Influence of Welding Parameters on the Mechanical Properties and Microstructure of 7075-T651 Aluminum Alloys Welded Joints Performed by FSW Process

Abstract

Aluminum alloys of 7xxx series have excellent characteristics and mechanical properties, being widely used in primary aircraft structures. However, the welding of these alloys by conventional arc welding processes results in an excessive mechanical resistance degradation and increasing in residual stress level. In this context, Friction Stir Welding (FSW) process has received attention in recent years mainly because it does not reach the materials melting point during the process. This work aims to evaluate the influence of the tool rotation and welding speed on microstructure and mechanical properties of AA 7075-T651 aluminum alloy welded joints by FSW process. Therefore, four welded joints obtained with different welding and tool rotation speed were subjected to tensile and microhardness tests. The microstructures of the welded joints were evaluated through analysis by optical microscopy and Scanning Electron Microscopy (SEM). The retreating side of the welded joints showed a higher occurrence of microstructural welding defects. Welded joints with yield strength (YS) 50% higher than those of base metal and with ultimate tensile strength up to 380 MPa were achieved.

Keywords:
Welded joint; Friction Stir Welding; 7075-T651 Aluminum Alloy; Microstructure; Mechanical properties