Combined effect of inoculation and magnetic arc oscillation on microstructure and tensile behaviour of type 2090 Al–Li alloy weld fusion zones

Solidification and liquation cracking issues in welding

Abstract: Solidification cracking can occur in the fusion zone during the solidification of the weld metal Liquation cracking, on the other hand, can occur in the partially melted zone during the solidification of the liquated material These two types of cracking are reviewed in this article, including the factors that affect cracking and the remedies

Effect of beam oscillating pattern on weld characterization of laser welding of AA6061-T6 aluminum alloy

Abstract: Laser oscillating welding was employed to join 4 mm-thick AA6061-T6 aluminum alloy in butt configuration. Three beam oscillating patterns that are transversal, longitudinal and circular were studied. The beam oscillation improved the weld morphologies and promoted the formation of equiaxed grain within the fusion zone due to stirring effect. The circular oscillation obtained the soundest weld, the finest grain and the most amount of equiaxed grains within the weld. The beam oscillation almost had no effect on the tensile strength of the weld, but increased the ductility obviously. The strain of circularly oscillating weld was up to 8%, 38% higher than the weld without beam oscillation. The ductility improvement was attributed to the decrease of weld morphological defects and the increase of equiaxed grains. Besides, the improving mechanisms of weld characterization were discussed by the beam oscillating effect on the behaviors of laser keyhole and melt flow.

Grain refining by ultrasonic stirring of the weld pool

Abstract: Grain refining can improve the mechanical properties and solidification-cracking resistance of the weld. Ultrasonic grain refining was conducted by dipping an ultrasonic probe in the weld pool to stir it at a distance behind the arc. This new approach produced effective grain refining in arc welds of Mg alloys AZ31 Mg and AZ91 Mg. Grain refining increased when the probe was positioned farther behind the arc. This suggests the initial crystallites or dendrite fragments generated by ultrasound in a cooler melt farther behind the arc were better able to survive. This also suggests dendrite fragmentation was more likely to occur because the probe was closer to the mushy zone. However, a probe too far behind the arc ended up being inside the mushy zone and grain refining, though highly effective, was restricted to only near the weld centerline. At the same probe position, grain refining increased with increasing ultrasound amplitude. Grains were significantly finer in AZ91 Mg welds than AZ31 Mg welds. This suggests grain refining increased with increasing constitutional supercooling caused by the higher solute content of AZ91 Mg than AZ31 Mg.

Microstructure and mechanical properties of Sc modified Al–Cu alloy (AA2219) electron beam welds

Abstract: In this paper, the formability of YAG and diode laser welded blanks of a dual phase (DP) steel with banded martensite was investigated by using limiting dome height (LDH) testing method. One high strength low alloy (HSLA) steel with equiaxed ferrite matrix was included for comparison. Both steels had a ferrite matrix and dispersed secondary phase, namely martensite and carbide. The failure mode and dome height at fracture were examined on both parent metals and welded blanks. It was found that the failure pattern of DP parent metal was determined by its rolling direction. With increasing plastic strain, voids initiated along interfaces between ferrite/martensite due to decohesion between two phases and propagated preferentially along the interface. For DP welded blanks, dome test failures occurred within the softened zone in the heat affected zone (HAZ) regardless of the orientation between weld and rolling direction. Voids formed at the interfaces between ferrite and tempered martensite. The presence of the softened HAZ zone led to dramatic LDH decrease compared to the parent metal. The diode laser welded blanks had a lower dome height than that of YAG laser welded blanks due to their more severe HAZ softening. In comparison, HSLA parent metal and welded blanks exhibited almost the same LDH values and showed insensitivity to welding process. The failure of HSLA welded blanks initiated from the weld and propagated perpendicular to the unaffected base metal.

Effects of electron beam oscillation techniques on solidification behaviour and stress rupture properties of Inconel 718 welds

Abstract: Effects of electron beam oscillation techniques (sinusoidal, square, triangular, ramp, circle and elliptical) in controlling Nb segregation, Laves formation and stress rupture behaviour of Inconel 718 electron beam welds are studied. Effects of various post-weld heat treatments on stress rupture behaviour are compared. Elliptical beam oscillation technique resulted in less Nb segregation and discontinuous and fine Laves in the interdendritic regions compared with other welds and unoscillated beam weld. Response to aging was better for welds made with elliptical oscillated beam compared with welds made with unoscillated beam. Oscillated beam welds exhibited longer rupture life than unoscillated beam welds in both solution treated and aged and directly aged conditions.

Weld microstructure refinement in a 1441 grade aluminium-lithium alloy

Abstract: Clad 2 mm thick sheets of Russian 1441 grade Al-Li alloys were welded using a gas tungsten arc welding process (GTAW). Comparisons were made between the weld beads obtained under (i) continuous current (CC), (ii) pulsed current (PC), and (iii) arc oscillation (AO) conditions for their macro- and microstructural details. In the case of CC GTAW, sound welds could be produced only under a narrow range of welding parameters. Centre line cracks, which occurred in CC GTAW welds under certain conditions, were halted by switching to PC or AO conditions while the welding was in progress. Microstructural refinement was significant in the case of PC and AO GTA welding.

Grain refinement in magnetically stirred GTA welds of aluminum alloys

Abstract: The mechanisms of grain refinement have been examined for magnetically stirred gas tungsten arc (GTA) welds completely penetrating thin sheets of several aluminum alloys. Grain refinement in unstirred welds may be brought about by adding sufficient titanium to produce heterogeneous nucleation by Ti-rich particles. In some alloys magnetic stirring is shown to extend the range of welding conditions which produce a partially equiaxed structure, and to widen the equiaxed fraction of partially equiaxed welds. This is attributed to magnetic stirring lowering the temperature gradient, allowing nucleation and growth of Al-rich grains further ahead of the columnar interface growing in from the fusion boundaries. In alloys with low Ti levels, magnetic stirring may cause refinement by sweeping grains from the partially molten zone ahead of the advancing solidification interface. This mechanism requires that the partially molten zone be sufficiently wide, and that the grain size in this zone remain small.

Grain structure and solidification cracking in oscillated arc welds of 5052 aluminum alloy

Abstract: The effect of arc oscillation on grain structure and solidification cracking in GTA welds of 5052 aluminum alloy was investigated using a four-pole magnetic arc oscillator and a modified fish-bone crack test. Two different mechanisms of crack reduction were identified: one in the low frequency range of arc oscillation and the other in the high frequency range. The former was the alteration of the orientation of columnar grains, while the latter was grain refining. Neither mechanism was operative in the intermediate frequency range and solidification cracking was severe, especially when the amplitude of arc oscillation was small. Alteration of grain orientation was obtained in welds made with transverse and circular arc oscillations, but not longitudinal arc oscillation. Grain refining, on the other hand, was achieved in welds made with all three types of arc oscillation patterns. The differences between the response of alloy 5052 to arc oscillation and that of alloy 2014 observed previously were discussed.

The weldability of lithium-containing aluminium alloys

Abstract: Lithium-containing aluminium alloys have reduced density and increased elastic modulus compared with conventional aluminium alloys. Many such alloys are currently under development for aircraft applications, which usually involve mechanical fastening. Consequently, the weldability of lithium-containing aluminium alloys is currently receiving relatively little attention. The weldability of lithium-containing aluminium alloys is reviewed. The vast majority of the welding studies performed have been on the Soviet Al-5 wt% Mg-2 wt% Li alloy, 01420. Alloy 01420 and other lithium-containing aluminium alloys are indeed fusion weldable, and weldments having high joint efficiencies have been made.

Recent developments in the weldability of lithium-containing aluminium alloys

Abstract: The weldability of aluminium-lithium alloys is reviewed with emphasis on alloys that are being commercialized: 2090, 8090 and Weldalite™ 049. These alloys are weldable, although hotcracking susceptibility has been reported for 2090 and 8090 when welded with certain conventional filler alloys. Mechanical property data from weldments made by several techniques are emphasized. Weld-zone porosity problems, discussed at length in a 1985 review in this journal, have largely been controlled by proper weld pretreatment and gas shielding. Interest in the weldability of aluminium-lithium alloys has taken on increased significance because of their potential to reduce the weight of space launch systems, whose fabrication most often involves welding.