‑Si alloy filler metal. The reverse is also true.

Shielding Gas Mixtures for MIG Welding (Process 131):

If the ratio of argon to helium in the shielding gas for process one hundred thirty one changes by than fifty percent this change is considered an essential variable.

Weld Layers:

According to clause four point three point three and clause five point eight, a weld that uses backing (mb) does not allow a weld that does not use backing (nb). However a single‑side weld (ss) is allowed to be used for a both‑side weld (bs). At the time a single‑layer weld (sl) does not allow a multi‑layer weld (ml).

4. Mandatory Inspection & Testing Visual Standards

All test pieces shall be. Tested, in the welder’s as‑welded condition by established procedures. If a weld was performed with backing the backing must be removed before testing.

Butt Weld (Plate or Pipe) Fillet Weld and Branch Connection:

• Visual Testing (VT) Mandatory – EN 970 / ISO 17637
• Radiographic Testing (RT) Mandatory (applies to all processes except process one hundred thirty one) – Not EN 1435 / ISO 17636
• Bend Testing Mandatory – Not applicable EN 910 / ISO 5173
• Fracture Testing Mandatory – EN 1320 / ISO 9018
• Special Requirements for Process 131 (MIG)

When a radiographic test is chosen for a weld that is made with process one hundred thirty one and the weld is a butt weld an extra test must be performed by a bend test or a fracture test. In particular two extra bend tests are required: one for the face and one for the root bend or two side bend tests; or two extra fracture tests are required: one for the face and one for the root fracture.

Macro Etching for MIG Test Pieces:

For butt welds that are made with process one hundred thirty one, a test – which is etched on only one side to show the weld details clearly – may be used instead of a fracture test if the test piece has already been radiographed. However least two cross‑sections must be examined.

Bend or Fracture Tests for Small Diameter Pipes:

For welded joints of pipes whose diameter’s twenty‑five millimetres or less a bend test or a fracture test may be replaced by a notch‑tensile test of the entire pipe.

5. Visual Inspection, Acceptance Criteria

Before any non‑destructive test the test piece must be inspected at first to remove all weld spray and to make sure that no grinding has been done on the root or face side of the weld except for a small finishing step that may be done by the welder if the examiner allows. The welder must also mark the start. Stop points of the root and cap passes.

Imperfection Acceptance Levels:

The quality of the weld is evaluated according to EN 30042 (ISO 10042). A welder passes the test if the weld imperfections match Quality level B. Weld metal, convexity, throat thickness and root penetration are tolerated up to Quality level C.

Bend Test Acceptance Criteria:

A bend‑test specimen must not show any single flaw or crack that is larger than three millimetres in any direction. Flaws and cracks on the edges of the specimen are not counted if they are caused by a lack of penetration a lack of fusion or by inclusions.

Bend Test Acceptance Criteria:

A bend‑test specimen must not show any flaw or crack that is larger than three millimetres in any direction. Flaws and cracks that are on the edges of the specimen are not counted if they are caused by a lack of penetration a lack of fusion or by inclusions.

Frequently Asked Questions (FAQs)

Related Blogs

1. Welder Certification (ISO 9606): Complete Guide to Testing, Certification and Qualification Range (2026)
2. ISO 9606-1 Welder Qualification Test: What Happens During the Certification Process?
3. Welder Certification Audit Checklist: What Inspectors Check Under ISO 9606-1
4. WPS Qualification Range: Key Variables Explained

Conclusion:

Qualifying welders under ISO 9606-2 is a step for any aluminum welding project. By knowing the qualification requirements, key variables and acceptance criteria fabricators can meet EN 15085 and other welding standards avoid the need for weld repair and improve weld quality.

First Welding Certification Pvt Ltd (pzvar.in) specialises in third‑party witnessing of welder tests, laboratory testing and WPS/WPQR development, for projects that meet ISO 9606-2 ISO 15614-2 and EN 15085.

Feel free to contact our IWE/EWE certified welding engineers and NDT specialists to discuss your welder qualification needs.