Investigating the weld joint characteristics of AZ31 and AZ91 magnesium alloys produced by friction stir welding

In this work, FSW was used to join AZ31 and AZ91 magnesium (Mg) alloys to investigate the mechanism behind joint formation and its mechanical performance. The cross-sectional microstructure of the weld zone clearly indicated a strong metallurgical bonding between AZ31 and AZ91 sheets in addition to the mechanical interlocking due to the mixing of both base materials. Uniform hardness (62.9 ± 4.5 HV) was recorded in the weld joint and the values were between AZ31 (59.8 ± 2.4 HV) and AZ91 (78.7 ± 19.5 HV). Tensile test results demonstrated decreased strength (145 ± 4.2 MPa) compared with the base alloys (265 ± 7.3 MPa and 190 ± 4.8 MPa for AZ31 and AZ91, respectively. Ductility was noticed as decreased as reflected by the lower % of elongation for the weld joint compared with both AZ31 and AZ91 base materials. The fractography studies of the samples suggest a brittle mode of fracture in the weld joint similar to that of AZ91 base material.