Abstract: 8 mm thick 5083 aluminum alloy is penetrated fully without sloping and filler by double-sided synchronization vertical welding(DSSVW). The welding heat input distribution of both sides, the microstructure and the mechanical properties of the welding joints are analyzed to show joining mechanism. Results indicate that the thermal input of DSSVW is acceleratedly accumulated and the penetration increases by the growth velocity of cubic function. The morphology of DSSVW is hyperbolic type, while the morphology of single side vertical welding(SSVW) with the same heat input is inverted saddle type. If the total heat input is certain, an increase in the energy distribution coefficient will cause an increase in front bead wide, a decrease in back bead wide of DSSVW process, while the intermediate weld wide is almost unchanged and the melting area first increases then decreases. The weld wide and fusion area both decrease with the increase in welding velocity when the energy distribution coefficient is determined. The microstructure of base metal is banding fiber texture. Static recovery or recrystallization occurs in heat-affected zone(HAZ) due to arc heating, so that deformed microstructure disappeared and recrystallization grain generates. The weld metal zone is constituted by -Al solid solution, β phase(Al8Mg5) and skeleton shaped Mg2Si phase. The tensile strength decreases slightly with the increase in energy distribution coefficient, and the fracture mode is ductile fracture. The hardness of HAZ decreases and the hardness of the intersection region is lower than the front weld bead.

Key words: double-sided synchronization vertical welding(DSSVW), metallurgical structure, micro vickers hardness, single side vertical welding(SSVW), tensile strength, the energy distribution coefficient, weld joint morphology