The high quality joints fabricated by laser arc hybrid welding have certain differences in the crosssectional geometry of the weld seam. In order to study these differences quantitatively

the back width to surface width ratio (R

w

) was proposed. Based on the optimization experiments of 7050–T7451 high-strength aluminum alloy with 3 mm thickness by laser arc hybrid welding

three typical welded seams were selected to investigate the correlation effect of different R

w

on the macroscopic formation

microstructure

microhardness and tensile properties

of the joints. The results show that

only when the Rw exceeds a certain threshold

the weld width on both sides becomes more uniform

and porosity defects are effectively controlled. The microstructure characteristics of the weld zone from the fusion zone to the center of the weld are fine grains layer

columnar dendritic and large-scale equiaxed grains

respectively. With the R

w

increasing

the width of the columnar dendritic structure gradually decreases until it disappears

while

the average grain size at the center of the weld seam gradually increases

and the tensile properties of welded joints increase firstly and then decrease. When the R

w

is about 0.70

the tensile properties reach the best

with an average ultimate tensile strength of 390 MPa and elongation after fracture of 2.9%. The tensile fractures present a mixed fracture characteristic dominated by brittle fracture.