Yaxin Xu

Effect of welding speed on microstructures and mechanical properties of Al/Cu bimetal composite tubes by a novel friction-based welding process

In this work, a novel friction-based welding technology was developed to weld Al/Cu bimetallic tubes. The macrostructure, microstructure evolutions, and mechanical properties of the joint under different welding speeds were investigated. Void defects are observed on the joint interface, especially at the welding speed 60xa0mm/min. From the Al side to the Cu side, the reaction layer can be divided into five layers. In addition, welding speed has an important influence on the microstructure evolution of reaction layer. Compression-shear testing results show that the shear strength decreases with the increase of the welding speed. The failure of compression-shear samples is first generated at the junction of hypereutectic layer and intermetallic compound (IMC) layer, and then, the crack propagates along the interface of the hypereutectic layer and IMC layer or through the hypereutectic layer to the eutectic layer.

Numerical modelling and experimental investigation of thermal and material flow in probeless friction stir spot welding process of Al 2198-T8

ABSTRACT A finite element model based on software Abaqus/Explicit and experimentation was established to describe the probeless friction stir spot welding process of 2198-T8 aluminium alloy. An Arbitrary Lagrangian–Eulerian method was adopted in this model in which the Johnson–Cook equation was used to describe the flow stress depending on temperature, plastic strain and strain rate. The experimental results revealed the representative microstructure of the joint which has three typical zones: stir zone, thermo mechanically affected zone and heat affected zone. The relationship between the temperature field and dwell time was investigated based on the accurate description of temperature field. A model of the material flow was developed based on the numerical and experimental results.