The Effect of Welding Conditions on the Microstructure and Mechanical Properties of the Nugget Zone in AA7010 Alloy Friction Stir Welds

摘要

The effect of the welding conditions on the structure and properties of the nugget zone in Al-alloy 7010 friction stir welds (FSW) has been investigated. With low spindle speeds, for a given traverse speed, a temperature gradient exists between the top arid root of the weld, resulting in a significant variation in grain size, and hardness, such that the highest hardness occurs at the top surface. As the spindle speed is increased the temperature gradient is reduced and the microstructure and hardness becomes more homogeneous and the overall grain size increases. In contrast, the density of second phase particles reduces as the heat input rises, which leads to the tensile properties of the nugget zone initially improving with higher spindle speeds. However, at very high heat inputs the nugget properties start to deteriorate, due to precipitation during cooling, resulting in an optimum spindle speed that gives the best combination of nugget zone properties. As the traverse speed is increased it is necessary to increase the spindle speed to maintain the same energy density and this optimum condition.