Bespoke multi-step homogenization heat-treatment for a laser powder bed fused AlSi10Mg4Cu alloy synthesized via in-situ alloying

Abstract

Although in-situ alloying is a flourishing technique for developing novel metal alloys for Laser Powder Bed Fusion (LPBF), the mixed alloying elements regularly segregate, causing a heterogeneous chemical composition enriched with new metastable phases. Hence, the present study focuses on the homogenization of an in-situ alloyed AlSi10Mg4Cu metal system by pursuing various heat-treatment pathways. We firstly investigated the alloy homogenization behavior upon conducting single-step heat-treatments at 485, 500, and 515 °C for set times. Experimental findings revealed that the alloy was challenging to homogenize in one-go. Heat-treating at 485 °C did not enable the complete dissolution of Cu-rich phases. By increasing temperature at 500 °C, the alloy was neither homogenized nor near-fully dense due to the untimely incipient melting of metastable Q-Al 4 Cu 2 Mg 8 Si 7 phase which caused pores. Lastly, homogenization at 515 °C led to the enhanced dissolution of θ -Al 2 Cu phase and its precursors but simultaneously exacerbated the incipient melting process of Q-Al 4 Cu 2 Mg 8 Si 7 phase observed at 500 °C. Based on the analyses of single-step homogenization behaviors, we designed a multi-step homogenization heat-treatment to dissolve the low-melting Q- phase selectively avoiding its deleterious incipient melting. The material underwent then a homogenization treatment with three consecutives steps at 495 °C for 4 h, 505 °C for 6 h and 515 °C for 6 h. The homogenization response was satisfying this time: incipient melting of Q-Al 4 Cu 2 Mg 8 Si 7 phase was annihilated, and Cu solubilization was greatly enhanced. The supersaturation level was comparable with that of the as-built condition, i.e., optimal for following age-hardening treatments. • AlSi10Mg + 4Cu alloy is produced by LPBF in-situ alloying. • Various heat-treatment pathways are investigated to homogenize the alloy chemical composition. • Single-step homogenization at 485 °C did not entirely dissolve θ -Al 2 Cu phase; • Single-step homogenization at 500 °C partially solubilized θ - phase but induced early-stage incipient melting of Q-Al 4 Cu 2 Mg 8 Si 7 phase; • Single-step homogenization conducted at 515 °C dissolved θ -Al 2 Cu while causing incipient melting of Q- phase; • Multi-step homogenization solubilized Cu segregations avoiding incipient melting of Q- phase.