Summary The present study examines a friction stir welded 2017A aluminium alloy. Transmission electron microscope investigations of the weld nugget revealed the average grain size of 5 μm, moderate density of dislocations as well as the presence of nanometric precipitates located mostly in grains interiors. Scanning electron microscope observations of fractures showed the presence of ductile fracture in the region of the weld nugget with brittle precipitates in the lower part. The microhardness analysis performed on the cross‐section of the joints showed fairly small changes; however, after the artificial ageing process an increase in hardness was observed. The change of the joint hardness subject to the ageing process indicates partial supersaturation in the material during friction stir welding and higher precipitation hardening of the joint.

No abstract

No abstract

In order to obtain ultrafine grained structure, commercially pure aluminium (Al 1050) plates were subjected up to 8 passes of Incremental Equal Channel Angular Pressing (IECAP) following route C. Plates in different stages of IECAP were joined using Friction Stir Welding (FSW). All welded samples were investigated to determine their mechanical properties and structure evolution in the joint zone. The joining process reduced mechanical strength of material in the nugget zone, which was explained by the grain growth resulting from temperature rise during FSW. Nevertheless, the obtained results are promising in comparison to other methods of joining aluminium

Dissimilar aluminum alloy plates of 2017A-T451 and 5083-H111 were friction stir welded in a butt joint configuration along the longitudinal direction. Welding trials demonstrated that placing 5083 on the advancing side enhanced material flow and consequently formed a larger weld nugget. Numerical simulation supported this observation through analysis of volumetric flow rates through reference planes surrounding the stir zone. The analysis also suggests that the weld configuration that results in a decreasing temperature-dependent flow stress in the weldment from the leading edge of the tool to the trailing edge will maximize material flow in dissimilar friction stir welding welds. The decreasing flow stress promotes material flow along the retreating side of the tool as flow conditions necessarily become easier from the front to the back. Regardless of its position during welding, however, 2017A alloy dominated the nugget region. In either weld configuration, alternating bands of 2017A and 5083 with similar grain sizes (approximately 10 µm) comprised the weld microstructure. Within the nugget, numerous second-phase particles as well as dislocations occurring as single dislocations or in the form of dislocation tangles or walls (low angle grain boundaries) were present. The relatively high dislocation density observed in both alloys suggested that recrystallization was incomplete. Hardness mapping revealed an asymmetric variation of hardness across the weld centerline that strictly corresponded to the distribution of particular alloys within the nugget. During tensile testing, the AS 5083-RS 2017A configuration failed under ductile shear rupture occurring in the base 5083 material far from the weld. For the opposite configuration, the tensile samples ruptured perpendicular to the load axis exactly on the border between the nugget and the thermomechanically affected zone on the 2017A alloy side.