Single track scanning experiment on the hypereutectic aluminium alloy Al-8%Zn-7%Ni-3%Mg

Abstract

Solidification path, hot tearing susceptibility and processability by L-PBF of the hypereutectic aluminium alloy Al-8%Zn-7%Ni-3%Mg were investigated. It was shown that the alloy has an advantageous hot tearing resistance due to formation of an adequate amount of the [(Al)+Al3Ni] eutectic and a reduced effective solidification range. In that sense, it may be valid for L-PBF. To prepare a feedstock for L-PBF, we produced chips which were subsequently grinded by high-energy ball milling into a 100 µm fine powder batch. The powder contained irregular shape particles that may have led to failure in fabrication of regular single tracks at a laser power of 170-250 W and scanning speed of 200-350 mm/s. Whilst from on-top view all the tracks had defects like balling and irregularity, their cross-sections also revealed a high degree of penetration into 5052 alloy substrate. Most structures showed a level of mixing of 5/1 between the substrate and the experimental alloy. The most successful track obtained at 250 W and 250 mm/s showed an inhomogeneity in distribution of the alloy-rich regions. Meanwhile, no defects and no primary Al3Ni phase were observed. The present study serves as an initial one for further research which may be focused on producing of a finer powder, assessment of different layer thicknesses and fabrication of bulk specimens.