Aluminium alloy welding by CO2 laser using filler wire ‐AIN formation and aluminium alloy weldability

Based on literature sources and the author's own research, this article presents the current state of knowledge about composite coatings created by means of the plasma transfer method. The general characteristics of composite coatings and their strengthening mechanisms have been described. Methods of creating composite coatings by means of the plasma transfer method have also been discussed.     

Homogenisation of chemical composition and microstructure in laser filler wire welding of AA 6009 aluminium alloy by in situ electric current stirring

Owing to the rapid cooling rates, the deposited and base metals could be mixed incompletely during laser welding of Al alloys in most cases. The objective of this research is to explore a possible method to promote the mixing of materials inside the molten pool by making use of the magnetofluid dynamic effect of electric current. Full penetration CO₂ laser welding of 3?mm thick alloy 6009 sheets was performed with an external electric current simultaneously into the weld pool via a filler wire. It is found that the deposited metal is mainly concentrated on the upper part of the weld fusion zone, and the weld zone microstructure is non-uniform without the electric current addition. With the application of an electric current, the weld fusion zone geometry is reshaped, and the chemical composition and microstructure of the weld metal are homogenised. The mechanism is found to be electromagnetic force stirring of the molten pool.     

Prevention of porosity by oxygen addition in fibre laser and fibre laser–GMA hybrid welding

Prevention of porosity in partial penetration fibre laser and fibre laser–gas metal arc hybrid welding is investigated. It is found that modulation of laser power prevents porosity formation in fibre laser welding, but that this method is not effective in hybrid welding. However, the addition of a small amount of oxygen to the molten pool can prevent porosity formation in both fibre laser and hybrid welding. This is attributed to stabilisation of the keyhole. During welding, oxygen reacts with dissolved carbon to form carbon monoxide (CO) in the keyhole. The CO partial pressure in the keyhole prevents the intense interaction between laser beam and molten metal, thus stabilising the keyhole. The role of CO formation is confirmed by the enhancement of porosity suppression with increased carbon content of the base metal.     

Laser welding of high-strength aluminium–lithium alloys with a filler wire

The possibilities of using laser welding with a filler wire for joining sheet materials made of V-1469 and V-1461 high-strength aluminium–lithium alloys are investigated. The optimum conditions of placing the filler wire in relation to the laser beam in the weld pool are determined. The optimum welding parameters resulting in the high-quality formation of the welded joint with equal sagging and excess metal and the absence of porosity and cracks are also determined. The mechanical properties of welded joints are outlined and the microstructure of the welded joint is investigated. The corrosion resistance of the produced welded joints is studied.     

A preliminary study on filler metals for vacuum brazing of Al/Ti

In this paper,nine new filler metals contained Sn and Ga based on Al-11.5Si have been designed for vacuum brazing of Al/Ti.It is found that the addition of Sn and Ga can lower the solidus of filler metal,change the structure of intermetallic compound formed in the joint during brazing,and enhance the strength of joint.But the detail mechanism need further research.     

CO2 laser welding–brazing characteristics of dissimilar metals AZ31B Mg alloy to Zn coated dual phase steel with Mg based filler

The influence of process variables including heating mode, flux, laser beam offset, and travel speed on the weld bead geometry and joint strength was investigated during laser welding–brazing (LWB) of AZ31B Mg alloy to Zn coated steel. The wettability of molten filler metal on steel surface was studied via a Charge-coupled Device (CCD) camera. The reaction layers along the interface were characterized and the failure mechanism was identified. Dual beam processing was found to preheat the steel substrate and promote the wettability of molten filler metal on the steel surface, thereby improving the corresponding joint strength. Utilizing a flux was found to produce a similar effect on molten filler metal. The optimized range of laser offset was found to be between 0.5 and 1.0 mm toward the steel side of the joint. These optimized parameters led to a maximum joint strength of 228 N/mm. The joint strength was however found to decrease with increasing travel speed. Cracking was identified with travel speeds greater than 1 m/min. Microstructural characterization showed that heterogeneous interfacial reaction layers were produced from the seam head to the seam root of the joint. The reaction layer thickness varied within a certain range when applying different process parameters, suggesting the growth of interfacial layer was not essentially related to the heat input. The primary failure mode of the lap specimens was interfacial fracture. Cracks propagated along the Mg–Zn reaction layer and steel interface. Original Fe–Al phase formed during the hot-dip galvanization process hindered the metallurgical bonding of Mg–Zn reaction layer and steel substrate, which was attributed to interfacial type failure.     

Stitch welding of Ti–6Al–4V titanium alloy by fiber laser

Stitch welding of plate covered skeleton structure of Ti–6Al–4V titanium alloys has a variety of applications in aerospace vehicle manufacture. The laser stitch welding of Ti–6Al–4V titanium alloys was carried out by a 4 kW ROFIN fiber laser. Influences of laser welding parameters on the macroscopic geometry, porosity, microstructure and mechanical properties of the stitch welded seams were investigated by digital microscope, optical microscope, scanning electron microscope and universal tensile testing machine. The results showed that the three-pipe nozzle with gas flow rate larger than 5 L/min could avoid oxidization, presenting better shielding effect in comparison with the single-pipe nozzle. Porosity formation could be suppressed with the gap between plate and skeleton less than 0.1 mm, while the existing porosity can be reduced with remelting. The maximum shear strength of stitch welding joint with minimal porosity was obtained by employing laser power of 1700 W, welding speed of 1.5 m/min and defocusing distance of +8 mm.     

Effect of filler wire on the joint properties of AZ31 magnesium alloys using CO2 laser welding

Laser welding with filler wire of AZ31 magnesium alloys is investigated using a CO2 laser experimental system. The effect of three different filler wires on the joint properties is researched. The results show that the weld appearance can be effectively improved when using laser welding with filler wire. The microhardness and tensile strength of joints are almost the same us those of the base metal when ER AZ31 or ER AZ61 wire is adopted. However, when the filler wire of ER 5356 aluminum alloy is used, the mechanical properties of flints become worse. For ER AZ31 and ER AZ61 filler wires, the microstructure of weld zone slws small dendrite grains. In comparison, for ER 5356 filler wire, the weld shows a structure of snowy dendrites and many intermetallic compounds and eutectic phases distribute in the dendrites. These intermetallic constituents with low melting point increase the tendency of hot crack and result in fiagile joint properties. Therefore, ER AZ31 and ER AZ61 wire are more suitable filler material than ER 5356 for CO2 laser welding of AZ31 magnesium alloys.     

A study on the porosity of CO2 laser welding of titanium alloy

0IntroductionTitanium alloys are increasingly applied in aeronauticindustry because of its higher strength to weight ratio thansteel and superior fatigue performance to aluminum alloy.At the same time there are many newtitanium-based alloysoccurring,such as Ti3Al-Nb titanium aluminide[1].Weldsof titanium alloy are prone to porosity,presenting a poten-tial problem for many application requiring sealing,corro-sion and fatigue resistance and good fracture toughness.Many studies have demonstrate…     

Resistance flash butt welding of pressed profiles of 1545KM alloy (Al–Mg–Sc)

Investigations were carried out into the special features of resistance flash butt welding of ring-shaped components of frames of 1545KM alloy, the welding conditions were determined, and the structure, mechanical properties, and service properties of the welded joints were examined in the composition of the fuel tank of a rocket carrier.     

Arc spectral processing technique with its application to wire feed monitoring in Al–Mg alloy pulsed gas tungsten arc welding

The principal component analysis (PCA) is applied for three purposes: spectral line identification, redundancy removal and spectral characteristic signals extraction. The spectral information is classified as the first and the second principal components, associated with Ar I lines and metal lines, respectively. With the mean value method, pulse interference resulted from the pulse current is eliminated from the spectral signals. The relationships among these extracted signals and the defects resulted from wire feed are discussed and the results show that the second principal component is closely related to these defects while the first principal component has relationship with the arc states. To test validity of the extracted signals, a back-propagation neural network is designed and appropriately trained with “Early Stopping” technique to detect these defects automatically.     

CO2 laser welding of 5A06 aluminum alloy plates with different thicknesses

CO2 laser beam welding of aluminum alloys with different thicknesses was carded out. The influences of laser power and travel speed on the weld width were analyzed. The mechanical characteristics of tailor-welded blanks （TWB） with unequal thickness were evaluated using tensile tests, and the fracture appearance was inspected after tensile tests. The microstructure of welded joints was analyzed by SEM. The results indicate that this alloy can be laser welded with full penetration. All the tensile specimens fracture on the base metal, far from the weld in the transverse direction. The tensile strength and yield strength of TWB are 89% and 91.2% compared with the base metal. The percentage of the thinner plate in the specimen has an important effect on the transverse elongation. The transverse elongation of TWB approaches that of the base metal when the thinner plate has a large percentage in TWB specimen. The weld microstructure shows extra-fine grains. Dendrite exists around weld fusion line and the equiaxed grains in the weld.     

A study on laser cleaning and pulsed gas tungsten arc welding of Ti–3Al–2.5V alloy tubes

An alternate cleaning process to chemical process of Ti–3Al–2.5V tube surface by a pulsed fiber laser and welding of the laser-cleaned tubes with end fittings by Pulsed Gas Tungsten Arc Welding (GTAW-P) technique is reported in this paper. Results on surface morphology, hardness, chemical composition, metallography and X-ray radiography are presented for laser assisted cleaning and welding of Ti–3Al–2.5V alloy tubes. Welding of laser-cleaned samples show excellent weld quality.     

Microstructure and corrosion behaviour of alloy 690–SUS 304L butt joints formed by electron beam welding

Abstract

This study investigates the microstructure and corrosion behaviour of alloy 690–SUS 304L stainless steel dissimilar weldments formed by electron beam welding (EBW). Slow strain rate tensile tests (SSRTs) are performed in air and in a 0·01M Na₂S₂O₃ + 1 wt-%NaCl corrosive environment. The microstructure, mechanical properties and corrosion behaviour of the weldments are analysed. Experimental results of this study reveal that the precipitation of chromium carbide is suppressed owing to the effect of rapid solidification of EBW in fusion zone (FZ). In addition, there is no chromium depletion found at the grain boundary at all. The interdendritic region of the FZ contains fine precipitates, which are a mixture of Ti rich phases with a rectangular shape and Cr rich phases with an oval shape. Fewer interdendritic phases are formed in the root than in the cap owing to the higher cooling rate in the root region of the weldment. Fracture tests indicate that all the specimens ruptured in the FZ by SSRTs preformed either in air and or in a corrosive environment. The tensile strength and total tensile elongation of the specimen deformed in the 0·01M Na₂S₂O₃ + 1 wt-%NaCl corrosive environment are lower than those of the specimen deformed in air. Fractographic investigations revealed that the fracture mode, in good accordance with mechanical behaviour and performance, transits from a ductile dimple rupture in the specimens tested in air to a mixed rupture of dimples and corrosion formation on fractured surface which obviously assisted the cracking in the specimens tested in the corrosive environment.     

Wire-array-applied ultrafine tungsten wire coated with Al–Mg alloy layer via electron beam evaporation

Al–Mg alloy coatings were deposited onto superfine tungsten wire substrates via electron beam deposition at electronic beam currents ranging from 80 to 120?mA. The effects of electronic beam currents and baking process on the surface characteristics of the aluminium–magnesium alloy coatings were investigated using scanning electron microscopy. Energy-dispersive X-ray was also used to investigate the composition of the coatings according to the chemical components of the source materials. X-ray diffraction results suggested that the Al–Mg alloy coatings consisted of an Al₁₂Mg₁₇ intermetallic compound and pure aluminium phase. Electrochemical measurements determined the corrosion protection performance of the aluminium–magnesium alloy coatings with different magnesium contents. Specimen tensile properties were related to electron beams and surface roughness. The anti-corrosion performance of the coatings was increased with magnesium content.     

Characteristics of TIG arc-assisted laser welding–brazing joint of aluminum to galvanized steel with preset filler powder

Tungsten inert gas(TIG) arc-assisted laser welding–brazing was used for the butt joining of 5A06 aluminum alloy to the galvanized steel by preset filler powder without groove. The spreading behavior of liquid metal on the back of the galvanized steel at different assisted welding currents was also investigated. The results show that the assisted TIG arc optimizes the interface reaction temperature, enhances the wettability of liquid metal on the steel side, and forms a sound butt joint at an appropriate welding current. A non-uniform intermetallic compound is formed at the interfacial layer, which is composed of Fe2Al5 close to the steel substrate and Fe4Al13 close to the solidified aluminum. The superior tensile strength of joint is indicated when the welding current ranges from 13 to 16 A. The average tensile strength can reach 151 MPa at the welding current of 16 A, and the corresponding fracture belongs to the ductile and brittle hybrid mode.     

Optimisation of CO2 laser beam edge‐to‐edge welding of Al‐Mg alloy sheets

Steels applied for construction of oil and gas pipelines are analysed; examples of X70 and X80 steel pipelines are given. The mechanical properties and weldability of X70 and X80 steel as well as principles of quality inspection of pipelines performed at a building site are described. On the grounds of the literature survey and the author's own experience, both shortcomings and advantages of application of advanced high-yield-strength steels, for instance X80 steel, for construction of high-pressure pipelines are presented.     

Effect of Ti content in Ag–Cu–Ti activated filler metal on dissimilar joint formation of sialon and WC–Co alloy by laser brazing

Laser brazing was carried out for dissimilar joining of sialon and a WC–Co alloy. Eutectic type Ag–Cu alloys as filler metals with different Ti content ranging from 0 to 2·8 mass-% were used to investigate the effects of Ti on the interface structure and strength of the joint. The filler metal sheet was sandwiched between a sialon block and a WC–Co alloy plate, and a laser beam was irradiated selectively on the WC–Co alloy plate. The brazed joint was obtained using the filler metal containing >0·3 mass-%Ti. TiN, Ti₅Si₃, and Cu₄Ti layers were formed at the interface of sialon and brazed metal as compound layers. The shear strength of the brazed joint increased with increasing Ti content in the filler metal in the range 0·3–1·7 mass-%, reaching a maximum value of 106 MPa. However, the strength decreased when the Ti content became higher than 1·7 mass-%.     

Effects of magnesium content on dual beam Nd : YAG laser welding of Al – Mg alloys

Abstract

The effects of Mg content on the weldability of aluminium alloy sheet using the dual-beam Nd:YAG laser welding process have been studied by making bead-on-plate welds on 1.6 mm thick AA 1100, AA 5754 (3.2 wt-%Mg) and AA 5182 (4.6 wt-%Mg) alloy sheets. Whereas all full-penetration laser welds made in 1100 aluminium were of excellent quality,many of the welds produced in the aluminium–magnesium alloys exhibited rough, spiky underbead surfaces with drop-through and undercut. A limited range of process variables was found, however, that allowed welds with acceptable weld bead quality to be produced in the 5754 and the 5182 alloy sheet. Goodwelds were only produced in these alloys if the lead/lag laser beam power ratio was ≥1. Weld penetration and the maximum welding speed allowing full penetration keyhole-mode welding were observed to increase with Mg content. This was attributed to the effect of Mg on the vapour pressure within the keyhole and the surface tension of the Al–Mg alloys. Significant occluded vapour porosity was seen in the 5754 and 5182 alloy welds with borderline penetration; however, there was no evidence of porosity in the acceptable full-penetration welds with smooth underbead surfaces. Hardness profiles in the 5754 and 5182 welds showed a gradual increase in hardness from the base metal values through the heat affected zone (HAZ) to a peak in hardness in the weld metal adjacent the fusion boundary. It is possible that this increase in hardness may be the result of the presence of Mg₂Al₃ or metastable Mg₂Al₃′ precipitates in this region of the weld and HAZ.     

Abrasive wear property of laser melting/deposited Ti2Ni/TiNi intermetallic alloy

A wear resistant intermetallic alloy consisting of TiNi primary dendrites and Ti2Ni matrix was fabricated by the laser melting deposition manufacturing process. Wear resistance of Ti2Ni/TiNi alloy was evaluated on an abrasive wear tester at room temperature under the different loads. The results show that the intermetallic alloy suffers more abrasive wear attack under low wear test load of 7, 13 and 25 N than high-chromium cast-iron. However, the intermetallic alloy exhibits better wear resistance under wear test load of 49 N. Abrasive wear of the laser melting deposition TiENi/TiNi alloy is governed by micro-cutting and plowing. Pseudoelasticity of TiNi plays an active role in contributing to abrasive wear resistance.