FSW: AWS D17.3/D17.3M:2021

Insight into an American National Standard on FSW of Aluminium Alloys for Aerospace Applications Issued by the American Welding Society

 Headquarters of the American Welding Society in Doral, Florida,  8 km  (5 mi) west of Miami International Airport
Headquarters of the American Welding Society in Doral, Florida, 8 km (5 mi) west of Miami Airport, © Roquecorona, CC BY-SA 4.0

AWS D17.3 - D17.3M:2021 is
"An American National Standard" published by the American Welding Society (AWS) titled "Specification for Friction Stir Welding of Aluminium Alloys for Aerospace Applications."  


It includes the requirements for weldment design, qualification of personnel and procedures, fabrication, and inspection.


This informal insight provides just a general overview for educative purposes and gives some recommendations for further updates of this standard. The actual standard includes several drawings, additional details and specific requirements. For complete and accurate information, please refer to the AWS D17.3 - D17.3M_2021 standard itself, which can be obtained from the American Welding Society (AWS) and other sources at reasonable cost of USD $95 or less.[1][2]



This specification covers the general requirements for the friction stir welding (FSW) of aluminum alloys for aerospace applications.  The main content of this specification can be summarized as follows:

  1. Scope: Describes the purpose and applicability of the standard, outlining its coverage of the welding requirements for aluminum parts in the aerospace industry.
  2. Normative References: Lists the relevant documents referenced in the standard, which are necessary for its application.
  3. Definitions: Provides definitions of key terms used throughout the document to ensure clarity and consistency.
  4. General Requirements for FSW: Covers general guidelines for welding aluminum alloys for aerospace applications, including material requirements, joint design, weld preparations, welding processes, and quality control measures.
  5. Design of Weld Joints: Covers weldment design data and drawing information requirements.
  6. Welding Procedures: Outlines the requirements for developing and qualifying FSW procedures for aerospace applications. This section includes information on essential variables, welding procedure specifications (WPS) and welding procedure qualification records (WPQR).
  7. FSW Machine Operator Qualifications: Specifies the qualifications necessary for FSW machine operators involved in friction stir welding of aerospace parts. It includes information on performance qualification tests and certification requirements.
  8. Fabrication: Provides guidelines for the fabrication of aerospace components by FSW, covering various aspects such as welding equipment requirements, FSW tools, pre-weld joint preparatio and fit-up, tack welds, post-weld-finishing, weld identification requirements, acceptance inspection, rework and repair.
  9. Inspection and Testing: Details the requirements for inspection and testing of friction stir welds in aeroplanes and rockets. It includes information on visual inspection, non-destructive testing methods, destructive testing, and documentation of inspection and testing results.
  10. Annexes: Contains normative and supplementary information, such as guidance on joint design, preheat and post-weld heat treatment, weld repair, and acceptance criteria for various types of defects.   

Welding Details

Section 6.5 describes the preparation of a Welding Procedure Specification (WPS).


Minimum information to be listed in a WPS, according to AWS D17.3, Section 6.5 

Section Topic
6.5.1 Fabricator
  (1) Identification of the Fabricator
  (2) Number of WPQR
6.5.2 Base Metal
  (1) Product form such as sheet, plate, extrusion, casting, forging
  (2) Temper/Condition
  (3) Material specification (e.g. dimension and composition)
  (4) Surface coating
6.5.3 Base Metal Dimensions
  (1) Nominal thicknesses
  (2) Outside diameter of pipe or tube
6.5.4 Equipment
  (1) Model No
  (2) Serial No
  (3) Equipment manufacturer
6.5.5 FSW Tool 
  (1) Tool material, coatings and surface treatment
  (2) Engineering drawing or tool No
  (3) Nomilal probe length and tolerances
6.5.6 Tack Welding Procedure
6.5.7  Joint Design
  (1) Weld joint type
  (2) Sketch
  (3) Gap tolerances
  (4) Max. linear mismatch
  (5) Max angular mismatch
  (6) Start and stop area, exit hole, run-on and run-off tabs
6.5.8  Preweld Cleaning 
6.5.9  Weld Details 
  (1) Tool rotation (clockwise vs. counter-clockwise, tool rotation speed incl. ramp-up and ramp-down rotation speeds
  (2) Plunge rate
  (3) Weld run sequence and welding direction
  (4) Tilt angle
  (5) Side tilt angle
  (6) Dwell time
  (7) Nominal overlap length of lap joints
  (8) Advaning vs. retreating side of tool near the edge of upper sheet of lap joints
  (9) Force control, position control or temperature control
  (10) Nominal primary control parameter (force, depth or temperature)
  (11) Tool offset and direction
  (12) Number of passes
6.5.10 Travel speed
  (1) Ramp-up/ramp-down speed
  (2) Travel speed
6.5.11 Thermal management method
  (1) e.g. auxiliary heating or cooling of the FSW tool and/or workpiece
  (2) Pre-heat temperature, if applicable
  (3) Fixture or anvil design and material
6.5.12 Post-weld processing and heat treatment
  e.g. removal of flash, rectification of distortion, stress relieving or post-weld heat treatment
6.5.13 Welding method
  (1) Conventional FSW

(2) Retractable probe

  (3) Self reacting FSW (Bobbin tool)
  (4) SSFSW (stationary shoulder FSW)

Essential Variables

The "Essential Variable Ranges" of friction stir welding according to AWS D17.3, Table 6.5

Variable Conventional FSW Retractable Probe Stationary Shoulder Self-reacting



 ± 5%  ± 5% ± 5% ± 5%
Plunge Depth   ± 5%  ± 5% ± 5% ± 5%
Primary Control Parameter   ± 5%  ± 5% ± 5% ± 5%
Plunge Rate   ± 5%  ± 5% ± 5% ± 5%
Travel Speed   ± 5%  ± 5% ± 5% ± 5%
Tilt Angle   ± 0.5°  ± 0.5° ± 0.5° ± 0.5°
Side Tilt Angle   ± 0.5°  ± 0.5° ± 0.5° ± 0.5°
Dwell Time   ± 5%  ± 5% ± 5% ± 5%

Classification and Acceptance Criteria

Classification: All welds produced in accordance with Section 4 of AWS D17.3/D17.3M:2001 have to be classified within three Classes based on the function and the use of the friction stir welded joint:


  • Class A — Critical Application: A friction stir welded joint, whose failure would cause significant danger to personnel, loss of the flight vehicle, loss of control, loss of a  flight hardware system or the flight software, loss of a major component, unintentional release of critical solids, fluids or gases, inability to release armament stores, abortion of the mission, or an operating penalty.
  • Class B — Semicritical Application: A welded joint whose failure would reduce the overall performance of a  flight hardware system or the flight software or preclude the intended functioning or use of equipment, but loss of the flight hardware system or flight software, endangerment of personnel would not occur.
  • Class C — Noncritical Application: A welded joint whose failure would not affect the efficiency of the system or endanger personnel. 


The choice of the Class shall consider the material and process aspects that affect the flightworthiness, and take into account the design requirements, subsequent processing (e.g. coating or painting), type of stresses (e.g. static or dynamic loads), service conditions (e.g. temperature and corrosion during service) and the consequences of failure.


According to Section 9.4 and Table 9.1 of the standard the following Acceptance Criteria have to be defined for these classes:


The "Acceptace Criteria" of friction stir welding according to AWS D17.3, Table 6.5


Class A —



Class B —



Class C —



Cracks None None None
Incomplete joint penetration in full penetration welds None None None
Subsurface inlusions and/or cavities      
(a) Individual size (maximum)

0.33 T or 1.5 mm (0.06 in) whichever is less

0.5 T or 2.3 mm (0.09 in) whichever is less Not applicable
(b) Spacing (minimum) Four times the size of the larger adjacent discontinuity Two times the size of the larger adjacent discontinuity Not applicable
(c) Accumulated length in any 76 mm (3 in) of weld (maximum) 1.33 T or 6.1 mm (0.24 in) whichever is less 1.33 T or 6.1 mm (0.24 in) whichever is less 1.33 T or 6.1 mm (0.24 in) whichever is less
Cavity open to the surface None None None
Linear mismatch across joint (maximum) 0.05 T 0.075 T Not applicable
Angular distortion (degrees, maximum) Not applicable
Underfill (maximum) if the face will not be post-weld machined      
(a) For the full length of the weld (max. depth)  0.05 T 0.075 T  0.1 T
(b) Individual defect (max. depth) 0.07 T or
0.76 mm (0.03 in) whichever is less
0.1 T or
0.76 mm (0.03 in) whichever is less
0.125 T or
0.76 mm (0.03 in) whichever is less
(c) Accumulaed length in any 76 mm (3 in) of weld (maximum)  5.1 mm (0.2 in) 15 mm (0.6 in) 25 mm (1 in)

Welding Procedure Specification (WPS)

An example of a form of a Welding Procedure Specification (WPS) is show in the Annex B of the standard just for information.


Example of a Welding Procedure Specification (WPS) for Friction Stir Welding

Qualified supporting WPQR(s):               WPS No:
Governing code: AWS D17.3 Date:
FSW method: Engineer:
Background Sketch of Joint Design
Weld Class:  
Aluminium Alloys  



Thickness range




Thickness range

Grain direction:  

Pre-weld cleaning:

Root-face or surface coating  
Set-up Friction Stir Welding Variables
FSW machine model: Axial force, kN (lbs)
Serial No: Spindle speed (rpm) 
FSW tool No.  Direction of tool rotation: 
FSW joint type  Tilt angle (°):
Joint gap, mm (in): Plunge speed, mm/min (in/min) 
Tool offset, mm (in):  Dwell time (s): 
FSW fixture drawing No:  Clamp pressure, kPa (psi): 
Anvil material:  Travel speed, mm/min (in/min): 

Welding Engineer:



Signature and date




Signature and date

Review by NASA

It is NASA's policy to use "voluntary consensus standards", whereever possible. The subsequently superseded version of AWS D17.3/D17.3M (2016) has been reviewed and approved for use by NASA.[3][4] The NASA standard NASA-STD-6016C, which has been approved for public release and unlimited distribution on 30 June 2021, requests that aluminum alloys for spaceflight hardware that provides mission-critical functions shall meet the requirements.


Recommendations for Further Updates

The standard is well-worded and easy to understand. However, the following aspects should be considered for further updates:


According to the standard, "the FSW machine operator shall have vision acuity 20/30 or better in either eye and shall be able to read the Jaeger No. 2 Eye Chart" at a distance of 4 m (16 in) using corrected or uncorrected vision. The use of a non-standardised  Jaeger card in a standard is not reliable, because the variability of the actual size of test letters on different Jaeger cards currently in use is very high.[5]  Exceptions to this Vision Test should be permitted, e.g. if the FSW machine is equipped with cameras and/or other sensors. Employers must be eanabled to consider individually, whether any reasonable accommodations could be made to assist a visually impaired employee with their job. Examples of reasonable accommodations include magnifiers on computer screens.


Please explain the terminology "groove welds only" in Table 9.1 or delete this. Section 5.1.1. mentions only square-groove welds.


The "third body" that is mentioned in the foreword, is not identical to the welding tool, but to the plasticised material that surrounds the rotating tool.


The standard requests that the tilt angle should be maintained by ± 0.5°. This might be reasonble when using a tilt angle of 2° ± 0.5° , but if you use zero tilt tools, the tilt angle should normally not vary from - 0.5° to + 0.5°, if you use a rigid machine or if you apply deflection mapping


See also


  1. AWS D17.3 - D17.3M_2021: "Specification for Friction Stir Welding of Aluminium Alloys for Aerospace Applications."  ISBN Print: 978-1-64322-151-9, ISBN PDF: 978-1-64322-152-6 (AWS web site).

  2. The complete standard will be displayed by opening the following link in Google Chrome: AWS D17.3 - D17.3M_2021 but it can only be partially printed (uploaded by Leonardo Rincon, 10 Sep 2021).
  3. Full text and a pdf version of the superseded 2016 issue of AWS D17.3/D17.3M:2016.
  4. Standard Materials and Processes Requirements for Spacecraft. NASA-STD-6016C, approved on 30 June 2021.
  5. A. Colenbrander and P. Runge: Can Jaeger Numbers Be Standardized? ARVO Annual Meeting Abstract, May 2007.