Application of Hybrid Transient Thermal Tensioning/Trailing Active Cooling Treatment for Minimizing Distortion, Residual Stress, and Fatigue Crack Growth Rate of Friction Stir Welding Joints

n the present study, a hybrid in-process thermal treatment consisting of transient thermal tensioning (TTT) and trailing active cooling (TAC) has been applied to friction stir welding (FSW) of AA5083-H116 aluminum alloy plates with the main objective of improving fatigue crack growth performance of the weld joints. The TTT treatment was conducted during welding by placing two symmetrical secondary heat sources at both sides of the weldline ahead the tool at a heating temperature of 200°C combined with TAC treatment which employed quenching behind the tool. It was found that the hybrid TTT/TAC treatment showed excellent weld fatigue crack growth rate. In addition, the hybrid TTT/TAC treatment also showed better efficacy for minimizing distortion than single TTT or TAC treatment with the welding distortion reduction by the hybrid TTT/TAC treatment of 48.3 ±3.7% compared to as welded FSW joint. The beneficial effects of the hybrid TTT/TAC treatment seemed to be associated with temperature field modification which generated stronger thermal tensioning against compressive shrinkage stress in the weld region resulting in lower distortion and residual stress. This condition together with microstructural changes under hybrid TTT/TAC treatment could reduce fatigue crack growth rate of the FSW joints

Enhanced fatigue performance of tandem MIG 5083 aluminium alloy weld joints by heat sink and static thermal tensioning

In this work, tandem metal inert gas (MIG) welding using double torches with each torch contained a single wire feed was conducted to join AA5083 aluminium alloy plates. In order to minimise excessive welding distortion and residual stress and hence fatigue crack propagation rate due to high heat input, two methods for minimisation of welding distortion and residual stress, namely heat sink and static thermal tensioning (STT) treatments were applied during welding. The tandem MIG processes were conducted by locating two torches at a distance of 100 mm from each other with and without the treatments. Furthermore, welding distortion, residual stress, microstructure, hardness distribution, tensile strength and fatigue crack propagation were characterised and evaluated. Results showed that the use of heat sink effectively reduced fatigue crack propagation rate of the tandem weld, especially at low ΔK below 6 MPa√m. This fatigue crack propagation inhibition in the heat sink treated weld could be linked to its fine grained equiaxed structure and compressive residual stress. However, in term of welding distortion reduction, heat sink treatment seemed to be less effective compared to STT treatment. The beneficial effect of heat sink and STT in minimising welding distortion and residual stress was attributed to thermal tensioning due to temperature gradient and it is discussed in the present study

Tensile and fatigue properties of friction stir AZ31B-H24 magnesium alloy welded joints under the influences of pin geometry and tool rotation rate

Friction stir welding (FSW) is an innovative joining technology suitable for manufacture of magnesium welded lightweight structures. This paper presents tensile and fatigue crack growth rate (FCGR) behaviors of friction stir AZ31B-H24 magnesium alloy welded joints produced using two different pins, namely cylindrical and square pins at varying tool rotation rates of 910 rpm, 1500 rpm and 2280 rpm. Experiments conducted in this study included microstructural observations, Vickers microhardness measurements, tensile tests, residual stress measurements and FCGR tests. The results showed that increasing tool rotation rate increased ultimate tensile strength (UTS) of the welded joints and the highest values of UTS were achieved at 2280 rpm giving 229.0 MPa for the cylindrical pin and 200.3 MPa for the square pin. In the middle tension M(T) fatigue specimens, FCGR of FSW joint fabricated using the square pin at 2280 rpm was lower in comparison to the weld produced by the cylindrical pin. Subsequently, in single edge crack tension (SECT) specimens, the higher FCGRs were observed as the crack propagated across heat affected zone (HAZ) followed by the crack growth retardation in the weld nugget zone (WNZ). These fatigue crack growth rate behaviors were likely dictated by the weld microstructure and residual stresses

A new Jacobi spectral collocation method for solving 1+1 fractional Schrödinger equations and fractional coupled Schrödinger systems

The Jacobi spectral collocation method (JSCM) is constructed and used in combination with the operational matrix of fractional derivatives (described in the Caputo sense) for the numerical solution of the time-fractional Schrödinger equation (T-FSE) and the space-fractional Schrödinger equation (S-FSE). The main characteristic behind this approach is that it reduces such problems to those of solving a system of algebraic equations, which greatly simplifies the solution process. In addition, the presented approach is also applied to solve the time-fractional coupled Schrödinger system (T-FCSS). In order to demonstrate the validity and accuracy of the numerical scheme proposed, several numerical examples with their approximate solutions are presented with comparisons between our numerical results and those obtained by other methods