Papers by Author: Tea Sung Jun

Abstract: The aim of the present work is to evaluate the possibility of using the Linear Friction Welding (LFW) technique to produce similar and dissimilar joints between a 2024 Al alloy and a 2124Al/25vol.%SiCP composite. In this solid state joining process the bonding of two flat edged components is achieved through frictional heating induced by their relative reciprocating motion, under an axial compressive force. Microstructural characterization of the welds was carried out by optical and scanning electron microscopy, to investigate the effect of LFW both on the aluminium alloy matrix and the reinforcement particles. The mechanical behaviour of the welded specimens was studied by means of hardness and tensile tests. The mechanisms of failure were investigated by SEM analyses of the fracture surfaces. LFW joints in MMCs resulted substantially defect free, with a uniform particle distribution, while a partial lack of bonding at the corners was observed in the others welds. The hardness decreased by approximately 10% in the welded zone, with some data fluctuations due to the complex microstructural modifications introduced by the LFW process. The joint efficiency, evaluated in respect to the UTS, was 90% for the Al alloy joints and 80% for the MMC joints. A decrease in the elongation to failure was measured in all the LFW specimens, probably related to the orientation of the plastic flow in the TMAZ, where the fracture generally occurred.

Abstract: In the present study, the process modelling of AMCs linear friction weldment was carried out. Four major stages of the process (Part 1: Warm-Up; Part 2: Osci-Forging; Part 3: Forging; Part 4: Cool-Down) were identified and simulated consecutively to generate the temperature field and residual strains distribution within the model. An eigenstrain model calibrated by the neutron diffraction results was also employed to capture the permanent deformation distribution. Good agreement between the process modelling and the experimental measurements was found.

Abstract: Linear friction welding (LFW) is a solid state joining process for bonding of two flatedged, complex geometry components through relative reciprocating motion under axial (compressive) forces. Although the proof of principle has been obtained some time ago, recently a number of studies have been published aimed at optimising the joining operations to obtain best joint strength and reduced distortion and residual stress. The present paper is devoted to the study of linear friction welds between components made from aluminium alloy 2124 matrix composite (AMC) reinforced with 25vol% particulate silicon carbide (SiCp). Neutron diffraction was used to measure interplanar lattice spacings in the matrix and reinforcement, and to deduce residual elastic strains and stresses as a function of distance from the bond line. Significant asymmetry is observed in the residual stress distribution within the two components being joined, that may be associated with the difference in the microstructure and texture.

Abstract: Friction welding processes, such as friction stir welding (FSW) and inertia friction welding (IFW) are popular candidate procedures for joining engineering materials (including dissimilar pairs) for advanced applications. The advantages of friction welding include lack of large scale material melting, ability to join dissimilar materials, and relatively low propensity to introduce defects into the weld joint. For these reasons FSW and IFW have become the subjects of a number of studies aimed at optimising the joining operations to obtain improved joint strength and reduce distortion and residual stress. In the present study we used the diffraction of high energy polychromatic synchrotron X-rays to measure interplanar lattice spacings and deduce nominal elastic strains in friction stir welds between dissimilar aluminium alloys AA5083 and AA6082, and in coupons from inertia friction welds between dissimilar nickel-base superalloys IN718 and RR1000. Energy-dispersive diffraction profiles were collected by two detectors mounted in the horizontal and vertical diffraction planes, providing information about lattice strains in two nearly perpendicular directions lying almost in the plane of the plate samples mounted perpendicularly to the incident beam. Two-dimensional maps of residual stresses in friction-welded joints were constructed. Apart from the 2D mapping technique, the sin2ψ method (transmission) was also used in the case of inertia friction-welded joint between nickel alloys. Comparison between the two results allowed the variation of the lattice parameter with the distance from the bond line to be deduced. It was found that friction welding of two dissimilar materials with significant strength mismatch may lead to the creation of a region of compressive stress in the vicinity of the bond line, in contrast with the behaviour observed for joints between similar materials.