Determination of microstructure and mechanical ;properties of AA7075/AA5182 weld connections jointed using TIG, MIG ve FSW methods

Aluminum and its alloys are the most commonly used building materials today because of their properties such as low densities, high strengths, good corrosion resistance and good weldability. Aluminium and its alloys can be joined with melting-based and pressure-based (solid phase) welding methods. TIG and MIG methods are the most preferred welding methods based on melting. However, due to the high temperature in melting-based welding methods, some metallurgical problems occur in the weld metal, which causes the mechanical properties to weaken in the welded joints. For this purpose, friction stir welding (FSW) has been found and developed by the British Welding Institute in the result of method research, which can be carried out without melting, for the weld of aluminium and its alloys. Thus, FSW method is also started to use for joining to the forehead of aluminium plates. This method offers many advantages over melting-based welding methods, and thanks to its successful applications, it finds usage area in the aerospace, space, marine, automotive, railway and armoured vehicles industries. In this study, AA7075 and AA5182 aluminium alloy plates in different specifications were joined by TIG, MIG and FSW methods. Different amperes (130, 140 and 150 A) values and two different weld groove (V and X) were used in joining with TIG and MIG. At the FSW, welds were made using different rotation speeds (980, 1325 and 1800 rpm), welding feed rate (108 and 233 mm/min) and stirred tips having two different geometries (conical helical and triangular). Microstructures of welded joints were investigated by an optical microscope and scanning electron microscope (SEM). Vickers hardness measurements were made in the weld zone of samples removed from each welded plate. Tensile and fatigue tests were also applied to the test specimens from welded plates. After the tensile test, the fracture surfaces and possible welding defects were analysed by SEM. In welded connections joined with the FSW method, it has been seen to contribute that the mechanical properties belonging to these welded joints better than the mechanical properties belonging to the TIG and MIG welded joints. Because the weld carried out at a temperature below the melting temperature of the aluminium alloys, and the microstructure had less porosity. The best mechanical properties were obtained from FSW method in a rotational speed of 980 rpm, a feed rate of 108 mm/min, and a stirrer tip having conical helical. These values are 264.7 MPa for tensile test and 158.8 MPa for fatigue test. The hardness value was very close to each other and varied depending on the rotation speed. The highest hardness was obtained as 87 HV at the connection at 1325-rpm rotation speed.