27-06-2013, 01:10 PM
Microstructural characterization and mechanical properties in friction stir
welding of aluminum and titanium dissimilar alloys
Microstructural characterization.pdf (Size: 700.17 KB / Downloads: 40)
ABSTRACT
Al–Si alloy and pure titanium were lap joined using friction stir welding technology. Microstructure and
tensile properties of joints were examined. The maximum failure load of joints reached 62% of Al–Si alloy
base metal with the joints fractured at the interface. X-ray diffraction results showed that new phase of
TiAl3 formed at the interface. The microstructure evolution and the joining mechanism of aluminum–titanium
joints were systematically discussed.
Introduction
The joining of titanium alloy with aluminum alloy could have a
major application in the field of aerospace and automobile industry
where high strength and low weight are desirable [1,2]. However,
fusion welding joints between titanium and aluminum exhibit
inferior mechanical properties due to the formation of brittle intermetallic
phases in weld [1,3–5]. Other solid-state welding methods
for joining these two materials such as pressure welding [6], diffusion
bonding [7,8] and friction welding [2,9–11] processes have
been reported. Wilden et al. [8] reported diffusion bonding of commercially
pure Al and pure Ti. Selected mechanical testing results
of joints showed that diffusion bonding was a suitable process
for high strength applications. Fuji [9] studied the growth behavior
of an intermediate layer in a friction-welded joint between pure Ti
and pure Al. They concluded that the layer grew from the Al substrate
to the Ti substrate, and neither linear time dependence nor
parabolic time dependence could be used to describe the rate of
layer growth. Kim et al. [10] reported the dominant factors determining
the joint characteristics (strength, ductility, etc.) in friction
welds between Ti and Al.
Experimental details
The base materials are a 4 mm thick ADC12 cast aluminum alloy
sheet with a composition of Al-2.4–Cu-0.56–Zn-0.18–Mn-
0.81–Fe-0.17–Mg-11.8–Si (mass %) and a 2 mm thick commercially
available pure titanium sheet with a composition of Ti-0.045–Fe-
0.057–O-0.003–N-0.002–H-0.006–C (mass %). The sheet is cut
and machined into rectangular welding samples, which is
300 mm long and 100 mm wide. The samples are longitudinally
lap-welded using an FSW machine. The aluminum alloy sheet is
placed over the titanium sheet. The relative position of aluminum
alloy and titanium in transverse direction is shown in Fig. 1. The
welding parameters are at a rotation speed of 1500 rpm and at
welding speeds of 60 mm/min, 90 mm/min and 120 mm/min.
The upsetting force of the welding tool (made of WC–Co) used in
this experiment is 5.39 kN. The shoulder diameter and probe diameter
of the tool are 15 mm and 5 mm, respectively. The length of
the probe is 3.9 mm and the welding tilt angle is 3.
Conclusions
In summary, the following conclusions are reached. ADC12 Al
alloy and pure Ti can be successfully lap welded using friction stir
welding technology. The maximum failure load of lap joints can
reach 62% that of ADC12 Al alloy base metal. The transient phase
TiAl3 forms at the joining interface by Al–Ti diffusion reaction.
The formation of TiAl3 is strongly dependant on welding speeds
(heat inputs) during FSW and thus affects the mechanical properties
of joints. A preliminary investigation of friction stir lap joining
Al and Ti in the present materials indicates the feasibility of a defect-
free and considerable mechanical property lap joint.