Microstructure and Mechanical Properties of Selective Laser Melted Al–2.51Mn–2.71Mg–0.55Sc–0.29Cu–0.31Zn Alloy Designed by Supersaturated Solid Solution

Selective laser melting(SLM)of aluminium alloys for lightweight application is arousing widespread interest,but the available alloy compositions are limited due to unsatisfactory mechanical performances.The rapid solidifi cation of SLM provides a pathway to design a novel alloy composition with extended solubility.This strategy is demonstrated by an additively manufactured novel Al–2.51 Mn–2.71 Mg–0.55 Sc–0.29 Cu–0.31 Zn alloy with the supersaturated solid solution in the present study.The microstructure of as-build sample is characterized with multi-modal grains with the fi ne equiaxed grain(FEG,~800 nm)at molten pool boundaries,coarse equiaxed grain(CEG,~2μm)and columnar dendrites(CD,~4μm)inside the molten pool,which relates to the precipitations type and distribution.It is observable that Al 3(Sc,Zr)precipitation particles with the size of~50 nm are dispersed in the FEG zone,while the interior of CEG shows no Al3(Sc,Zr)particle which only exists at the CEG boundaries.Regardless of FEG,CEG or CD,the slender Al6 Mn precipitation with the length of~500 nm is distributed along the grain boundaries.Meanwhile,a lot of vacancies and thickness fringes are detected in the FEG zone,which confi rms the supersaturated solid solution in laser rapid solidifi cation.The ultimate tensile strength and yield strength of the as-printed sample are~380 MPa and~330 MPa,respectively,with elongation~14%,which increase to~440 MPa and~410 MPa with a reduction of elongation to~9%after heat treatment.