Characterization of newly developed semisolid stir welding method for AZ91 magnesium alloy by using Mg-25%Zn interlayer

Semisolid stir joining of AZ91 alloy was investigated by using mechanical stirring and Mg-25 wt%Zn interlayer. A 2 mm-thick interlayer was located between two 7.5 mm-thick AZ91 pieces. Then, they were heated to 530 °C, the semisolid temperature of both base metal and interlayer. A stirrer with a rotational speed of 1600 rpm was introduced into the weld seam. Optical microscopic and scanning electron microscope (SEM) investigation, microhardness test, shear punch test (SPT), and three points bending test were carried out to assess the properties of the joint. Results showed three distinctive zones: stir zone (SZ), compacted zone (CZ), and diffusional-mechanical affected zone (DMAZ). SEM and X-ray diffraction (XRD) analysis also indicated a wide range of compounds formed in the different zones. The macroscopic image also showed advancing and retreating sides with different DMAZ widths. Proper metallurgical bonding was achieved due to the satisfactory mixing of base metal and interlayer in the semisolid condition. Shear punch test also showed decent ultimate shear strength of the weld metal.