Effect of rotation rate on microstructure and mechanical properties of CMT cladding layer of AZ91 magnesium alloy fabricated by friction stir processing

Cladding layers of AZ91 magnesium alloy obtained by cold metal transfer (CMT) technique were subjected to friction stir processing (FSP) with different rotation rates. The experimental results showed that the FSP could significantly refine the crystal grains of the cladding layer, and cause the coarse second phases to be crushed and dissolved into the alpha-Mg matrix at the same time. As the rotation rate increased, the peak temperature of the stirring zone gradually increased, leading to an increase in the average grain size of the stirring zone. There was no obvious difference in the distribution of the second phase, all of which were dispersed into the alpha-Mg matrix in the form of granules. Compared with the cladding layer before FSP, the microhardness and tensile properties of the processed cladding layer under each parameter were both significantly improved due to the combined effects of fine-grain strengthening and second phase dispersion strengthening. In addition, the average microhardness, tensile strength and elongation of the stirring zone all increased first, and then decreased with the increase of the rotation rate.

Automated summary

This study conducted friction stir processing on the cladding layers of AZ91 magnesium alloy, and found that FSP could refine the crystal grains, crush and dissolve the coarse second phases into the matrix, and significantly improve the microhardness and tensile properties.