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Improving microstructural and mechanical properties of dissimilar friction stir welded AZ61/AZ40 joint

Wang Liang, Wang Jixiang, Cui Chengwu, Zhou Peishan, Wang Bin, Zheng Hualin

Archives of Civil and Mechanical Engineering

2024

Vol. 24, no. 2

art. no. e66, 2024

This study focuses on the microstructure evolution and mechanical properties of dissimilar magnesium alloy friction stir welded AZ61/AZ40 joints achieved at different traverse speeds (50-130 mm/min) and a constant rotation speed (1200 rpm). The surfaces of the welds are relatively smooth without any obvious surface defects except for the FSW joint at a traverse speed of 50 mm/min. The nugget zone (NZ) is bowl-shaped due to the tapered probe. The Mg-based alloys were sufficiently mixed with each other in the NZ, and the interface was irregular. In addition, the NZ exhibits fine equiaxed grains due to dynamic recrystallization (DRX), and the grain size decreases with increasing traverse speed. The welded joints show a relatively discontinuous microhardness, and the lowest microhardness occurs in the thermo-mechanically affected zone (TMAZ) on the advancing side (AS). The strength increases as the traverse speed increases from 50 to 70 mm/min and then decreases as the traverse speed increases continually. An exceptionally high tensile strength of 235 MPa was achieved at a traverse speed of 70 mm/min. The combined effects of high-density dislocations and fine second phases (η-Al8Mn5 and β-Mg17Al12 phase) promote mechanical properties.

Friction Stir Welding of austenitic stainless steels

Meran C., Canyurt O. E.

Journal of Achievements in Materials and Manufacturing Engineering

2010

Vol. 43, nr 1

432--439

Purpose: Friction Stir Welding (FSW) was applied austenitic stainless steels that is difficult to weld using FSW technique. Proper weld can be obtained by using appropriate welding parameter. In this paper, the effect of different tool rotational speeds, traverse speeds, compressive tool forces, and tool angles was investigated. Design/methodology/approach: The dimension of 3 mm x 75 mm x 150 mm two stainless steel plates were used and butt welded by FSW method using 7.5 kW vertical head milling machine. All welded test specimens were prepared perpendicular to the weld line in order to determine the mechanical properties and tested with 12 MPa/sec stress rate under stress control using a servo-hydraulic Instron 8801. Microstructure of the welding zone and macrograph of the heat affected zone was investigated by SEM. Findings: The average grain size in the SZ was between 3 and 7 μm, which is smaller than that in the BM. The average grain size in the HAZ was about 20 μm, which is half of that in the BM. Fine-grained microstructures are present the welded area. The dark bands observed in the weld zone were also detected the microstructure of the transition zone. Dark and narrow bands do not consist of pores or cavities. It was determined that these bands do not process an ultra fine-grained microstructure. They are Cr2O3 oxide layers which over the surface of stainless steels may have been ruptured during friction stir welding and may form bands inside the welding bead due to stirring. Research limitations/implications: The proper cooling system helps to prevent the stirrer tool from the deformation. Practical implications: The strength of the welded zone of AISI 304 stainless steel can be easily found by implementing welding design parameters and high quality joints can be obtained. Originality/value: This study was performed in the frame of the TUBITAK project no 106M504, „Friction Stir Weldability of Stainless Steels and Investigation of the Affected Parameters on the Welding Quality”.