Effect of friction stir processing on microstructure and properties of AZ91 magnesium alloy CMT cladding layer

•FSP can significantly refine the grains of the cladding layer.•The β-Mg17Al12 phases homogeneously disperse into the matrix after FSP.•The corrosion resistance of the cladding layer is improved via FSP.•FSP can significantly strengthen the tensile strength and ductility of the cladding layer. AZ91 magnesium alloy cladding layer obtained by cold metal transfer technique was subjected to friction stir processing (FSP). The results showed that, after FSP, the grains of the deposited layer were significantly refined, and the coarse β-Mg17Al12 phase was broken and dispersed into the α-Mg matrix, leading to the microstructure modification. Compared with the unprocessed cladding layer, the FSPed samples exhibited better corrosion resistance. Due to the grain refinement and disintegration of the second phase, the tensile strength and elongation of the cladding layer after FSP increased from 233.4 MPa and 5.6% to 278.5 MPa and 13.4%, respectively.