Development and application of flux‐paste for laser welding of aluminium alloys

Summary

A metal which rejects energy or diffuses it too easily results in an energy surplus, modifying the balance of the usual mechanisms of laser welding. The solution is to stabilise the molten pool in order to avoid such losses.     

Rational selection of semi‐finished products made from aluminium and magnesium alloys for welded structures

The results of investigation of the effect of various defects of welded joints on the fatigue resistance of welded joints are presented and used to normalize the defects taking strength characteristics into account.     

Special features of manufacture of ring‐shaped transition pieces from explosion‐welded,steel‐aluminium blanks

Coating deposition modes and techniques on the surface by manual arc under conditions of process pulsed variation of power data on the surface of parent metal and welded joints from the austenitic steels are developed.     

Special features of forming thick‐walled welded joints in brazing and fusion welding

The results of comparison of brazed scarf joints of different design on the basis of the distribution of working stresses are presented. The design of the tooth-type brazed joint is proposed and the joints are evaluated by the finite element calculations which show only a slight stress concentration in the joints of this type.     

Fatigue strength of laser‐welded lap joints

Summary

Series 6XXX and 7XXX aluminium alloys are considered to be of medium and high strength and are widely used in different industries, such as the aeronautical and automotive. However, their application as structural materials depends on the proper development of their joining processes. The present article describes the results obtained from evaluating the microstructure, using both optical microscopy (OM) and scanning electron microscopy (SEM), as well as the mechanical properties (hardness variations) of welds performed on the alloys with two different arc welding techniques: GTAW (TIG) and GMAW (MIG). For the latter, filler metal with Al-5Mg composition and A5.10-92 AWS denomination (AA5356) was used.     

Effect of backing runs on the properties of welded joints in aluminium–lithium alloys

The effect of the parameters backing runs and the composition of filler material on the properties of a welded joint and the heat-affected zone is investigated. It is shown that the porosity of the weld metal in the areas with backing runs depends strongly on the welding conditions, and when using Sv-1557 wire, the strength and plasticity are higher than those of the Sv-AMg6 wire.     

Optimisation of the processes of laser,microplasma and hybrid laser–microplasma welding of aluminium alloys

The results of investigation into laser, microplasma and hybrid laser–microplasma methods of welding aluminium alloys are presented. The optimum energy values for welding with the radiation of CO₂ lasers are determined. Shortcomings of microplasma welding are outlined and the main advantages of hybrid laser–microplasma welding are discussed. Detailed study of the macro- and microstructures of the welded joints and the heat affected zone shows that in all cases the structure is sufficiently equiaxed, dense, without visible defects and is dendritic.     

Study on microtexture of laser welded 5A90 aluminium–lithium alloys using electron backscattered diffraction

Abstract

The microtexture features of Nd:YAG laser welded joints in 5A90 aluminium–lithium (Al–Li) alloys were examined using electron back scattered diffraction (EBSD). Microtexture was determined by means of the grain orientation image maps (OIM), pole figures (PF), misorientation angles and orientation distribution function (ODF) of the weld metal (WM), heat affected zone (HAZ) and unaffected base metal (BM) of the welded joint. The results show that there is a change of microtexture in the WM and HAZ of the welded joint in terms of the component and intensity of the texture. The HAZ of the welded joint inherits the texture characteristics of the BM, whereas the welding heat input has an important influence on the component C {112}<111>. The WM of the welded joint is composed of predominantly equiaxed grains with a random microtexture.     

Modelling and numerically simulating pulsed‐arc welding of aluminium alloys

The results of investigations of surface preparation of metal structures for plasma spraying of coatings are presented and the recommendations for the selection of the surface preparation parameters using thermal abrasive tools for plasma spraying are described.     

Efficiency of using filler materials in laser welding of high-strength aluminium–lithium alloys

Investigations were carried out into the special features of the formation of the structure and properties of laser welded joints in V-1461 and V-1469 aluminium–lithium alloys. The results show that the application of the filler materials of the Al–Cu systems alloyed with rare-earth metals improves the formation of the welded joint and decreases the probability of formation of defects. Complete heat treatment of the welded joints increases their strength characteristics to 0.9 of the strength of the parent material.     

Effect of heat treatment of the mechanical properties and corrosion resistance of welded joints in high-strength aluminium–lithium alloys

Experimental results show that the maximum level of strength characteristics is obtained in complete heat treatment (quenching + artificial ageing) after welding. The heat treatment of friction stir welded joints results in the equalization of the structural heterogeneity and removal of softening in the heat-affected zone. Post-weld heat treatment conditions have almost no effect on the protective properties of non-metallic inorganic coatings. The susceptibility to intercrystalline corrosion (ICC) of welded joints with anodic oxide and chemical oxide coatings is also eliminated.     

Hydrogen permeability and corrosion‐fatigue endurance of welded joints in low‐carbon steel after laser and plasma treatment

The method of determination of the modulation parameters – the duration of additional pulses in the period of the main break and repetition frequency – is described.     

Reducing porosity in thin‐sheet welded joints in titanium alloys

The gas metal arc welding process has wide industrial applications; however, its use in the production of pressure vessels has been limited, because the welds produced do not comply with the requisites imposed by the standards that govern construction of these pieces of equipment. This work was intended to study the influence of shielding gas mixtures on ASTM A 516 grade 70 steel. Three different gas mixtures were used containing varying levels of argon, helium, carbon dioxide and oxygen. As a first step, weld beads were deposited on plates with the gas mixtures tested and morphological analyses were made of the welds obtained. Multi-pass welds were then made on joints with a ‘V’-shaped groove, for cryogenic Charpy tests. Study of the morphology of the weld beads showed that an increase in the helium gas caused greater fusion around the edges of the beads, to the detriment of penetration. The results of the Charpy test showed the best results for the mixtures that contained helium. However, oxide inclusions were seen in the samples tested, with fewer inclusions in welds produced with the helium mixtures. The higher incidences of inclusions point to a direct relationship with the lowest values of energy absorbed.     

Evaluation of properties in laser welds of A6061‐T6 aluminium alloy

In order to clarify the effect of tip velocity on the weld solidification process of hot-work tool steel (SKD61) during welding, information about microstructure evolution was obtained by the combination of a liquid tin quenching and time resolved X-ray diffraction technique using intense synchrotron radiation. From the experimental results, it was found that the solidification mode was changed from FA mode (L → L+δ → L+δ+γ → L+γ → γ) to A mode (L → L+γ → γ) at high tip velocity. Moreover, the effect of tip velocity on the microstructure selection during solidification between the primary δ, ferrite and the primary γ, austenite was theoretically proven by the Kurz, Giovanola and Trivedi model. Therefore, it was understood that the solidification cracking susceptibility of hot-work tool steel (SKD61) weld metal was increased due to the δ to γ transition of the primary phase.     

Effect of the surface roughness of friction stir welded joints on the fatigue characteristics of welded joints in V-1461 and V-1469 aluminium–lithium alloys

Investigations were carried out into the effect of friction stir welding conditions of V-1461 and V-1469 aluminium–lithium alloys on surface roughness and mechanical properties of welded joints. The general parameter of the welding conditions was the heat input coefficient determined by the ratio of the speed of rotation of the tool to the welding speed. The optimum range of friction stir welding conditions of sheets of the investigated alloys was determined. In this stage, the surface finish of the welded joint after welding is much better (required for increasing the fatigue characteristics and high-quality deposition of protective coatings), there are no defects and the strength of the welded joint is equal to 0.75–0.85 of the strength of the parent material. The production of the welded joints with reduced surface roughness (R_z ≤ 40 μm) greatly increases the fatigue characteristics of the welded joints (low-cycle fatigue strength equals more than 300,000 cycles without fracture).     

Technological aspects of assembling‐welding fuel tanks of 1460 and 1570 aluminium alloys

Results are presented on the investigation of the optimization of the temperature–time conditions of high-temperature brazing of structural steels of the austenitic (12Cr18Ni10Ti) and martensitic [06Kh15N6MVFB-Sh (VNS16) and 03Kh12NYuMTR-VD (VNS25)] grades used widely in the manufacture of heat exchangers.     

Metallurgical special features of the production of welded joints in dispersion‐filled metallic composite materials

Investigations were carried out on the special features of the structure and properties of electron beam welding joints in 150 mm thick plates of pearlitic steel 16GNMA and 160 mm plates of 12Kh2MFA steel. It is shown that using vacuum as the shielding medium results in the efficient removal of gases from the weld pool and reduces the content of alloying elements with high vapour tension.