Microstructure Features and Mechanical Properties of Double-Sided Friction Stir Welded Joints of AA2050-T84 Thick Plates

F F Santini,A H Plaine,M H Miyazaki,J F Dos Santos,N G De Alcântara,C R M Afonso,L Bergmann

doi:10.1590/1980-5373-mr-2020-0309

Abstract

Abstract As part of an ongoing process to fully assess the potential for friction stir welding (FSW) to be used in the aerospace industry, an attempt was made to produce double sided FSW joints at traverse speeds equal or higher than 5 mm/s of AA2050-T84 12.7 mm thick plates for high-volume production applications. With an emphasis on weld quality, the local and global mechanical properties were evaluated and correlated with microstructure of the welding area. Sound welds with no volumetric defects were obtained for tool traverse speeds up to 12 mm/s, resulting in yield and ultimate tensile strengths corresponding to 65% and 77% of base material, respectively. The metallurgical and mechanical characterization demonstrate that density of Cu-rich precipitates has a first order effect on micro-hardness variation. In the stir zone the dissolution temperature of this precipitate is achieved and its volume fraction is greatly reduced. The remaining precipitates seems to be partially dissolved and undergone a significant thickening at the welding zones in which the process temperature has not reached the dissolution temperature. Weld fractures after tensile tests were observed to start in the region of hardness minima.

Highlights

In the last decade, new aluminum alloys for aerospace applications have been developed based on the Al–Cu–Li system, presenting significant improvement in required properties for structural performance: reduction in density, stiffness increase, increasing in corrosion resistance and increasing in fracture toughness and fatigue growth resistance
It is worth to mention that weld pitch (WP) below 0.6 mm/rev requires very high rotational speeds to obtain traversing speeds equal to or higher than 5 mm/s, causing excessive material softening and flash generation
At a WP of 1.2 mm/rev, the DS-friction stir welding (FSW) tool probe broke due to the high stress levels experienced during the welding process

Summary

Introduction

New aluminum alloys for aerospace applications have been developed based on the Al–Cu–Li system, presenting significant improvement in required properties for structural performance: reduction in density, stiffness increase, increasing in corrosion resistance and increasing in fracture toughness and fatigue growth resistance. The difficulties in welding precipitation hardening aluminum alloys by fusion welding processes has hindered the development of new applications, opening a new avenue for the use of alternative joining technologies such as solid-state friction based-processes. Joining of aluminum alloys via friction stir welding (FSW) has been exceedingly successful. Materials Research temperature, the remaining T1 precipitates partially dissolve and undergo a significant thickening. A direct correlation was observed between the precipitates and micro-hardness measurements

Methods

Results

Conclusion