Influence of Alloys Position, Rolling and Welding Directions on Properties of AA2024/AA7050 Dissimilar Butt Weld Obtained by Friction Stir Welding

Jorge Dos Santos,Alessandro Barbini,Jan Carstensen

doi:10.3390/met8040202

Abstract

Friction stir welding (FSW) was carried out for the butt joining of dissimilar AA2024-T3 and AA7050-T7651 aluminium alloys with 2-mm thicknesses. A comparison between the position and orientation of different materials was performed by varying the welding speed while keeping the rotational speed constant. Through an analysis of the force and torque produced during welding and a simple analytical model, the results indicate that the heat input was reduced when the AA7050 alloy was located in the advancing side (AS) of the joint. The different material positions influenced the material transportation and the interface in the centre of the stir zone (SZ). The microhardness of both materials was lower when they were in the AS of the joint. The differences in the hardness values were reduced at higher welding speeds when the heat input was decreased. The mechanical performance increased when the lower strength alloy was located in the AS. The material orientation exhibited a small influence when the AA7050 alloy was in the AS and in general on the resulting microhardness for all the cases analysed. The tensile strength values were very similar for both orientations, but an increase in the yield strength could be measured when the materials were oriented in the transverse direction.

Highlights

In aeronautical structures, the joining throw riveting or adhesive bonding of dissimilar materials is a common practice, which is necessary to increase the mechanical performance of machines [1,2].The problems associated with these types of joining techniques, which are well known and widely used, are related mainly to the increase in weight, the high costs of the assembly and spare parts and the difficulty in the development of an efficient automatic process for the installation.Friction stir welding (FSW), since its invention in the 1991 at The Welding Institute (TWI Ltd., Cambridge, UK) [3], has been seen as a competitive technique for joining dissimilar materials with a good consistency in mechanical properties at a high productivity
The resulting microstructure and material properties developed were analyzed in depth to have a clear understanding and of the material properties developed were analyzed in depth to have a clear understanding of the joint joint performance
An analysis of the process showed a reduction in the heat generated with the AA7050-T7651 material positioned in the advancing side (AS) of the weld caused by a general decrease in the torque

Summary

Introduction

The problems associated with these types of joining techniques, which are well known and widely used, are related mainly to the increase in weight, the high costs of the assembly and spare parts and the difficulty in the development of an efficient automatic process for the installation. Friction stir welding (FSW), since its invention in the 1991 at The Welding Institute (TWI Ltd., Cambridge, UK) [3], has been seen as a competitive technique for joining dissimilar materials with a good consistency in mechanical properties at a high productivity. Dissimilar welds of AA6061 and AA7075 obtained by FSW have been previously studied [6], focusing on the processing parameters and the position of the materials. Dissimilar welding involving an aluminium 6XXX series alloy was investigated previously by Amancio-Filho et al [7] without

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