Avaliação dos ciclos térmicos de soldagem e sua influência nos defeitos, microestrutura e propriedades mecânicas de juntas de alumínio AA7075-T651 soldadas pelo processo FSW.

Abstract

Aluminum alloys are a great option for those who want low cost compared to other metals used in industry such as Titanium and Carbon Fiber Reinforced Polymer/Plastics, in addition to good mechanical properties, the 7XXX series aluminum alloys in turn stand out due to their excellent characteristics in relation to to other aluminum alloys, such as: its low density linked to good mechanical resistance, in addition to a relatively high hardness in relation to other aluminum alloys. However, when subjected to fusion joining techniques, this material does not have good weldability. One of the possible solutions to this bottleneck is to use solid state welding techniques, such as the FSW process, however, this process has several variables that influence the occurrence of welding defects, consequently, on the mechanical properties of these joints. This work aimed to measure the thermal cycles and correlate it with the mechanical properties and the occurrence of defects in 7075-T651 aluminum alloy joints welded by the FSW process, with the aim of evaluating the influence of the peak temperature and rate. of cooling on the quality of the joint depending on the welding parameters used. For mechanical characterization, uniaxial tensile tests, 60º root bending, analysis of macro and microstructures, Vickers hardness test and finally fractography were carried out. For joints with higher feed and rotation speeds (117 mm/min and 1585 RPM), a higher peak temperature (375,700 °C) and a higher cooling rate (7,745 °C/s) were found in relation to the others. joints 1 and 3 (47 mm/min and 470 RPM) which had lower values of peak temperature and cooling rate (358.735 °C and 3.226 °C/s, respectively), which led to the appearance of defects such as burr, finish coarse surface, lack of filling in the mixing zone and lower tensile strength. With these temperature analyzes it can be concluded that for this alloy lower speed parameters imply peak temperatures and lower cooling rates inducing a higher quality in the joints, higher temperatures induced greater defects in the joints.