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• Effects of porosity distributions on the tensile and fatigue properties were studied. • Porosities appeared near the fusion line in the arc zone with high arc current. • Low welding speed or arc current was benefit for reducing the porosity rate. • Fracture locations of the tensile specimens were mainly related with the porosity rate. • Fracture diverted from ductile to ductile and brittle mixed mode as porosity increased. 6082-T6 aluminum alloy with thickness of 6 mm were welded by laser-MIG hybrid welding. The effects of welding parameters on the porosity distribution, the correlations between the porosity distribution and mechanical properties were comprehensively investigated. The porosities mainly appeared near the fusion line of the arc zone when the arc current larger than 140 A, and which mainly existed in the center of the laser zone with other unsuitable parameters. Adopting low welding speed and setting heat source distance as around 3 mm were beneficial for the reduction of the porosity rate. The laser power, defocus distance, fit-up gap and gas flow rate had less effects on the porosity distribution. The average tensile strength of the joints without porosities was 260 MPa, which decreased to 224 MPa and 202 MPa as the porosity rate increased to 5.1% and 8.9%. The tensile specimens fractured at the heat affected zone or in the weld center when the porosity rates less or greater than 3%, and the fracture feature was diverted from ductile fracture to ductile and brittle mixed mode as the porosity rate increasing. The fatigue strength reduced from 113 MPa to 56 MPa when the porosity rate increased from 0% to 8.9%, while the porosity position had little effect on it. The fracture initiated in the weld surface when the joints without porosity, and which initiated near the porosity when the porosities existed in the joint. [ABSTRACT FROM AUTHOR]

Aluminum profile structures are extensively used in the transportation industry and pose a considerable challenge to single-sided spot joining technologies. The widely used Huck BOM® riveting process requires prefabricated holes and thus significantly increases cost and reduces efficiency. In this study, a novel single-sided friction riveting (SSFR) process with an internal-threaded semi-tubular rivet is proposed to realize a screwed-solid state hybrid joining of aluminum sheet to profile structure without prefabricated holes. The results show that the upper trapped metal is welded with the lower profile structure under the thermal-mechanical coupled action generated by rivet stirring. The internal thread could facilitate material filling into the rivet cavity and form a mechanical interlock, so as to realize the single-sided joining between the sheet and the profile without prefabricated holes. The one-stage SSFR process could form shear texture and promote continuous dynamic recrystallization, but lead to excessive material softening and internal cracking. A two-stage process including friction softening and screw tightening could better coordinate the effects of heat and force, thereby avoiding cracking and refining grains in the stirring zone. Finally, the tensile-shear and cross-tension peak loads were respectively improved by 9.0 % and 29.3 %, compared to the joints with one-stage process and non-structural rivet. [ABSTRACT FROM AUTHOR]