FINITE ELEMENT SIMULATION OF HEAT TRANSFER IN FRICTION STIR WELDING OF AL 7050

Friction welding is widely used in various industries. In friction welding, heat is generated by conversion of mechanical energy into thermal energy at the interface the work pieces during pin rotation under pressure. A three-dimensional thermo mechanical simulation of friction stir welding (FSW) processes is carried out for Aluminium Alloys of 6061and 7050 where the simulation results are compared directly with the measured temperature histories during FSW after process. The objective of the present work is to study and predict the heat transient generated in alloy aluminium plate welded by FSW method. A three dimensional model was developed by LS-Dyna software and heat cycles have been proposed during the welding of aluminium alloys 6061 and 7050. In this research, the simulations were carried out with linear velocity in the range of 140 to 225 mm/min and pin rotational speeds of 390 and 500 rpm. Increase in pin rotational speed, from 390 to 500 rpm, resulted in greater temperatures which translated to rise of recorded temperature of top and bottom of the specimens. This is in turn to a wider HAZ. In addition, it was observed that raising the linear velocity had an opposite effect. Finally, results of experimental and numerical data were correlated and validate

Influence of Parameters of Quenching and Partitioning Process on Microstructure and Fraction of Retained Austenite

Certain amount of retained austenite can increase ductility of steels because of the TRIP phenomenon during plastic deformation. One method for achieving this is partitioning of carbon into austenite to stabilize it at room temperature. The quenching and partitioning (Q&P) heat treatment leads to a microstructure consisting of martensite and stabilized retained austenite between martensite plates, which provides a better combination of strength and ductility. In this study, the effect of parameters of Q&P process (quenching temperature, partitioning temperature and partitioning time) on the microstructure and retained austenite volume fraction of a low alloy medium carbon steel was investigated. The results showed that the high increase in partitioning time causes the disappearance of martensite blades and reduction of austenite volume fraction. However, increasing of partitioning temperature made the retained austenite films become thicker and its volume fraction increase. On the other hand, by increasing the quenching temperature, carbon content of retained austenite increased sharply

The influence of Ni addition and hot-extrusion on the microstructure and tensile properties of Al-15%Mg<inf>2</inf>Si composite

The effects of nickel addition and hot-extrusion on the microstructure and tensile properties of in situ Al-15%Mg2Si composite specimens have been investigated. Al-15%Mg2Si composite ingots were prepared by an in situ process and different amounts of nickel (0.1, 0.3, 0.5, 1.0, 3.0 and 5.0wt% Ni) were added to the remelted composite. Optical microscopy (OM) and scanning electron microscopy (SEM) indicated that Ni addition changes the morphology of both primary and eutectic Mg2Si phases and decreases the size of primary Mg2Si particles from 42μm to 17μm. Hot-extrusion was found to be powerful in breaking the eutectic network and changing the size and morphology of pseudo-eutectic Mg2Si phase. The results obtained from tensile testing revealed that both Ni addition and hot-extrusion process improve ultimate tensile strength (UTS) and elongation values. Fracture surface examinations revealed a transition from brittle fracture mode in as-cast composite to ductile fracture in hot-extruded composite after Ni addition. This can be attributed to the changes in size and morphology of primary and eutectic Mg2Si phases and also the formation of more and finer α-Al phase. © 2012 Elsevier Ltd