Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core–shell-structured Ti/Al3Ti
Int. J. Miner. Metall. Mater.
Microstructure and mechanical properties of a hot-extruded Al-based composite reinforced with core-shell-structured Ti/Al3Ti
Li Zhang 0 1
Bao-lin Wu 0 1
Yu-lin Liu 0 1
0 Liaoning Key Laboratory of Aviation Light Alloy and Processing Technology, Shenyang Aerospace University , Shenyang 110136 , China
1 School of Materials Science and Engineering, Shenyang Aerospace University , Shenyang 110136 , China
An Al-based composite reinforced with core-shell-structured Ti/Al3Ti was fabricated through a powder metallurgy route followed by hot extrusion and was found to exhibit promising mechanical properties. The ultimate tensile strength and elongation of the composite sintered at 620°C for 5 h and extruded at a mass ratio of 12.75:1 reached 304 MPa and 14%, respectively, and its compressive deformation reached 60%. The promising mechanical properties are due to the core-shell-structured reinforcement, which is mainly composed of Al3Ti and Ti and is bonded strongly with the Al matrix, and to the reduced crack sensitivity of Al3Ti. The refined grains after hot extrusion also contribute to the mechanical properties of this composite. The mechanical properties might be further improved through regulating the relative thickness of Al-Ti intermetallics and Ti metal layers by adjusting the sintering time and the subsequent extrusion process.
microstructure; aluminum-based composites; Ti/Al3Ti; reinforcements; mechanical properties
1. Introduction
Particulate-reinforced aluminum matrix composites
(PRAMCs) have potential applications in the aviation,
aerospace, and automotive fields because of their outstanding
mechanical properties, which include high specific strength,
high specific modulus, high hardness, and low thermal
expansion [
1−2
]. PRAMCs with ceramic particles such as SiC,
Al2O3, and B4C as the reinforcement material have been
well developed. However, brittle layers always form
between particles and the Al matrix because of chemical
reactions that usually result in weakening of the interfacial
bonding [3]. Reducing the harmful effect of this brittleness
on the properties of such composites is an important
research topic.
If a casting method is used, the formation of brittle layers
should be controlled through reducing chemical reactions
between the particulates and the liquid. As a convenient
method to fabricate Al-based composites, powder
metallurgy is considered a superior method because it enables easier
control of the interfacial layer. It also features other
advantages such as easy adjustment of the ingredients, the ability
to produce homogeneous microstructures and clean
interfaces, and convenient near-net shaping [
4−6
].
To avoid the aforementioned brittleness, particulates with
metal characteristics can be used as reinforcement; such
particulates will result in decreased brittleness of the bonding
layer between particulates and the Al matrix. Recently,
metallic particulates such as Ni, Fe, and Ti have been added to Al
matrixes to form NixAly, Al5Fe2, and Al3Ti as intermetallic
reinforcements in PRAMCs through in situ reaction [
7−10
].
The results show that the mechanical properties of the
composites were improved. Because Al3Ti exhibits a low
density, a high modulus, good wear resistance, excellent specific
strength, and a coefficient of thermal expansion similar to
that of the Al matrix, it has attracted attention as a potential
reinforcement material for Al-based composites [
11−12
].
Al3Ti is attractive as a component for PRAMCs used in
aviation, aerospace, and automotive applications. However, the
literature contains few detailed studies of the microstructure
development of Al3Ti-containing PRAMCs during sintering
and the effect of Al3Ti on the mechanical properties of the
resultant composites.
In this work, an Al-based composite was prepared
through powder metallurgy and subsequent extrusion. The
metallic powder Ti was chosen as the original particles to
form the core–shell-structured Al3Ti reinforcement phase.
The microstructure development and mechanical properties
were then investigated. The mechanism of the formation of
the core–shell structure is discussed. The results serve to
improve the mechanical performance of Al-based
composites.
2. Experimental
Gas-atomized pure Ti powder with particle diameters
ranging from 30 to 50 μm and pure Al powder with an
average particle diameter of (2 ± 0.5) μm were chosen as the
starting materials. The micrographic morphologies of the
two powders were observed under a Zeiss Sigma
field-emission scanning electron microscope, as shown in
Figs. 1(a) and 1(b). They were mixed with a mass ratio of
30:70 (the volume fraction of Ti particles was
approximately 20%) in a planetary-type grinding machine. To obtain
different interfacial bonding layers, the fully mixed powders
were sintered at 600, 620, or 640°C under a reduced
pressure of 4.0 × 10−3 Pa or less or under an elevated pressure of
150 MPa for 5 h. The sintering (...truncated)