Microstructure and mechanical properties of aluminium alloy cellular lattice structures manufactured by direct metal laser sintering

Abstract

This study thoroughly investigated the microstructure and mechanical properties of AlSi10Mg periodic cellular lattice structures with a wide range of volume fractions (5–20%) and unit cell sizes (3–7mm) fabricated via direct metal laser sintering (DMLS). It was found that the arc-shaped melt pools are overlapping with each other and comprising near fully dense struts (relative densities≥99%) of the as-built lattice structures. The melt pools of the struts are characterized with very fine cellular-dendritic microstructure. Two distinctive zones in the melt pool can be distinguished: the boundary of melt pool possesses the coarse cellular/dendritic microstructure with the cell size or dendrite arm spacing ranging of 2–4µm, while the interior of melt pool exhibits the much finer cellular microstructure consisting of the 400–700nm cells mainly filled with the α-Al matrix and some embedded rod-type Si-phases, and the network boundaries predominantly generated by the aggregates of approximately 20nm Si particles. Both compression strength and microhardness decrease with the increase in the unit cell size when the volume fraction is fixed. This is mainly because the thinner struts of the smaller unit cell size lattice structures were cooled faster by their surroundings and then exhibit a higher cooling rate, leading to finer microstructure. The compression strength increases with increasing the volume fraction, and an equation based on the Gibson–Ashby model is established to estimate the compression strength of DMLS-produced AlSi10Mg gyroid cellular lattice structures with the 3mm unit cell size.