Temperature-dependent friction coefficient and its effect on modeling friction stir welding for aluminum alloys

Abstract

In friction stir welding (FSW), heat input and material flow characteristics are determined by the contact behavior between the tool and workpiece. Accordingly, calibrating the friction coefficient of the tool–workpiece interface is consequential to understand the joining process fully and achieve reasonable modeling. In the present study, the variation of friction coefficient with temperature between a steel tool and three aluminum alloys are obtained by experimental tests. As the temperature increases, the friction coefficient first slightly decreases, rapidly increases, and finally rapidly decreases until it approaches zero. The variation in friction coefficient during the three phases is further analyzed and explained using plowing and adhesive friction models based on examining the microscopic wear morphology and mechanism. A butt FSW test for AA5A06-H plates is also implemented. Subsequently, a fully coupled thermo–mechanical numerical model in which different friction coefficient schemes are used is developed based on the coupled Eulerian–Lagrangian method for simulating the FSW process. The results show that the numerical model considering the temperature-dependent friction coefficient can well reproduce the temperature field and material flow in the welding process.