The Friction stir welding (FSW) is a complex process, depending on many factors: machine, clamping device, material and tools. Parameters that have a direct impact on the quality of the joint include the rotational speed, welding speed, clamping force, geometry and tool plunging depth. The paper presents the results of experimental studies concerning the effect of tool pin length on the microstructure and mechanical strength of joints of thin sheets made of Al 7075 alloy. A tool with an adjustable pin with concave shoulder was used to weld the joints. Different pin lengths were used, which were selected with respect to the thickness of the welded joint. The specimens were subjected to visual evaluation, metallographic tests and mechanical strength testing. The results indicate that the pin length has a decisive effect on the microstructural changes in the joint and thus influencing the strength of the FSW joints.

The aim of this paper was to present preliminary results of researches conducted in PZL Mielec within the FAST_FSW project (INNOLOT program) on the influence of tool eccentricity on microstructure and mechanical properties of 1.6 mm and 0.8 mm thick Al 7075 T6 sheets joints. Samples were performed using CNC milling machine. The range of tool eccentricity was 0-0.3 mm, rotational speed and feed rate were variable. The influence of the applied welding parameters on microstructure and mechanical properties of joints was assessed on the basis of metallographic inspections and tensile tests. Microstructural observations have shown that the change of FSW tool eccentricity affects the weld geometry: the mixing zone depth, the weld width, or the shape of the contact line.

Aluminum structures, and in particular an element of aerostructures, are strongly exposed to the effects of weather conditions. In the case of using new techniques of joining these structural elements, the selection of proper corrosion protection without losing the required properties of the joint may determine its potential application. This paper presents the results of experimental research concerning the influence of corrosion protection on the microstructure and mechanical strength of resistance spot welded (RSW) and refill friction stir spot welded (RFSSW) joints. The tests were carried out on 2024 T3 aluminum alloy, both sides alcladed. For comparison purposes, the following joints were welded: without any protection, with the primer layer, with anodic oxide coating, and with anodic oxide coating plus sealant between the overlapping surface of the welded metal sheet. The samples were visually inspected, and metallographic and mechanical strength examination was conducted. The test results indicate that the application of the protective layers and its type have an impact on the strength of RSW and RFSSW joints. The use of an adhesive or sealant in welded joints provides an increase in the load capacity of the joint.

Refill friction stir spot welding (RFSSW) is a new technique of metal structures joining. Within the framework of activities of PZL Mielec in R&D area (program Innolot) researches are realized which aim is to develop the RFSSW technology as a method of joining thin aluminum elements used in aircrafts constructions. The paper presents results of investigations on the RFSSW lap joints welded using rotations in the range from 1500 to 2000 rpm and tool sleeve plunge depth from 1.6 to 1.8 mm. Thin aluminum sheets of thickness 0.8 and 1.6 mm coated with alclad or anodized were welded. Results of the investigations prove that the most common cause of specimens breaking was presence of geometrical defect -the so called hook and weak bonding between parent material and working area of internal sleeve of RFSSW tool. The best tensile strength was reached in case of joint welded at rotational speed 2000 rpm and tool plunge depth 1.6 mm and 1.7 mm (5.37 kN and 5.87 kN adequately). These joints were characterized by very fine and uniform microstructure in the area between sleeve stirred zone and parent material.

One of the alternative method for welding method is a friction stir welding (FSW), which was developed in 1991 at TWI Ltd. (The Welding Institute) in the United Kingdom, initially especially for joining aluminum and its alloys [1]. This process consists in joining of materials in solid state, which eliminates the problems resulting from melting the material and its re-solidifying, such as, hot cracking, residual stresses and distortion created during conventional welding.

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