Interfacial microstructure and mechanical properties of Ti−6Al−4V/Al7050 joints fabricated using the insert molding method
Int. J. Miner. Metall. Mater.
Interfacial microstructure and mechanical properties of Ti−6Al−4V/Al7050 joints fabricated using the insert molding method
Hong-xiang Li 2
Xin-yu Nie 2
Zan-bing He 2
Kang-ning Zhao 2
Qiang Du 1
Ji-shan Zhang 2
Lin-zhong Zhuang 0 2
0 IJmuiden Technology Centre, Tata Steel Research & Development , 1970 CA IJmuiden , The Netherlands
1 SINTEF Materials and Chemistry , Pb. 124 Blindern, NO-0314 Oslo , Norway
2 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing , Beijing 100083 , China
Ti−6Al−4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temperature during the first stage, and a good metallurgical bonding interface with a thickness of about 90 µm can be obtained at 750°C. X-ray diffraction, transmission electron microscopy, and thermodynamic analyses showed that the interface mainly contained intermetallic compound TiAl3 and Al matrix. The joints featured good mechanical properties, i.e., shear strength of 154 MPa, tensile strength of 215 MPa, and compressive strength of 283 MPa, which are superior to those of joints fabricated by other methods. Coherent boundaries between Al/TiAl3 and TiAl3/Ti were confirmed to contribute to outstanding interfacial mechanical properties and also explained constant fracture occurrence in the Al matrix. Follow-up studies should focus on improving mechanical properties of the Al matrix by deformation and heat treatment.
interfacial microstructure; interfacial bonding mechanism; mechanical properties; insert molding method; coherent boundaries; Ti/Al joints
1. Introduction
Given the low density, high specific strength, excellent
corrosion resistance, notable impact toughness, and
significant thermal stability, titanium alloys are widely used in
vehicle, aerospace, chemistry, and defense industries. However,
unavoidable shortcomings of titanium alloys, such as high
production cost, low thermal conductivity, and low shear
strength, constrain their widespread applications [
1
].
Aluminum alloys, as primary structural materials for
commercial and military applications, are known for their excellent
mechanical properties, easy to design, and mature
manufacturing and inspection techniques. However, these materials
also face other challenges, such as low hardness and wear
resistance, low tensile strength at high temperature, and high
linear expansion coefficient [
2
]. To overcome disadvantages
of Ti alloys and Al alloys and to utilize their respective
advantages, Ti/Al bimetallic joints have attracted more
attentions in recent years [
3−12
]. For these two alloys, significant
differences in physical properties, such as melting point
and heat conductivity, make conventional preparation
techniques unsuitable for fabricating Ti/Al joints. Novel
methods, such as accumulative roll-bonding [
3−5
], laser
welding–brazing [
6−7
], friction stir welding [
8−9
], powder
metallurgy [
10−11
], and explosive cladding [
12
], were
attempted. Despite these efforts, problems still exist with
these fabrication methods: (i) poor interfacial bonding
strength, (ii) complex processing procedures, and (iii)
limited product sizes for industrial application.
Recently, a study of Ti/Al−7Si−0.3Mg joints prepared by
a method of insert molding exhibited promising industrial
application prospects due to low production cost, low
energy consumption, simple production procedure, and high
interfacial bonding strength [
13−14
]. The basic principle of this
method is to immerse Ti insert into Al−7Si−0.3Mg melt at the
optimized temperature. As a result, good metallurgical bonding
can be attained by formation of an interfacial reaction layer.
Owing to the aforementioned outstanding advantages, the
authors also prepared Ti/Al and Ti−6Al−4V/Al bimetallic
joints using the same insert molding method [
15−16
].
Results showed that high interfacial shear strength can be
obtained by tuning holding time at a certain temperature and
optimizing the cooling method. Also, during shear
fracture, cracks can initiate and propagate in Al matrix near
the interface rather than in the interface reaction layer.
Summarizing the above progress regarding preparation
using the insert molding method, current studies mainly
focus on bonding of pure Al/pure Ti, pure Ti/Al alloys,
and pure Al/Ti alloys. So far, bonding of Ti alloys/Al
alloys obtained using the same insert molding method is not
performed though Ti-alloy/Al-alloy joints can exhibit more
extensive industrial application prospects. Though high
interfacial bonding strength can be attained, mechanism of
interfacial strengthening from the insert molding method
remains unknown. For these purposes, in this study, we
selected two representative alloys, i.e., Ti−6Al−4V and
AA7050 alloys, as two basic bonding metals and fabricated
corresp (...truncated)