With the growing demand for vehicle weight reduction and the increased application of multimaterial design, it is imperative to address the challenges of welding dissimilar light alloys. This paper presents a review on laser welding of Al/Mg, Al/Ti, and Mg/Ti alloys, with focus on the techniques used to suppress the formation of brittle intermetallic compounds (IMCs) and improve joining mechanism. For Al/Mg joints, studies have shown that the use of structural adhesives, the use of interlayers such as Ce, Ni, Ti, and Fe foils and Zn-Al filler metals, and hybrid adhesive-interlayers could suppress the formation of brittle IMCs and improve joint strength. The formation of brittle IMCs during laser welding of Al/Ti alloys could be minimized by offsetting the laser beam at an appropriate distance towards either the Al or Ti alloy, the use of split-beam laser with appropriate joint design, the use of high welding speed, improving the laser energy distribution, and the use of V-groove with Al-Si filler metals. For Mg/Ti alloys, offsetting the laser beam at an appropriate distance towards the Mg alloy, the use of AZ series Mg alloy-based filler wires, and coating the Ti alloy with Ni were found to facilitate the joint formation and improve the joint strength.

Challenges and advances in laser welding of dissimilar light alloys: Al/Mg, Al/Ti, and Mg/Ti alloys

Disk laser weld brazing of dissimilar metals was carried out. Aluminum alloy 5083 and commercially pure titanium Grade 2 with the thickness of 2.0 mm were used as experimental materials. Butt weld brazed joints were produced under different welding parameters. The 5087 aluminum alloy filler wire with a diameter of 1.2 mm was used for joining dissimilar metals. The elimination of weld metal cracking was attained by offsetting the laser beam. When the offset was 0 mm, the intermixing of both metals was too high, thus producing higher amount of intermetallic compounds (IMCs). Higher amount of IMCs resulted in poorer mechanical properties of produced joints. Grain refinement in the fusion zone occurred especially due to the high cooling rates during laser beam joining. Reactions at the interface varied in the dependence of its location. Continuous thin IMC layer was observed directly at the titanium–weld metal interface. Microhardness of an IMC island in the weld metal reached up to 452.2 HV0.1. The XRD analysis confirmed the presence of tetragonal Al3Ti intermetallic compound. The highest tensile strength was recorded in the case when the laser beam offset of 300 μm from the joint centerline toward aluminum alloy was utilized.

Disk Laser Weld Brazing of AW5083 Aluminum Alloy with Titanium Grade 2

Process of welding-brazing and interface analysis of lap joint Ti-6Al-4V and aluminum by plasma arc welding

An investigation was carried out to study the ability to carry out dissimilar welding between
Ti-6Al-4Valloy and commercially pure vanadium alloy. Electron beam melting machine
(EBM) was adopted for EBW for the dissimilar welding process using an Arcam S12 system.
A promising beam setting was generated using the design of experiment (DoE). DoE
normalised parameters and discrete parameters were suggested to find the best beam welding
setting. Using different normalising approaches helped to establish a full penetration weld
with acceptable characteristics: weld root and weld undercut when set II was applied.
Powder technology means and Spark Plasma Sintering was employed to design a filler metal
to be used in dissimilar welding. Based on the microstructures and mechanical analysis, the
designed filler metals Ti/V, Ti/V2 and Ti/V3 were selected as the designated interlayers to
be prefixed in the joints between titanium base metal (Ti-BM) and vanadium base metal (VBM) in the pre-welding process. Dissimilar welding was performed based on the best beam
parameters obtained from the beam optimisation methods. A successful full penetration weld
was achieved between Ti-6Al-4V and CP-V alloys directly, without filler metals, which
offered a tensile strength reaching to 282 MPa. When the 5 mm thin interlayer was added to
the welding zone, the welds W1, W2 and W3 achieved strength close to that of the non-filler
weld AW0. The hardness measurements for the welding zone (WZ) revealed increments in
hardness values when the V content was increased in the WZ, reaching a maximum value of
345 HV1 for the WZ of weld type W2. The W2 weld sample, also, showed superior strength,
reaching to ~270 MPa. The presence of solid-solution phase βTi-V reduced the hardness
values from 375±5 HV1 in the case of the keyhole titanium weldtracks to about 354 HV1 in
the WZ of the Ti-V dissimilar joint. Hardness measurements showed that the highest and
lowest hardness values were in the titanium heat affected zone (Ti-HAZ) and vanadium heat
affected zone (V-HAZ), respectively. Additionally, tensile tests confirmed that material
failure occurred in the base metal with lower mechanical properties, i.e. vanadium, and not
in the weld joint. Necking condition was observed in the V-HAZ in all the tensile samples
with and without the filler metals, and as the failure took place outside the WZ this suggests
that the attempt to carry out dissimilar welding between Ti-6Al-4V alloy and CP-V alloy
was successful.

Joining Lightweight Dissimilar Alloys by Using Electron Beam Welding

The welding of titanium and aluminum is difficult due to differences in their material properties and the formation of intermetallic compounds (IMCs) which can weaken the weld. A new process, Friction Stir Extrusion (FSE), has been used to join dissimilar materials by using Friction Stir Processing to extrude a top sheet of material into a pre-made, concave groove in the bottom sheet of material. FSE has been used to create a strong, mechanically interlocking joint between aluminum 6061 and steel that eliminates IMCs. However, FSE hasn’t been applied to any other material combinations. This current research applies the FSE process to join aluminum 2024-T4 to commercially pure titanium. The process was optimized by adjusting the RPM, traverse rate, and groove geometry. The Al–Ti joints are evaluated based on shear strength and ultimate tensile strength. The groove geometry proved to be the most important parameter as different geometries can enhance the strength by mechanical means and by optimizing the volume and shape of the material extruded. Successful joints were created by the FSE process and can be used as a viable alternative for joining aluminum to titanium.

Joining Aerospace Aluminum 2024-T4 to Titanium by Friction Stir Extrusion

Titanium was successfully welded to Aluminum using laser welding. Laser welding parameters ranges combinations were experimentally determined using Taguchi approach with the objective of producing welded joint with acceptable welding profile and maximizing the tensile shear strength. Tensile shear strength of dissimilar Al/Ti was evaluated as a response function of the selected laser welding parameters and statistical model was developed to describe it. The result indicates that the developed model can predict the responses satisfactorily. Tensile strength of the joints was found to be same as Al base metal. Furthermore the microstructure and microhardness of the joint have been studied.

http://iopscience.iop.org/article/10.1088/1742-6596/181/1/012033/pdf

F A Elshukri

Papers

Modeling and optimization of tensile shear strength of Titanium/Aluminum dissimilar welded component