The thermal cycle during dissimilar friction spot welding of Al alloy AA5754 to Mg alloy AZ31 was measured by thermocouples located at the welded region. The results revealed that the weld is exposed to a non-equilibrium solidus temperature induced by rapid heating and cooling. The microstructural analyses showed that the grain structure development in the stir zone was affected by grain boundary diffusion, interfacial diffusion, and dynamic recrystallization, which resulted in fine equiaxed grains of Al 12 Mg 17 in the weld center.Keywords: Friction spot welding; Peak temperature; Solidus temperature; Intermetallic compound; Diffusion.Friction spot welding (FSpW) or known also as refill friction stir spot welding is one of the friction stir welding (FSW) process variants capable of joining two or more materials in a spot-like lap joint configuration [1]. FSpW uses a nonconsumable tool consisting of three independent movable parts, including two rotating parts, the sleeve and the pin, and a stationary clamping ring. A schematic illustration of the process is shown in Fig. 1. The stationary clamping ring holds the materials against the baking bar, while the rotating sleeve plunges downward into the material, and the pin moves in the reverse direction. The rotating sleeve introduces plastic deformation and generates frictional heating, thereby plasticizing the materials.The sleeve squeezes the softening materials, filling the cavity left by the pin. Then,
In the present study, friction spot welding or refill friction stir spot welding was performed to consolidate dissimilar AA5754 Al and AZ31 Mg alloys. The intermetallic compounds of Al 12 Mg 17 and Al 3 Mg 2 were primarily found in the weld, distributed at the interface between the base materials and in the Al top sheet. The distribution of the intermetallic compounds and the interfacial area between the base materials affect the lap shear strength of the weld. It is concluded that the material flow induced by tool movement plays an important role in both the distribution of the intermetallic compounds and the interfacial area between the base materials.
In the present study, dissimilar welds of an Al-Mg-Mn alloy and a Zn-coated high-strength lowalloy steel were welded by refill friction stir spot welding. The maximum shear load recorded was approximately 7.8 kN, obtained from the weld produced with a 1600 rev min −1 tool rotational speed. Microstructural analyses showed the formation of a solid-liquid structure of an Al solid solution in Mg-Al-rich Zn liquid, which gives rise to the formation of Zn-rich Al region and microfissuring in some regions during welding. Exposure of steel surface to Mg-Al-rich Zn liquid led to the formation of Fe 2 Al 5 and Fe 4 Al 13 intermetallics. The presence of defective Zn-rich Al regions and Fe-Al intermetallics at the faying surface affects the weld strength.
In the present study, friction spot welding has been used for joining dissimilar AA5754 aluminum to AZ31 magnesium alloys. To get more insight into the microstructure, stop-action experimentation was employed. The welding cycle was forced to stop during the dwell time, and subsequently, the weld was quenched by pouring a mixed solution of ice and water to freeze the microstructure. Formation of the liquid phase leading to a formation of brittle intermetallic compound has been studied. Microstructural analyses reveal that formation of intercalated layers and a high density of grain boundaries induced by plastic deformation enhance the formation of eutectic structure during the welding process.
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