William H. Bingel

Effects of friction stir welding on microstructure of 7075 aluminum

Friction stir welding is a relatively new technique developed by The Welding Institute (TWI) for the joining of aluminum alloys. The technique, based on friction heating at the faying surfaces of two pieces to be joined, results in a joint created by interface deformation, heat, and solid-state diffusion. In evaluating friction stir welding, critical issues (beyond a sound joint) include microstructure control and localized mechanical property variations. A serious problem with fusion welding, even when a sound weld can be made, is the complete alteration of microstructure and the attendant loss of mechanical properties. Being a solid-state process, friction stir welding has the potential to avoid significant changes in microstructure and mechanical properties. The objective of this study was to evaluate the microstructural changes effected by friction stir welding of 7075 Al.

Fine-grain evolution in friction-stir processed 7050 aluminum

Abstract Evolution of the fine-grained structure in friction-stir processed aluminum has been studied using a rotating-tool plunge and extract technique. Initial sizes of newly recrystallized grains are on the order of 25–100 nm. These grains then grow to a size equivalent to that found in friction-stir processed aluminum, 2–5 μm, after heating 1–4 min at 350–450 °C.

Tensile and Fatigue Properties of Friction Stir Processed NiAl Bronze

Friction stir processing (FSP) produced local microstructural refinement in cast Ni Al Bronze. The refined microstructure quality was evaluated with mechanical property characterization using monotonic tension and fatigue testing as a function of FSP raster patterns. Modifying the cast NiAl bronze with FSP resulted in a 140 - 172 % increase in yield strength, and a 40 - 57% increase in tensile strength. Changing the raster pattern from a linear to a rectangular spiral raster increased the tensile elongations by 40 - 134%. This increase in elongation was attributed to increased microstructural uniformity through the depth of the FSP raster. The ability to transfer FSP technology was demonstrated with consistent tensile property data produced by three different laboratories. Fatigue characterization (both uniaxial and rotating-bending fatigue) showed that FSP improved the cast NiAl bronze fatigue resistance. Both types of fatigue testing showed differences in fatigue resistance as a function of processing parameters.

Friction stir processing of cast NiAl bronze

Friction stir processing (FSP) of cast NiAl bronze has resulted in significant increases in properties including more than doubling the yield greater that 40 percent increase in the threshold fatigue life; all achieved while increasing ductility. These and other strength, greater than a 60 percent increase in tensile strength, and property improvements were realized following studies of FSP procedures specifically for NiAl bronze. Within this manuscript, FSP procedures and other “lessons learned” are presented. Details of property improvements are documented elsewhere within this conference proceedings (see Fuller et al.). Presented herein are tool designs for efficient material flow, tool materials capable of long life at 1000°C, rastering procedures covering large surface areas, and other results pertinent to achieve improved properties in cast NiAl bronze following friction stir processing.

Feasibility of fabricating microwave waveguide using friction stir welding

Friction stir welding (FSW) as an alternative to brazing can be used for fabricating microwave waveguide structures. The FSW fabrication process is described, and the transmission and reflection of the straight sections of aluminum K-band waveguide made by FSW and brazing are compared. The section made by FSW exhibits 0.04dB lower transmission and slightly greater reflection than the brazed waveguide. In this preliminary evaluation, the welding process was not fully optimized. With optimization, FSW can provide a faster, more reliable fabrication process, but is limited to similar metals and cannot be used for fabricating window assemblies.