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

Abstract

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 Al-5.3 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/mm3. The hierarchical microstructure was featured by the fine α-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 β'′ and β 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.