Friction stir technique played a vital role in recent industries as it has been utilized in welding and processing of metallic materials. Friction stir welding (FSW) is applied for joining the poorly weldable materials and enhancing the microstructure and the mechanical properties of the welded joints. Friction stir spot welding (FSSW), underwater friction stir welding (UFSW) and vertical compensation friction stir welding (VCFSW) are variants of FSW process. On the other hand, friction stir processing (FSP) is another method, whose basic principal originated from friction stirring technique, which can be utilized for manipulating the base materials by performing dynamic recrystallization on grains resulting in superior properties of the processed material. Friction stir alloying (FSA) is analogous to FSP with implanted reinforcement particles, producing surface composites. Like other fusion welding techniques, FSW process has its own defects which especially characterize the friction stir welded joints. Tunnels, voids, flash, lack of penetration, kissing bond and surface grooving are the common defects of FSW method. Since friction stirring action generates both thermal and mechanical loads beside the higher plastic deformation, finite element modeling (FEM) has been used in model and simulation this of the process. A few research gaps are pin pointed and some research recommendations are included.

Welding and processing of metallic materials by using friction stir technique: A review

The role of pin eccentricity in friction stir welding of Al-Mg-Si alloy sheets: microstructural evolution and mechanical properties

Mechanical and microstructural properties evolutions of various alloys welded through cooling assisted friction-stir welding: A review

Understanding process force transients with application towards defect detection during friction stir welding of aluminum alloys

Effects of tool shoulder size on the thermal process and material flow behaviors in ultrasonic vibration enhanced friction stir welding

Stir tools with different pin eccentricities were applied to the friction stir processing of Al-5052 alloy. Results show that pin eccentricity enhances material flow and refines grains of stir zone. The stir zone produced by a stir tool with 0.4 mm pin eccentricity performs the highest hardness and yield strength, attributing to the enhanced grain-boundary strengthening.

Influence of tool pin eccentricity on microstructural evolution and mechanical properties of friction stir processed Al-5052 alloy

Water cooling was applied during friction stir processing (FSP) of an Al-6061 alloy, and it was found that the strengthening efficiency induced by water cooling was varied, which was dependent on the initial base metal temper. As to the natural-aged Al-6061 alloy (6061-NA), the stir zone (SZ) was strengthened significantly by water cooling. Compared with the air-cooled FSP sample, the relatively high strength of the water-cooled FSP sample mainly arose from grain refinement, increased density of dislocations and large amounts of fine re-precipitated Guinier–Preston zones in the SZ. On the contrary, as to the annealed Al-6061 alloy (6061-O), the difference in the microstructural evolution between the FSP samples with and without water cooling was nonsignificant, where only finer grain morphology was observed in the water-cooled SZ, and thus the strengthening effects caused by water cooling became less.

Water Cooling Effects on the Microstructural Evolution and Mechanical Properties of Friction-Stir-Processed Al-6061 Alloy

Three different stir tools with the pin eccentricity of 0, 0.4 and 0.8 mm were applied to the friction stir processing (FSP) of Al-6061 alloy. Results show that the pin-affected zone (PAZ) enlarges and the grain size in the stir zone (SZ) decreases as the pin eccentricity increases. Moreover, the low peak FSP temperature induced by the pin eccentricity gives rise to the coarsening of strengthening precipitates in the SZ. Compared with the pin-eccentric FSP samples, the SZ produced without pin eccentricity exhibits the highest hardness and yield strength due to the high amount of fine precipitates. However, the application of pin eccentricity elevates the overall tensile properties of FSP samples through changing the failure location from heat-affected zone (HAZ) to SZ.

Zhaohui Ren

Papers

Influence of tool pin eccentricity on microstructural evolution and mechanical properties of friction stir processed Al-5052 alloy

Water Cooling Effects on the Microstructural Evolution and Mechanical Properties of Friction-Stir-Processed Al-6061 Alloy

Effect of Tool Pin Eccentricity on the Microstructure and Mechanical Properties of Friction Stir Processed Al-6061 Alloy