Citation: Trautmann, M.; Ahmad, H.;
Wagner, G. Influencing the Size and
Shape of High-Energy Ball Milled
Particle Reinforced Aluminum Alloy
Powder. Materials 2022, 15, 3022.
https://doi.org/10.3390/ma15093022
Academic Editors: Ludwig Cardon
and Clemens Holzer
Received: 16 March 2022
Accepted: 18 April 2022
Published: 21 April 2022
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Article
Influencing the Size and Shape of High-Energy Ball Milled
Particle Reinforced Aluminum Alloy Powder
Maik Trautmann * , Husam Ahmad and Guntram Wagner
Professorship of Composites and Material Compounds, Chemnitz University of Technology,
09107 Chemnitz, Germany
; husam.ahmad@mb.tu-chemnitz.de (H.A.); guntram.wagner@mb.tu-chemnitz.de (G.W.)
* Correspondence: maik.trautmann@mb.tu-chemnitz.de
Abstract:
High-energy ball milling represents an efficient process for producing composite powders
consisting of ceramic particles dispersed in a metallic matrix. However, collision events, plastic
deformations, and cold welding during the milling lead to a flake or block-like shape of the resulting
composite powders. Further consolidation of such irregularly shaped powders by powder bed-based
additive manufacturing technologies can be challenging because of their low flowability and low
bulk density. In this work, different approaches, including milling process parameters (speed, process
control agent atmosphere) and post-treatments (mechanical and thermal), are investigated on their
suitability to influence the particle shape, especially concerning the roundness of the composite
powders consisting of the aluminum alloy AlSi10Mg with 5 vol% SiC and Al
2
O
3
reinforcement. It
is found that milling with menthol as a process control agent leads to the finest composite powder
compared to other milling parameters, with the lowest particle roundness of 0.39 (initial powders
0.84). No success in rounding the milled composite powder could be achieved through mechanical
post-treatment in a planetary ball mill. On the other side, the thermal spraying of, e.g., SiC reinforced
AlSi10Mg powder resulted in a 77–82% relative roundness. A remarkable change in the microstructure
and the shape of the composite powders could also be observed after heat treatment in tube furnaces at
a temperature above the melting point of AlSi10Mg. The best result in terms of improved roundness
(relative to around 85%) was obtained for Al
2
O
3
reinforced at 600
◦
C. A further increase of the
temperature to 700
◦
C resulted in a moderate coarsening of powders with Al
2
O
3
and extensive
sintering of powders with SiC, presumably due to a different distribution inside the matrix.
Keywords: metal matrix composites; spheroidization; composite powder; additive manufacturing
1. Introduction
Aluminum and aluminum alloys belonging to a material category have widespread
applications in many civil sectors, automobile, and aerospace industries, among others, not
only due to their low density and high specific strength, good machinability, and relatively
low cost. Further improving and adjusting of the properties of aluminum alloys can be
achieved by incorporating an additional reinforcing hard phase into the microstructure.
With respect to low-cost production, particle reinforcement represents a simple and effective
way to improve the properties of aluminum alloys. This is because of their ability to be
processed with traditional and established technologies used for monolithic materials.
Thus, particle reinforced aluminum matrix composites (AMC) are produced by powder
metallurgy methods and melt metallurgy methods [1,2].
One of the main strengths of the powder metallurgy route is the possibility of dispers-
ing nano scaled ceramic particles within the metallic matrix through—for
example—high
-
energy ball milling (HEBM), also known as mechanical alloying (MA). The resulting
composite powder is then compacted by means of one of the conventional press techniques
such as axial pressing or isostatic pressing. Using this approach, up to 15 vol% SiC parti-
cle fraction could be homogeneously distributed in the aluminum alloy AA2017, which
Materials 2022, 15, 3022. https://doi.org/10.3390/ma15093022 https://www.mdpi.com/journal/materials
