The laser-MIG composite welding was used to weld Q960 steel/6061 aluminum dissimilar metal

and the microstructure

phase composition and mechanical properties of the composite welded joint before and after adding Cu were analyzed comparatively

and the fracture morphology was observed.The results reveal that the weld joint remains the typical melt brazing characteristics after Cu addition

and the interface layer of the IZ region presents obvious change

where the thickness of the interface layer is decreased from 16μm before adding Cu to 6μm after adding Cu

and the needle like Fe

4

Al

13

phase and the tongue Fe

2

Al

5

phase in the interface layer are transformed into fine block Al

13

（Fe

Cu）4 and tongue Al

5

（Fe

Cu）2

and microcracks in the interface layer disappear.The maximum hardness of the steel/aluminum composite welded joint after adding Cu still occurrs in the interface layer

however the maximum hardness is reduced significantly

which is mainly related to the formation of Al

13

（Fe

Cu）4 and Al

5

（Fe

Cu）2 intermetallic compound in the interface layer.After adding Cu

the tensile strength and elongation of welded joints are increased by 110.5% and 183.3%

respectively

compared with those of ones before Cu addition

while the fracture locations are all located at the steel/aluminum interface region.