A research team from Skoltech (part of the VEB.RF group) and other scientific organizations in Russia and India has conducted a systematic study of the laser powder bed fusion (PBF-LB) process for aluminum bronze. This material is significantly important for components operating under intense thermal loads that require efficient heat dissipation — such as heat exchangers, cooling elements of power plants, and power electronics enclosures. The findings, published in the journal Materials Characterization, pave the way for manufacturing complex-shaped components using laser powder bed fusion that match the strength and thermal conductivity of traditionally cast parts, and in some cases, even exceed them.
Aluminum bronze (Cu-9.5Al-1Fe) offers higher thermal conductivity than steel and titanium while being more suitable for additive manufacturing than pure copper. However, printing copper alloys presents two fundamental challenges: the material’s high reflectivity and its rapid heat dissipation. These factors lead to the formation of defects — specifically, lack-of-fusion pores, which occur when powder particles fail to melt completely, and so-called keyhole porosity, caused by the formation of a deep, unstable vapor depression in the melt pool that produces voids upon solidification.
During the experiments, the scientists varied the energy density (from 125 to 938 J/mm³) by adjusting the laser power (90–150 W) and scanning speed (100–600 mm/s). They established that at low energy densities, lack-of-fusion pores dominate, while at high energy densities, keyhole pores — typical of an unstable deep penetration mode — become prevalent. The overall porosity level remained around 5% across all tested regimes.
Despite the presence of residual porosity, the printed samples demonstrated mechanical properties exceeding those of cast aluminum bronze. The ultimate tensile strength reached up to 748 MPa, and elongation reached up to 16.2%, approaching the parameters of nickel-aluminum bronze (Ni-Al-Bronze), which is traditionally used in heavy-duty applications.
“We were able to show that even using equipment with limited laser power, it is possible to achieve mechanical properties close to those of industrial nickel-aluminum bronzes. The key factor turned out to be not just increasing the energy input, but understanding the mechanisms governing the transition between different types of defects. This allows us to predict material properties at the stage of selecting printing parameters,” shared Associate Professor Stanislav Evlashin from the Materials Center, a co-author of the study.
The authors paid particular attention to changes in the phase composition. The ultra-fast crystallization inherent to laser melting produced phases atypical of the equilibrium structure of aluminum bronze, specifically Al₂Cu interlayers and Cu₃Fe nanoparticles. The study also showed that increasing energy density reduces the phase fraction primarily responsible for the material’s hardness and strength, which conversely has a negative impact on electrical and thermal conductivity. These structures and phases form due to cooling rates reaching up to 10⁷ K/s and influence the balance between strength, ductility, and thermal properties.
“Using a set of approaches — from microstructural analysis using various microscopy techniques to measurements of physical and mechanical characteristics — we established a direct correlation between dislocation density, thermal conductivity, and electrical conductivity. It turns out that as energy input increases, dislocation density decreases and a redistribution of aluminum occurs within the structure. This leads to higher thermal conductivity without any noticeable degradation in mechanical properties. Porosity, meanwhile, has a minor effect,” explained Anastasia Filippova, the first author of the paper and a PhD student in the Mathematics and Mechanics program at Skoltech.
Thermal conductivity measurements were carried out over a wide temperature range — from 5 to 575 K — using two independent methods: PPMS and laser flash analysis. The authors demonstrated that the thermal conductivity of samples produced with high energy density reaches 47 W/(m·K) at room temperature. This is comparable to values for cast material but was achieved with significantly higher strength.
