Abstract
Electrical conducting wires of an aluminium matrix composite (AMC) were successfully produced by the novel production method of metal continuous screw extrusion (MCSE). The AMC
consisted of a matrix of commercially pure aluminium (AA1370) and Al2O3 particles as the
reinforcement material. The wires were produced with three varying parameters: the concentration of Al2O3 particles, the particle size of Al2O3 and the feeding rates of material (AA1370
granules and Al2O3 particles). The different particle sizes of Al2O3 particles were 0.5 µm, 5 µm
and 50 µm. The effect of Al2O3 particles on the electrical conductivity of the wires was investigated through resistance measurements and conductivity calculations. The microstructure
of the wires was investigated through light optical microscopy (LOM) and scanning electron
microscopy (SEM). Hardness measurements and tensile testing were performed to investigate
the mechanical strength of the wires. In addition, a particle analysis was carried out by image
processing of micrographs in the software ImageJ. The particle analysis yielded an estimation
of the Al2O3 concentration of the wires. A parallel that exhibited one of the highest values
for electrical conductivity obtained an electrical conductivity of (64.33 ± 0.26)%IACS with an
ultimate tensile strength of (64.44 ± 0.76) MPa. This parallel had the lowest concentration of
Al2O3 (2.72 wt% Al2O3) and a spiral particle distribution. The parallel with the highest Al2O3
concentration (7.47 wt% Al2O3) and a uniform particle distribution had the lowest electrical
conductivity with (56.54 ± 0.21)%IACS and an ultimate tensile strength of (99.45 ± 3.00) MPa.
It was established that the electrical conductivity of the composite was affected by the concentration and distribution of reinforcement particles. Increased amounts of reinforcement particles
led to decreased electrical conductivity of the screw extruded wires. In terms of particle distribution, wires with a spiral distribution of particles possessed areas with large grains and a
low presence of reinforcement particles, thus high electron mobility. In wires with a uniform
particle distribution, electrons more frequently encounter reinforcement particles, subsequently
reducing electron mobility and electrical conductivity. The effect of particle size on the electrical
conductivity was not possible to assess. The feeding rate of material was proven to strongly
influence the particle distribution and, therefore, affected the mechanical strength of the wires.
A uniform distribution of particles was obtained by a low feeding rate. This leads to strong wires
due to the fine-grained microstructure obtained by Zener pinning. A high feeding rate led to a
spiral particle distribution with a dense core of particles. Large grains were observed between
the spiral rings, as these areas were almost free of particles. Hence, a spiral particle distribution
facilitated a microstructure that contained large grains, leading to weaker wires. The properties
obtained for the screw extruded AA1370 wires containing Al2O3 were not considered sufficient
in order to act as competitive electrical conductors at present. However, screw extruded wires
with a spiral particle distribution creates new opportunities. Such wires could potentially serve
as overhead power lines. Regarding the feeding of reinforcement particles, it was found that
feeding of reinforcement particles through a screw feeder yielded an even flow and distribution
of material.