Microstructural evolution and strengthening mechanisms of a high-strength Al-Mg-Si alloy processed by laser powder bed fusion and ageing treatment

In this work, the processability, microstructural evolution and mechanical properties of a novel crack-free Al -5.3 wt% Mg -3.3 wt% Si alloy fabricated by laser powder bed fusion (LPBF) were investigated systematically. The Al5.3 wt% Mg -3.3 wt% Si alloy with low solidification range exhibits good processability and reaches a high relative density of 99.6% at the VED of 103.3 J/mm(3). The hierarchical microstructure was featured by the fine alpha-Al matrix that contains the interaction between the nanosized Mg2Si eutectic and high-density dislocations in the as-LPBFed alloy, which delivers high yield strength of 374 MPa and elongation of 5.8% under as-LPBFed condition. The yield strength is further enhanced to 433 MPa under as-aged condition of 180 C for 6 h. The property enhancement is associated with the precipitation of beta'' and beta phase. However, the broken and coarsened Mg2Si eutectics as well as the reduction of dislocation density result in strength degradation after ageing exceeds 300 C-degrees.