Friction stir butt welding between A6061 and S45C was achieved by plunging the tool into aluminum with slightly grinding the steel surface. The formation mechanism of weld interface was investigated by using straight and screw probes. Both of the probes created newly formed surface on the weld interface of steel surface and did not formed thick reaction layer not less than 1 mm on it. Also, the microstructure of aluminum along the weld interface within 3 mm from the weld surface was the similar in both probes. However, the surface morphology on weld interface of steel was di−erent in each probe. The surface morphology on weld interface for steel by screw probe exhibited a few wide linear scratched grooves along the welding direction, and aluminum was firmly adhered to the inside of these grooves. Thus, the screw probe increased the welding area and the weld strength by fabricating of the grooves. The groove formation is attributed to the built-up edge of steel on the screw probe and material flow around the probe.
In this study, joining mechanism of aluminum alloy/steel resistance spot-welding was investigated with micro observation and analysis on joining area by SEM-EDX,comparingwithsteel/steel and aluminum alloy/aluminum alloy spot joining. Results were obtained as follows. The shear tensile strength of aluminum alloy/steel resistance spot-welding was lower than a half of the maximum value of steel/steel due to the difference in resistance value between steel and aluminum alloy, close to the shear tensile strength of aluminum alloy/aluminum alloy. The aluminium alloy played a major role in joining of aluminum alloy/steel. In the resistance spot-welding of aluminum alloy/steel, the joining strength depended on aluminum melting at the joining interface and diffusing and adhering to steel. The intermetallics played the important role on the joining between steel and aluminum alloy. The fracture occurred on the aluminum side. On the aluminum alloy/steel resistance spot-welding, the hardness of steel increased by heating. On the other hand, the hardness of aluminum remained unchanged.
Aluminium welding processes are often used in marine and offshore industries especially for floating LNG (Liquefied Natural Gas) production, storage and LNG fuelled vessels. Welding deformations of aluminium plates are desired to reduce since it is larger than that of steel. Finite element models of MIG (Metal Inert Gas) welding and TIG (Tungsten Inert Gas) heating on aluminium plates by using the commercial finite element code Abaqus were developed in this study. A mixed material hardening model was employed in order to simulate aluminium material behaviours. A reduction method by in-process additional heating of plate bottom side was proposed and heating conditions were investigated by using the developed numerical models. Simulations and experiments of in-process additional heating of plate bottom side were carried out. The proposed method achieved a significant reduction of deformations for aluminium fillet welding.