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In the present study, tensile behavior of friction-stir-welded AZ31 (Mg-3.6Al-1Zn-0.6Mn in wt pct)-H24 Mg alloy was investigated. It was found that the tensile property, particularly tensile elongation, of AZ31-H24 alloy was significantly degraded with friction stir welding (FSW). The tensile fracture always occurred at the boundary between the thermomechanically affected zone (TMAZ) and the stir zone (SZ) on the advancing side. The fractographic examination on the tensile-fractured AZ31-H24 alloy specimen showed a mixed mode of cleavage and dimpled rupture. The AES analysis suggested that the significant reduction in tensile elongation of friction-stir-welded AZ31-H24 Mg alloy was attributable to the entrapped oxides along the boundary between the TMAZ and SZ.Since the development of the friction stir welding (FSW) process in 1991 by The Welding Institute (TWI) in the United Kingdom, this joining method has gathered a great amount of interest in a variety of applications, particularly in aerospace and automotive industries. [1,2,3] The advantages of this solid-state joining process encompass better mechanical properties, low residual stress and deformation, weight savings, and reduced occurrence of defects compared to conventional welding methods. [4] At present, research on the FSW process has mainly focused on the joining of Al alloys, [5,6,7] and the FSW of Al alloy is now in the early stage of commercial usage. Magnesium alloys are the lightest structural alloys commercially available, and the interest in friction stir welding of Mg alloys is rapidly increasing. [8] However, the tensile ductility of Mg alloys has been reported to be greatly reduced with FSW compared to that of Al alloys, and the degrading mechanism has not been completely established. [9] The objective of the present study was therefore to examine the tensile behavior of friction-stir-welded AZ31-H24 Mg alloy. The mechanism for the deterioration of tensile property was proposed based on the Auger electron spectroscopy (AES) data and the microstructural observations documented by optical microscope and scanning electron microscope (SEM).The 4-mm-thick AZ31(Mg-3.6Al-1Zn-0.6Mn in wt pct)-H24 Mg alloy plate was used in the present study. Friction stir welding was conducted at varying rotating speeds of 1200, 1400, and 1600 rpm and welding speeds of 0.1 and 0.2 mpm (m/min). Tensile specimens were prepared with the tensile direction perpendicular to the welding direction, so that the weld zone is located in the middle of the specimen. Tensile tests were performed at a nominal strain rate of 1 ϫ 10 Ϫ3 /s on an S2 model R&B (Daejeon, Korea) universal testing machine. The side and fracture surfaces of tested specimens were examined using a scanning electron microscope (SEM). The Mg alloys are known to have a relatively thick oxide layer on the surface, and these oxides could be entrapped into the weld zone during the friction-stir-welded process. Since these oxides in the weld zone would affect the tensile property of friction-stir-welded AZ31-H24, A...

In the present study, tensile behavior of friction-stir-welded Al 6061-T651 with varying welding parameters, including rotating and welding speeds, was examined. The 4-mm-thick Al 6061-T651 alloy plates were FSW with varying tool rotating speeds, 1000, 1400, 1600, 2000, and 2500 rpm, and welding speeds, 0.1, 0.2, 0.3, to 0.4 mpm (m/min). Tensile specimens were prepared with the tensile direction perpendicular to the welding direction, so that the weld zone is located in the middle of the specimen. It was found that the tensile elongation of friction-stir-welded Al 6061-T651 decreased with decreasing welding speed or increasing rotating speed. The yield and ultimate tensile strength were also affected, but to a significantly lesser degree, with varying welding parameters. The micrographic and fractographic observations strongly suggested that the change in tensile behavior of friction-stir-welded Al 6061-T651 was largely related to the clustering of coarse Mg 2 Si precipitates, due to the whirling and hurling action by severe plastic flow in the weld zone. Low welding speed or high rotating speed tended to encourage the plastic flow per unit time and consequently the clustering of coarse precipitates.

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