Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.

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Friction Stir Welding and Processing

Recent advances in friction-stir welding : Process, weldment structure and properties

A review of dynamic recrystallization phenomena in metallic materials

A review on selective laser sintering/melting (SLS/SLM) of aluminium alloy powders: Processing, microstructure, and properties

http://nanomechanics.mit.edu/sites/default/files/documents/2007_Acta_nc_Overview.143.pdf

Toward a quantitative understanding of mechanical behavior of nanocrystalline metals

https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=7617&context=etd

Microstructural evaluation of hydrogen embrittlement and successive recovery in advanced high strength steel

Friction Stir Welding of Steel T-joint Configurations

High base metal dilution (50 pct) dissimilar metal weld between A508 low-alloy steel and 309L clad layer was fabricated to investigate the effect of extended post-weld heat treatment (PWHT) on microstructure and mechanical properties. Extended PWHT at 607 °C caused significant carbon migration and microstructural change across the fusion boundary. Following PWHT at 607 °C for 20 hours, the carbon-enriched zone exhibited little to no reduction in hardness although 20 pct hardness reduction occurred in the remainder of the first butter layer. This is because tempering of the martensite in the carbon-enriched zone was entirely offset by the formation of a high density of chromium carbides. In contrast, following PWHT at 607 °C for 20 hours the average hardness of the carbon-depleted zone decreased from 241 HV to 169 HV due to the elimination of martensite, ferrite grain coarsening and carbon depletion. In addition, the extended PWHT significantly enhanced the mismatch in mechanical properties between the carbon-enriched zone (351 HV) and the adjacent carbon-depleted zone (169 HV). The formation of chromium carbides (less than 200 nm in size) in the carbon-enriched zone reduced the carbon concentration in the matrix, generating a continued driving force for carbon migration from A508 steel to the weld metal during PWHT.

Tracy W. Nelson

Papers

Microstructural evaluation of hydrogen embrittlement and successive recovery in advanced high strength steel

Friction Stir Welding of Steel T-joint Configurations

Effect of Post-weld Heat Treatment on Microstructure and Mechanical Properties of Dissimilar Metal Weld Used in Power Plants

Crystallographic Reconstruction of Parent Austenite Twin Boundaries in a Lath Martensitic Steel

Tool Geometries And Process Parameters Required to Friction Stir Weld High Melting Temperature Materials