EOS Alumide is a polyamide 12 powder feedstock in which fine aluminum particles are dispersed as a discrete filler phase for CO₂ laser sintering systems. The material is supplied in a grey metallic powder form and is processed at a nominal layer thickness of 0.15 mm on production laser-sintering platforms. The aluminum filler raises the density of the finished part to a supplier-reported typical value of 1.36 g/cm³ under ISO 1183-1; the same filler increases thermal conductivity relative to unfilled polyamide 12, with a supplier-reported value of approximately 0.5 W/m·K. Because the matrix remains polyamide 12, moisture uptake follows the behavior of the base thermoplastic: storage or handling in high-humidity environments above 60 % RH increases the risk of powder caking, irregular recoating, and laser melt instability. Pre-drying conditions specified by the powder supplier must be followed when flowability degrades or when moisture-sensitive melt processing occurs. Published data for the exact moisture equilibrium curve of this specific aluminum-filled feedstock are limited; operators typically monitor incoming powder mass and drying air dew point rather than relying on unfilled PA12 data.

How does the aluminum filler shift static mechanical response relative to unfilled PA12?

The dispersed aluminum phase increases stiffness at the expense of ductility. Table 1 lists supplier-published typical values for EOS Alumide in the as-sintered state at 23 °C; controlled laboratory atmosphere is maintained in accordance with ISO 291. The tensile modulus of 3800 MPa under ISO 527-1/-2 is approximately 2.3 times the modulus commonly reported for unfilled EOS PA2200 polyamide 12, while elongation at break falls to 4 %. The low elongation indicates notch-sensitive behavior and limited plastic deformation before fracture; Charpy data obtained under ISO 179-1/1eU show an unnotched value of 29 kJ/m², whereas the notched value drops to 4.6 kJ/m² under ISO 179-1/1eA. This shift is relevant when parts are loaded in bending or compression, where the higher flexural modulus of 3600 MPa under ISO 178 reduces deflection at equivalent wall thickness but increases the likelihood of brittle cracking under impact or repeated strain.

The stiffness-density trade-off is clearer when the Alumide data are placed beside unfilled and glass-filled polyamide 12 powders. Table 2 uses the same supplier-published typical values and test methods to separate the effect of filler type from base-resin identity. The unfilled EOS PA2200 offers lower density and greater elongation; the glass-filled EOS PA3200 GF raises the modulus relative to PA2200 but remains below Alumide, at 3200 MPa, while retaining a higher elongation at break of 9 %. The aluminum-filled grade therefore occupies a narrow band in which stiffness is prioritized over impact toughness and plastic flow. This difference is not simply a density correction; the aluminum phase also changes heat transfer, surface appearance, and machining response, which must be evaluated separately from static mechanical properties.

Recoater torque, part-bed temperature, and powder ageing in aluminium-filled SLS

The metallic filler changes process behavior in a production laser-sintering machine before the part reaches testing. Aluminum particles increase the bulk density of the powder bed and can raise recoat blade resistance; on machines operating with unfilled polyamide powders, the recoat speed and blade contact force are often set for lower-density polymers, so the aluminum-filled grade may require a lower recoat speed or a hardened recoater blade to avoid streaks and short feeds. The thermal conductivity increase means that the part bed loses heat to the machine frame and to freshly deposited powder more rapidly than unfilled PA12. If the part-bed setpoint is too low, edge curling and layer delamination occur; if the setpoint is too high, powder caking in the feed region and loss of flowability appear. Published data for the exact part-bed temperature window of EOS Alumide are machine-specific, but process engineers routinely verify the powder melt onset and crystallization behavior by differential scanning calorimetry under ISO 11357-1 before adjusting build chamber temperature. Powder ageing is a second process constraint. The aluminum phase can segregate during extended recycling because its density differs from the polyamide matrix; a feedstock blend of virgin and reclaimed powder must be monitored for density shift, melt flow index variation, and filler concentration. Without such monitoring, batch-to-batch variance produces parts with locally different stiffness and density.

Moisture in polyamide 12 at sintering temperature hydrolyzes the polymer and produces voids; the aluminum filler does not absorb water but does not shield the matrix from this reaction. Pre-drying with dry air at 80 °C is commonly specified until residual moisture is below a supplier-defined limit; water content can be checked by ISO 15512 Karl Fischer titration. Processing in an uncontrolled moisture environment above 60 % RH shortens the time before powder flowability and final part density degrade. The layer thickness of 0.15 mm constrains the minimum feature height resolution but not lateral resolution alone. Build orientation remains the strongest lever for anisotropy: tensile properties measured parallel to the build axis can differ from in-plane values, and published data for orientation-dependent mechanical properties of this particular aluminum-filled powder are limited. Orientation must be validated using printed test coupons per ISO 527-1/-2 before a new part geometry is released to production.

Powder handling and ignition risk are process boundaries that differ from unfilled PA12. The aluminum phase is a combustible metal powder, but it is bound within a polymer matrix; the ignition sensitivity of the blended feedstock cannot be taken from either aluminum metal powder data or unfilled nylon data. Process hazard reviews should include dust explosion testing on the specific blend in the installed collection system under the relevant regional equipment directive such as 2014/34/EU. Extraction ducts, filters, and recoat area grounding must be maintained to prevent electrostatic discharge. No continuous metal powder cloud should be allowed to form during drum changes or sieve cleaning.

When tooling and visual prototypes require metal-like stiffness without high ductility

EOS Alumide is used in jigs, fixtures, and assembly aids where the higher modulus reduces flex during manual or robotic handling. The grey metallic appearance supports visual prototypes that must approximate die-cast aluminum parts, although the surface is polymer-bonded filler rather than a solid metal skin. Vacuum casting master patterns and short-run thermoforming tools have been produced from Alumide because the heat deflection temperature of 173 °C at 0.45 MPa under ISO 75-1/-2 allows brief low-load exposure in heated tooling environments. The material is not a direct substitute for machined aluminum in structural load paths; its tensile strength remains near 48 MPa, far below wrought aluminum alloys, and the low elongation at break of 4 % limits plastic deformation before failure. In applications where only appearance or moderate handling loads are required, the aluminum filler provides a functional stiffness-to-weight balance for a polymer part.

Post-processing of Alumide parts typically begins with depowdering and glass bead blasting to remove adhered particles and to brighten the metallic surface. The surface remains porous at the micro-scale, and published surface roughness data for Alumide-specific orientation sets are limited; general polymer-sintered parts are often reported with Ra values in the range of 5–10 µm before post-processing when measured by contact profilometry. Machining, tapping, and drilling are possible, but the brittle filler phase and porous interior can produce edge chipping and tool wear; carbide or diamond tooling is preferred over high-speed steel in production machining operations. Dimensional change from moisture absorption is lower than unfilled PA12 because the inert filler reduces the volume fraction of moisture-responsive matrix, but the effect is not zero and should be verified by conditioning parts under ISO 291 before precision assembly.

Dimensional tolerance retention in machined and post-sintered Alumide components.

The as-sintered part shrinks during cooling and must be compensated in the build file. Published shrinkage factors for EOS Alumide are not uniform across build axes; machine-specific scaling factors are provided in the material configuration file rather than as a single public number. Dimensional tolerance retention after post-processing is influenced by thermal history, part packing density, and wall thickness. For systematic production, manufacturers should validate a standard test artefact at different build positions and compare coordinate measuring machine results against ISO 2768-1 general tolerances or an agreed drawing note. The higher thermal conductivity of Alumide can reduce thermal gradients during cooling in thick sections compared with unfilled PA12, but it does not eliminate anisotropic shrinkage. Published data for this specific configuration are limited; therefore process capability studies on the target machine are required before quoting tolerance ranges for production parts.

In cyclical or snap-fit applications, the low elongation and sharp filler-matrix interfaces promote crack initiation at stress concentrations; the material is therefore unsuited to living-hinge or high-cycle fatigue functions without test data. For chemical exposure, the polyamide matrix provides resistance to oils and greases, but the aluminum phase can react with alkaline solutions and certain acids; compatibility testing is required under the specific concentration and temperature. The dispersed aluminum does not create a continuous electrical conduction path, and published data for surface or volume resistivity of this specific feedstock are limited. Operators must treat Alumide as a stiff, brittle, thermally conductive polymer composite rather than as a metallic material or as an unfilled PA12 processing equivalent.