On the influence of powder particle size on single-track formation in laser powder bed fusion of AlSi10Mg alloy

TL;DR

This study investigates how powder particle size affects single-track formation in laser powder bed fusion of AlSi10Mg, revealing size-dependent melting behavior and energy density thresholds for stable track formation.

Contribution

It provides new insights into the influence of particle size on melting behavior and energy requirements in LPBF, supported by experimental and numerical analysis.

Findings

Particle size significantly affects the lack of fusion boundary.

Linear energy density ranges from 50 to 167 J/m for stable tracks.

Absorptivity varies with particle size and influences melting behavior.

Abstract

In this paper, we present the results of single-track experiments conducted for different fractions of standard AlSi10Mg powder, which were sieved to achieve varying mean size of the particles. We observed strong differences in the melting behaviour of fractions at relatively low levels of input energy in laser powder bed fusion (LPBF) process. Namely, the remarkable particle size effect arises for the position of lack of fusion boundary, i.e. for the range of process parameters where the laser power becomes sufficient for complete through-thickness melting of the powder layer at given laser scanning speed. We established that this boundary corresponds to an approximately constant linear energy density at low levels of Peclet number (Pe < 2), while the constant enthalpy density defines this boundary at the higher levels (Pe > 2). Specifically, when the mean particle size ranges from 28 to 64 microns, the required linear energy density for stable track formation ranges from 50 to 167 J/m and the nominal enthalpy density ranges from 4.4 to 15 J/mm^3. Based on the scaling law analysis and numerical simulations, we show that observed phenomena can be attributed to the change of absorptivity of powder layer, which depends on particle size and packing density. Also, we show that the values of absorptivity identified based on the analysis of position of lack of fusion boundary (0.13-0.38 for powder size 64-28 microns) correlate well with those found from the analysis of melt pool width in the formed single-tracks.