Microstructure Evolution of Al-Mn-Mg-Sc-Zr Alloy Prepared by Selective Laser Melting Before and After Heat Treatment

Al-Mn-Mg-Sc-Zr alloy was prepared by selective laser melting (SLM) technique. The microstructure of Al-Mn-Mg-Sc-Zr alloy before and after heat treatment was characterized by X-ray diffractometer, scanning electron microscope, energy dispersive spectrometer, and transmission electron microscope, and the hardness of the alloy was tested. Results show that the microstructure of as-deposited alloy is mainly composed of alpha-Al, Al-6 Mn, and primary Al3Sc phases. The SLMed molten pool presents the fish-scale shape, and a large number of fine equiaxed crystals are formed near the fusion line of molten pool with average grain size of about 0.57 mu m. The center of the molten pool is composed of columnar crystals with average width of about 0.48 mu m. The rodlike Al6Mn phase is mainly distributed along the grain boundary, and a small amount of granular primary Al3Sc phase exists inside the grain, which indicates that the primary Al3Sc can be used as heterogeneous nuclear particle to refine the alpha-Al matrix. After heat treatment, the size of equiaxed crystals and the width of columnar crystals in the molten pool are increased, and a large number of fine and dispersed secondary Al3Sc particles are precipitated in the structure. The hardness test results show that the hardness of the alloy is increased firstly and then decreased with prolong the aging durations at different temperatures. Compared with that of the as-deposited alloy, the hardness of the alloy after peak aging (325 degrees C/180 min) heat treatment increases by about 30%, reaching 1813.0 MPa.