Daniel,

there was an excellent AWS Welding Journal that time, containing lots of interesting information regarding the usage of FSW.

See:

http://www.aws.org/wj/2006/03/index.html

Perhaps you can find there somewhat of what you're looking for.

As well you can find a tremendous amount of information on a most current level by having a look into specific research-papers coming from the International Institute of Welding (IIW).

There the IIW Commission III (Resistance welding, solid state welding and allied joining processes) is specialized in the field of FSW.

Among others you can find the current papers:

No. III-1424-07 : Friction stir welding of aluminium high pressure die castings: parameter optimisation and gap bridgeability
No. III-1426-07 : Developments in NDT focusing defects in FSW of aluminium alloys
No. III-1429-07 : Cracking and local melting in Mg-alloy and Al-alloy during friction stir spot welding
No. III-1430-07 : Monitoring of the Friction Stir Welding process to describe parameter effects on joint quality
No. III-1431-07 : Friction stir welding of aluminium alloys of 2000 and 7000 series
No. III-1432-07 : Towards multidimensionality and flexibility in FSW using an industrial robot system
No. III-1433-07 : Aluminium Friction Stir Processing of AA 6061 Alloys
No. III-1434-07 : Aspects of the Material Flow during Friction Stir Welding of 5754 Al Alloy
No. III-1436-07 : Effects of welding conditions on microstructural transformations and mechanical properties in AE42HP friction welded joints
No. III-1418-07 : Friction stir welding - Aluminium - Part 1: Vocabulary
No. III-1419-07 : Friction stir welding - Aluminium - Part 2: Design of weld joints
No. III-1420-07 : Friction stir welding - Aluminium - Part 3: Qualification of welding operators
No. III-1421-07 : Friction stir welding - Aluminium - Part 4: Specification and qualification of welding

Hope this helps a bit...

Best regards,
Stephan