Abstract
The aim of this work is to evaluate the difference between the properties of several aluminum alloy joints welded with the traditional air-cooled friction stir welding process and others obtained by the combination of the traditional friction stir welding setup with a water-cooling system. In particular, precipitation-hardening alloys AA2024-T3, AA6082-T6 and AA7075-T6, and a work-hardening alloy, AA5754-H111, were taken into account. From Rockwell and Vickers hardness maps, it was possible to observe a clear dependence of the hardness distribution on the cooling systems; joints obtained using a water-cooling system showed higher values of hardness, reached in the central zone and a narrow area interested by the hardness reduction for all the tested alloys. From tensile tests executed orthogonally to the welding direction, it was possible to observe that the alloys have responded differently in terms of ultimate tensile strength and final elongation when the water-cooling system was used. The microstructural analysis of the three precipitation-hardening alloys showed a larger average grain size in the nugget zones for the water-cooled condition. Moreover, in the thermo-mechanically altered zones of the water-cooled AA6082 and AA7075 joints, the grains were characterized by a smaller average size than the grains of the same air-cooled welds.
Highlights
Aluminum has proven to be a material of considerable interest in engineering, especially in the aeronautic and automotive sectors, because of its advantageous ratio between mechanical properties and weight
For this work-hardening alloy, the percentage elongation was found to be on average higher for water-cooled welds than those air-cooled and, in particular, it was possible to observe that in the water-cooled joints the point of failure is placed in the base material, away from the welded area
The paper reports the results of the investigations of the effect of a water-cooling system on the mechanical properties and microstructural characteristics on Friction Stir Welding (FSW) joints made of different alloys: precipitation-hardening alloys AA2024-T3, AA6082-T6 and AA7075-T6, and work-hardening alloy
Summary
Aluminum has proven to be a material of considerable interest in engineering, especially in the aeronautic and automotive sectors, because of its advantageous ratio between mechanical properties and weight Significant importance in these fields is assumed by the aluminum precipitation-hardening alloys, which can achieve mechanical properties comparable to those of structural steel [1,2]. By carrying out a solubilization quench, that is moving in the solubility field with sudden cooling, the dispersion of the alloy elements is obtained in the form of clusters These clusters split up to give nano-metric precipitates dispersed in the matrix that allow these alloys to reach the mechanical characteristics that distinguish them, by preventing the movement of the dislocations [4].
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