Investigation of weldability and microstructure-mechanical properties of AA5XXX and AA7XXX aluminum alloys by cold metal transfer (CMT) method

5xxx series aluminum alloys are widely used in the automotive industry, and 7xxx series aluminum alloys have recently started to be preferred in parts requiring strength. At this point, studies on the welded joining process of both alloys have gained importance recently. Therefore, in this study, non-pulsed (65, 75, 85 amperes) and pulsed (P) (100, 110, 120 amperes) cold metal transfer (CMT) welding was applied to different aluminum alloys couples EN AW 5754 H111 and EN AW 7075 T6 sheets using silicon-reinforced ER 4043 (AlSi5) welding filler wire with different current. Macrostructure, microstructure examinations, microhardness, tensile and bending tests were applied to the samples. No macro porosity formation was observed, except for the sample welded in non-pulse mode at the lowest current value. It has been observed that the structures in the weld zones have a typical eutectic structure. It was observed that the structures consisted of dendrite/semi-dendrite and equiaxed grains. In microhardness tests, all samples showed similar results. The highest average microhardness value in the weld zone was measured as 101 HV in the pulsed sample welded at 100 amperes. As a result of tensile tests, the highest strength values are approximately 170 MPa in pulsed mode and 122 MPa in non-pulsed mode. All samples broke from the weld metal as expected. When the fracture surfaces were examined, a ductile fracture type was observed in the joining samples. In the cap and root bending test results, some samples bent 180°, while some samples broke without bending. As a result of all tests and examinations, the sample combined with a current of 110 amperes in pulsed mode showed the best results. It has been observed that the ER4043 filler wire used can provide the desired joints for such joints, but it exhibits lower strength values in the weld metal strength values than the main materials, as expected.