The team also performed a series of mechanical tests on friction-stir-welded aluminum alloys. To stabilize the welded material, the test samples first underwent a postweld heat treatment (120°C for 24 hrs to create an as-welded [as-FSW] +T6 temper). As expected of any weldment, tensile specimens loaded transverse to the weld direction exhibited a slight reduction in strength level and an elongation in the as-FSW condition and also revealed that the fracture occurred in the HAZ.

AFRL researchers are expanding the knowledge of microstructure-property relationships, corrosion and failure modes, and life-cycle benefits in friction-stir-welded materials. They are also developing databases and process specifications so that manufacturers employing these FSW tools can consistently achieve desirable and predictable properties, enabling FSW to be qualified for use in the manufacture of major structural assemblies such as reusable cryotank applications for space.

Besides the AFRL activity, automotive, aerospace, and shipbuilding companies are also vigorously pursuing FSW technology to join not only aluminum alloys but also steels and, more recently, titanium alloys. Research is rapidly progressing in such areas as novel tool design, process parameter optimization, and FSW process modeling. As a result of these advances, FSW could soon produce joints with mechanical properties better than fusion-welded or mechanically fastened joints and provide cost-effective methods for repairing defects in metal surfaces.

Dr. Kumar V. Jata, Dr. Lee Semiatin, Dr. Reji John, and Dr. Peter S. Meltzer (General Dynamics), of the Air Force Research Laboratory’s Materials and Manufacturing Directorate, wrote this article. For more information visit http://www.afrl.af.mil/techconn_index.asp. Reference document ML-H-06-01.