Processing, microstructure, and mechanical behavior of AZ31 magnesium alloy fabricated by electron beam additive manufacturing

In this work, AZ31 magnesium alloy was successfully manufactured by the electron beam additive manufacturing (EBAM) technique. The microstructure and mechanical properties of the EBAM samples under different energy densities and deposition passes were analyzed. The results show that the energy density has a decisive effect on the manufacturability of the sample, wherein the sample prepared at an energy density of 1.432 × 10¹⁰ J·m^-3 possesses the best manufacturability. The thermal cycling of the EBAM technique resulted in apparent grain size variation and layered arrangement along the deposition height. The fine grains with an average size of approximately 20 µm account for 30% of the sample while the remaining coarse grains possess an average size of approximately 40 µm. Moreover, a large number of fine Al₈Mn₅ and Mg₁₇Al₁₂ phases precipitated due to the high cooling rate of the molten pool. The microhardness of the sample first decreased and then increased slightly with increasing deposition height. Under the combined effects of dispersion strengthening and grain refinement, the EBAM specimens demonstrated excellent tensile strength and elongation of 230 MPa and 13.5%, respectively, which are superior to those of the die-cast AZ31 alloy.