For hot extrusions of magnesium alloy sheets, Dissimilar AZ80 and AZ31 were used, in which AZ80 was
placed on advancing side and AZ31 on retreating side, using friction stir butt welding with different process parameters.
Some defect-free welded joints with good weld surfaces could be obtained with some suitable welding conditions. The
maximum tensile strength of welded joint which is 225.5 MPa can reach 98% that of the AZ31 base material. Influence of
process parameters on defects, weld shaping and mechanical property were discussed systematically. And the
microstructure of different zones was compared. The fracture of the welded joints takes place at the junction of
mechanical heat affected zone and nugget zone in AZ31 magnesium alloy set retreating side, since existing difference in
metallographic structure of alloy diversely suffered by heat, pressure and depositing impurities. Fracture initiation site
may be the P line defect which should be eliminated, and the P line defect formation was analyzed.