Microstructure and mechanical properties of pseudo binary eutectic Al–Mg2Si alloy processed by laser powder bed fusion

Abstract

The traditional wrought Al–Mg–Si alloys fabricated via laser powder bed fusion (LPBF) are prone to hot cracks, unless adding grain refiners in as-LPBFed Al alloys. In this work, the Al-9.6 wt.%Mg-4.9 wt.%Si (equivalent to pseudo binary eutectic Al-13.3 wt.%Mg2Si) alloy with low solidification range and hot-cracking susceptibility was successfully processed by LPBF. The as-LPBFed alloys have reached a high relative density of 99.3% at the VED of 129.6 J/mm3. The microstructures were featured by fine α-Al grains and cellular eutectic Mg2Si, accompanied by a high number density of dislocations, coherent GP zone and α-Al12(Fe,Mn)3Si phases. The as-LPBFed Al-13.3Mg2Si alloy exhibited the high ultimate tensile strength of 557 MPa, yield strength of 439 MPa and elongation of 2.9%. In addition to the grain refinement and dislocation strengthening, the strength enhancement is mainly ascribed to the dispersion strengthening from the divorced nanosized eutectic Mg2Si. The results demonstrate that manipulation of alloys at near eutectic composition is effective to achieve high strength Al–Mg–Si alloys processed by LPBF.