Friction stir weldability of a fine grained high tensile strength AZ31 magnesium alloy to an Al Mg alloy A5083 was evaluated by changing joining parameters, such as tool rotating speed, welding speed and insertion position of probe. A square butt dissimilar joint without any defect was obtained at the condition of welding speed 100 mm/min, tool rotating speed 500 rpm and offset 0 mm, by using a tool with shoulder diameter of 15 mm, pin diameter of 5 mm and pin length of 3.9 mm. Higher or lower welding speeds or rotating speeds led to the lack of bonding in the joint. Defects also occurred in the case that the offset was not 0 mm, i.e. the insertion position of the probe was shifted to either Mg side or Al side, even though the tool rotating speed was about 500 rpm and welding speed 100 mm/min. The maximum tensile strength of the dissimilar joints was about 115 MPa, lower than that of Al alloy base metal (about 308 MPa). Based on transmission electron microscopy, it can be suggested that the tensile strength of the dissimilar joint is mainly controlled by the thickness of IMC layer, which consists of Al 12 Mg 17 and Al 3 Mg 2 , and mechanical interlock between magnesium and aluminum alloys. Bond strength decreases remarkably when the mechanical interlock becomes weak due to the increase of the thickness of IMC layer.
High temperature arc plasma produced by employing Gas Tungsten Arc (GTA) is highly controllable, since it is stabilized with a shielding gas. Additionally, GTA requires low cost for equipment investment. Therefore, it is widely utilized as a heat source for material processing such as melting, cutting and welding, or decomposition and detoxification of toxic waste. Energy source properties of GTA strongly depend on the physical properties of the shielding gas. For instance, helium (He) gas or admixture of He gas with argon gas is employed as the shielding gas for conditions requiring high productivity in GTA welding process. Since He has low electrical conductivity especially in low temperature range due to high ionization potential, the current channel in He arc plasma is constricted near the arc axis. Consequently, the enhanced heat input intensity into a base material by the constriction increases weld depth and, thus, leads to the high productivity. However, the effect of the admixture on the heat input characteristics to the base metal is still not clear. In this paper, energy source properties of Ar-He GTA are predicted. The properties of arc plasma and the heat input intensity into a water-cooled copper anode are numerically analyzed.
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