ISO 25239:2020(en)

A Sneak Preview of the new Standard on Friction Stir Welding

Friction stir welding of Aluminium according to ISO 25239:2020(en)

Courtesy of TWI Ltd


Many companies supported the development, review and update of ISO 25239 on friction stir welding of aluminium and have actively participated in Commission C-III-B-WGB1 of IIW, which has circulated drafts of ISO/DIS 25239-1 to -5 to all IIW-Members in May 2019. This is the first revision to this standard since it was first issued in 2010.


The new standard has been published in June 2020. The electronic and printed versions are available for sale on the ISO-Website



Low Cost Printed Versions

Low cost print-outs of the English Version of ISO 25239 are available from the Czech Republic:


ISO-Standard Price (EUR) Price (USD)
ČSN EN ISO 25239-1:2020 (E) (1 Feb. 2021), English Version 12,50 €  13.30 $
ČSN EN ISO 25239-2:2020 (E) (1 Feb. 2021), English Version 8,20 €  8.80 $
ČSN EN ISO 25239-3:2020 (E) (1 Feb. 2021), English Version 12,50 €  13.30 $
ČSN EN ISO 25239-4:2020 (E) (1 Feb. 2021), English Version 12,90 €  13.80 $
ČSN EN ISO 25239-5:2020 (E) (1 Feb. 2021), English Version 12,50 €  13.30 $
GLS Courier Service (Postage) 9,90 €  13.30 $
Total: 68,20 € 75,80 $


AluStir ordered the complete package during a weekend. They despatched the package on Monday at 7:25 and provided a tracking number. It was collected by GLS in the Czech Republic on Monday at 7:40 and delivered at AluStir on Thursday at 11:32. The printouts were wrapped in cling film and packed in a cardboard envelope.


Free-of-Charge Previews

Previews of ISO 25239-1:2020(en) are currently available free of charge via the links shown in the following sections:



ISO 25239-1:2020(en) — Part 1: Vocabulary

Part 1 gives defines the terminology that should be used in friction stir welding, sorted by alphabet. It covers everything from “adjustable tool probe” to “welding procedure specification (WPS)”


Eleven annotated figures show for instance:

  • The “Basic principle of friction stir welding” (Fig. 2)
  • The “Bobbin tool” (Fig. 3)
  • The “Side tilt angle, heel, heel plunge depth, and tilt angle” (Fig. 6)
  • A non-typical “Cross-section of friction stir lap weld showing a hook”, while using non-optimised tools (Fig. 7)
  • A non-optimised “Cross-section showing example of root flaws in full thickness butt weld” when using a probe that is too short in relation to the sheet thickness (Fig. 8),
  • The “Lateral offset showing the centreline of the tool not centred on the joint” caused by inaccurate set-up or a faulty seam tracker (Fig. 9),
  • An “Example of a friction stir welding tool” with a very basic profile of a flat shoulder, a threaded probe with a spherical cap, as used in the first welding experiments in 1991
  • The “Toe flash” caused by excessive metal protruding above the weld face (Fig 11)

A complete version of Part 1 including the figures is available free of charge at:   

ISO 25239-1:2020(en) — Part 2: Design of weld joints

Part 2 covers the “Design requirements”, subdivided into “Documentation”, “Joint design” and “Additional information.”


A limited preview version showing the table of content of this part is available at
ISO 25239-1:2020(en) — FSW — Al — Part 2: Design of weld joints.


ISO 25239-1:2020(en)  — Part 3: Qualification of welding operators

Part 3 describes the “Qualification of welding operators” which is more complicated than that of a milling machine operator.


The standard describes the “Requirements” and the “Certificate.” It focuses on “Welding operator qualification,” “Essential variables and ranges of qualification,” “Qualification methods,” “Test welds” and the “Test report.”


“Annex A Knowledge of the welding unit and its operation” and “Annex B Knowledge of welding technology” as well as “Annex C Example of a qualification test certificate for FSW welding operators” are attached to this part of the standard



A limited preview version showing the table of content of this part is available at
ISO 25239-1:2020(en) — FSW — Al — Part  3: Qualification of welding operators.



ISO 25239-1:2020(en) — Part 4: Specification and qualification of welding procedures

Part 4 describes the “Development and qualification of welding procedures” and defines the “Technical content of a pWPS”, i.e. a preliminary welding procedure. The “Annex A Example of a form for preliminary welding procedure specification (pWPS) and welding procedure specification (WPS)” and “Annex D Example welding procedure qualification record form (WPQR)“ are particularly useful, if a company doesn’t want to disclose the details of the tool design and welding parameters used. This part contains also “Annex B Non-destructive testing” and “Annex C Hammer S-bend test of lap welds.”


For the “Qualification based on a welding procedure test” or for the “Qualification based on pre-production welding test” the standard covers, for instance, the following aspects:

  • Test pieces
  • Examination and testing of test pieces
  • Range of qualification
  • Welding procedure qualification record

A limited preview version showing the table of content of this part is available at
ISO 25239-1:2020(en) — FSW — Al — Part  4: Specification and qualification of welding procedures.



ISO 25239-1:2020(en) — Part 5: Quality and inspection requirements

This is arguably the most important part of the standard and it is regularly used when contracts are issued to machine manufacturers and job shops. It describes the “Quality requirements“ in twelve sections:


This part of the standard describes the requirements regarding “Welding personnel”, “Inspection and testing personnel”, “Equipment” and “FSW tools.”


A written “Welding procedure specification” has to be issued, which covers for instance the “Pre-weld joint preparation and fit-up”, the “Preheating and interpass temperature control”, the procedure for “Tack welds” if they are used, “Welding” and “Postweld heat treatment.”


As in other welding processes, the needs for “Inspection and testing” and “Identification and traceability.”


The most useful table is shown in Annex A and summarises “Imperfections, testing and examination, acceptance levels and ISO 6520-1 reference numbers.” To understand the content of this table is the key for success for assessing and improving the weld quality – and if something goes wrong, it contains undisputed information on flaws that may be accepted and defects that must be rejected.


A limited preview version showing the table of content of this part is available at
ISO 25239-1:2020(en) — FSW — Al — Part  5: Quality and inspection requirements.