Modifying microstructures and mechanical properties of laser-arc welded joints of dissimilar advanced aluminum alloys

In this paper, two dissimilar aluminum alloys (AA), AA5083 and AA6082, have been joined via fiber laser-MIG welding method using two different filling wires (ER4043 and ER5356). The heat input for producing joints with ER5356 and ER4043 is respectively 289.36 J/mm and 293.38 J/mm. The microstructures are characterized from testing of SEM, EDS and EBSD. Results show that joints using ER4043 wire (referred as ER4 joints) have finer microstructures in terms of smaller grain size (49 +/- 63 mu m) and higher dislocation density (1.25 x 10(13) m(-2)). The average microhardness in fusion zone (FZ) of ER4 joints is 82 HV, which is greater than that of joints using ER5356 wire (referred as ER5 joints). However, the ultimate tensile strength (UTS) of ER4 joints are weaker than that of ER5 joints, with the UTS of ER4 and ER5 joints being 220 MPa and 232 MPa, respectively. Strengthening mechanisms in these two types of joints are quantitatively presented via a strength model, which can well reproduce the yield strength of these two types of joints. With molecular dynamic simulation, it is revealed that the loss of mechanical properties of ER4 joints is caused by the high density of pores in its FZ, since these pores lead to serious stress concentration under external uniaxial loading.