The pulse current cold arc MIG welding of AZ31 Mg/5A05 Al heterogenous butt joint is carried out by filling SAl5183 wire. The microstructures and tensile strength of the joint were studied by scanning electron microscope

X-ray diffraction and tensile test. The results show that crack-free AZ31 Mg/5A05 Al heterogeneous joints can be achieved by the operated welding process. Complex weld is formed near the magnesium side. α–Mg cellular crystals

α–Mg+Al

12

Mg

17

feather like eutectics

Al

12

Mg

17

dendrites

Al

12

Mg

17

+Al

3

Mg

2

eutectoid structure

granular α–Al + Al

3

Mg

2

eutectic structure

island α–Al + intercrystalline Al

3

Mg

2

eutectic structure are formed orderly from the magnesium base metal side to the middle of the weld. The mid-weld and the weld near aluminum side are mainly composed of α–Al solid solutions. Nonuniform microhardness distribution across the weld is observed. The microhardness of the weld near the magnesium side is much higher than other regions due to the existence of Mg–Al intermetallic compounds. The fracture happened in the weld near magnesium side in the brittle fracture mechanism during the tensile test. The ultimate tensile strength of the joints reaches 93 MPa.