Seung Hwan C. Park

Effect of micro-texture on fracture location in friction stir weld of Mg alloy AZ61 during tensile test

Abstract Microstructural evolution of magnesium alloy AZ61 during friction stir welding and details of the relationship between the microstructure and mechanical properties are discussed. Tensile properties of the weld of Mg alloy AZ61 were strongly influenced by crystallographic orientation distribution as well as by grain size and dislocation density.

Microstructural evolution and its effect on Hall-Petch relationship in friction stir welding of thixomolded mg alloy AZ91D

Microstructural evolution of a thixomolded magnesium (Mg) alloy AZ91D during friction stir welding was investigated. Friction stir welding resulted in a homogeneous microstructure consisting of fine recrystallised α-Mg grains in the thixomolded material. The microstructural homogenisation and refinement was attributed to dynamic recrystallisation accompanied by the dissolution of the eutectic structure during the welding. The grain refinement in the stir zone was effective in increasing the hardness, as predicted by the Hall-Petch equation. The effect of grain size on hardness was smaller than that in conventional and rapidly solidified AZ91. This phenomenon may be explained as being due to the microstructure of the stir zone which consisted of fine equiaxed grains with a high density of dislocations.

Grain Structure Development During Friction Stir Welding of Single-Crystal Austenitic Stainless Steel

The high-resolution electron backscatter diffraction (EBSD) technique was used to study the grain boundary development and texture evolution during friction stir welding (FSW) in a single-crystal austenitic stainless steel. Strain-induced crystal rotations were found to be induced by simple shear deformation. With the crystal rotations, the single-crystal structure was broken up into a fine-grained polycrystalline aggregate in the stir zone. This process was deduced to be governed by continuous and discontinuous recrystallizations operating during the FSW process. The final texture which evolved in the stir zone was dominated by

Microstructures in Friction Stir Welded 304 Austenitic Stainless Steel

A/\bar{A}\left\{ {111} \right\} \, \langle 110 \rangle

Microstructure and Mechanical Properties of FSWed Aluminum Extrusion with Bobbin Tools

ideal simple shear orientations.

Corrosion Properties in Friction Stir Welded 304 Austenitic Stainless Steel

Friction stir welding (FSW) was applied to a 0.53% nitrogen stainless steel. The nitrogen content change and the microstructural evolution in the weld were investigated. The nitrogen content analysis revealed that the stir zone (SZ) showed roughly the same nitrogen content as the base material (BM). This result suggests that FSW is an effective welding process for keeping up nitrogen content of high-nitrogen steel weld. The microstructural observation showed that the weld had the BM, the SZ, the partially recrystallized zone (PRZ) and the heat affected zone (HAZ). The coarse grain structure of the BM changed to relatively fine microstructure of equiaxially recrystallized austenite grain structure in the SZ during FSW. The PRZ contained both the fine and coarse grain structures. The detailed TEM observations showed that the particles with about 11m in size were present in the advancing side of the SZ both along grain boundaries and grain interiors. The Cr nitride less than 100 nm was formed in the HAZ along grain boundaries, which indicates that a slight sensitization occurred in the HAZ during FSW.

Performance Enhancement of Co‐Based Alloy Tool for Friction Stir Welding of Ferritic Steel

Friction stir welding was applied to 304 austenitic stainless steel. The microstructural evolution and hardness distribution in the weld were investigated. The stir zone (SZ) and thermomechanically affected zone (TMAZ) showed dynamically recrystallised and recovered microstructures, respectively. The hardness of the SZ was higher than that of the base material and the maximum hardness was located in the TMAZ. The higher hardness in TMAZ was attributed to high density of dislocations and sub-grains. Electron microscopic observations revealed that ferrite and sigma phase were formed in austenite matrix in the SZ depending on the cooling rate during FSW.

Microstructural Evolution during Friction Stir Welding of Ultrafine Grained Al Alloys

Friction Stir Welding (FSW) has been applied to ultra fine grained (UFG) steel which is the plane carbon steel with the average grain size of 1mm. The plates of 5mm thickness was successfully welded using pcBN tool (polycrystalline cubic boron nitride) and the metallurgical and mechanical properties of the joint were evaluated. In the stir zone, Bainite has been formed which shows the highest harness in the joint. On the other hand, grain growth is observed in the heat affected zone. The joint effect of 88% has been obtained for UFG steel by FSW process.