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 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.     

Growth features of crystals in laser‐welded aluminium and aluminium alloys

In the present work, the increase in the basicity index of the slag system of the flux, represented by the ternary system of MnO–SiO₂–CaO oxides, is evaluated. The increment of the basicity index is performed by the addition of CaO, keeping the MnO/SiO₂ percentage relation of the system constant, in order to evaluate the behaviour of the chemical composition resulting from the metal deposited by SAW. As a result, it is possible to intensify the Mn transfer to the deposited metal and at the same time attenuate that of the Si, S, P and the carbon remains basically unalterable. All this makes it possible, in combination with low-manganese wire, to obtain similar results to those obtained with fluxes of lower basicity in combination with medium manganese wires.     

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).     

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.     

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.     

Increasing the reliability of welded joints in high-strength V-1461 aluminium–lithium alloy

Filler materials for welding V-1461 alloy, ensuring high cracking resistance, corrosion resistance and mechanical properties, are selected. The results of tests of the welded joints in static tensile loading and bending and the impact toughness of the weld metal and low-cycle fatigue strength are presented. The experimental results show that the application of impact ultrasound treatment increases by an order of magnitude the values of low-cycle fatigue resistance of the welded joints as a result of the formation of the nanostructured surface layers. The level of residual stresses in welded joints is determined.     

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.     

Localized tensile strain distribution and metallurgy of electron beam welded Ti–5Al–5V–5Mo–3Cr titanium alloys

The tensile properties, strain distribution, fracture mechanisms, and microstructure of electron beam welded Ti–5Al–5V–5Mo–3Cr (Ti–5553) in the as-welded condition were investigated in order to evaluate the weldability of the titanium alloy. Rolled sheets of Ti–5553 were electron beam welded perpendicular to the rolling direction and sub-size tensile specimens were machined from the sheets. Tensile tests were conducted in conjunction with the use of a non-contact 3D image correlation photogrammetry system, ARAMIS, to determine the as-welded tensile properties as well as localized strain in the vicinity of the weld zone. Microstructural examination showed the fusion zone and heat affected zones consisted of large grains of retained β phase whereas the base metals consisted of α surrounding small β grains containing dispersed α precipitates. Tensile tests revealed that elongation at fracture in the as-welded condition was comparable to un-welded Ti–5553 while also revealing that the tensile strength was lower. Hardness profiles across the welds showed a decrease in average hardness from the base metals to the fusion zone. The decrease in hardness can be attributed to the large grain size, retained β phase, and loss of Al during welding. Fracture occurred in the weld zone and was primarily due to microvoid coalescence. These results indicate that Ti–5553 is readily weldable and displays reasonable properties in the as-welded condition.     

Micromechanism of failure in off-centre tensile loading of fusion welded joints in 1422 high-strength aluminium–lithium alloy

The results of the investigation of the micromechanisms of failure and special features of the morphology of fracture of various sections of fusion welded joints in 1422 aluminium–lithium alloy in relation to the position of the stress concentrator with respect to applied load in off-centre tensile loading are presented.     

Mechanical properties and microstructures of hybrid laser MIG welded dissimilar Mg–Al–Zn alloys

Abstract

Bead shape, microstructure changes and mechanical properties of laser metal inert gas (MIG) welded dissimilar Mg–Al–Zn alloys (from AZ31B to AZ61) are studied. The results show that heat ratio of arc to laser (HRAL) and welding speed are dominant parameters for achieving good tensile strength efficiency and elongation property. From AZ31B to AZ61, microstructure changes are observed as cellular dendrites to equiaxed dendrites and fish bone dendrites in the upper part of hybrid weld. Besides, at weld centreline, the solidification structure of lower part is finer than that of upper part. In this study, the maximum tensile strength efficiency and elongation reached 97·6 and 7% respectively. When the HRAL matches welding speed well, the joint achieves higher tensile strength with 45° shearing fracture at heat affected zone because of fewer defects. However, when utilising too low HRAL or fast welding speed, the joints show lower tensile strengths with nearly vertical fracture at fusion zone.     

Friction stir welding of V-1461 and V-1469 high strength aluminium–lithium alloys

The problems of the technology of friction stir welding (FSW) of new high-strength aluminium–titanium alloys V-1461 and V-1469 are discussed. The technical and economical advantages of the process are shown, the parameters are determined and the optimum FSW conditions resulting in high mechanical properties of the welded joint are proposed.     

Mechanical properties of A6082 welded joints with Nd–YAG laser

Weldability of A6082 with Nd–YAG laser was investigated to explain the advantages over the conventional MIG process. It is concluded that rapid cooling rate in heat-affected zone (HAZ) contributes to increasing joint strength and improvement durability against liquation cracking in HAZ during Nd–YAG laser welding. This is why rapid cooling rate is enough to prevent crossing the C-curve for precipitation of β′ and small volume of weld metal is enough to reduce shrinkage strain during solidification. And the joint strength increased with an increase of manganese content in the base metal, but by contraries the minimum hardness in HAZ where the fracture occurred in the tensile test decreased. This may be attributed to the prevention of intercrystalline embrittlement due to the addition of manganese in case of Al–Mg–Si series alloys with excessive Si content.     

A method of stabilising the process of electron beam welding aluminium‐ and magnesium‐based alloys

The development of electronic power sources for welding has allowed the study of innovative processes, generally with the objective of improving the capacity of production linked to low levels of thermal support. The existing processes are based on the metal transfer mode and on the development of wave forms that improve control of the process. The metal inert gas-variable polarity pulsed process is a derivative of the conventional metal inert gas process that combines the advantages of the use of positive polarity, such as good arc stability and cathode cleaning, with those given by negative polarity, principally the high fusion rate of the electrode and low thermal support to the base metal. However, this process has only found limited use due to the scarcity of technical and scientific publications. As a result, this work sets out a proposal for a methodology to determine welding parameters in four different wave formats and varying the negative electrode rate across three levels in a way that provided arc and metal transfer stability, the evaluation of the process was carried out by filming the arc and analysing the geometric characteristics of the weld bead. The method was shown to be sufficiently efficient with satisfactory stability results.     

Effect of united refining and modification on mechanical properties of A356 aluminium alloys

The refining and modification effect of Ti （from GRA/）, B, Sr and RE （cerium-riched mixtures of rare earth） on the mechanical properties ofA356 aluminum alloys under T5 and T6 treatment condition were studied by OM, SEM, EDAX, etc. It is found that the addition of RE to A356 alloys containing Ti and/or B and Sr makes strength and elongation increase in T6 treatment, but make elongation decrease in T5 treatment, at the same time, the long axis of α（Al） grain structure decreases and the mean diameters of silicon particles increase with RE additions increasing. Grain refining with 0.01%Ti plus 0.03% B makes the dendrite a（Al） grain structure transform into equiaxed structure, resulting in obvious increase of elongation percentage. The mean diameters of silicon particles in T5 treatment are smaller than that in T6 treatment. Roundness of silicon particles in T5 treatment is higher than that in T6 treatment. A356 alloys modified and refined with Ti, B and Sr obtain the best mechanical properties in T5 treatment, however, the alloys with Ti, B, RE and Sr additions obtain the best mechanical properties in T6 treatment.     

Corrosion resistance of calcium-modified zinc phosphate conversion coatings on magnesium–aluminium alloys

The influence of the microstructure of the calcium-modified zinc phosphate (Zn–Ca–P) conversion coatings of Mg–Al alloys on corrosion resistance was investigated using OM and SEM and hydrogen evolution tests. The results demonstrated that the Zn–Ca–P coatings markedly enhanced the corrosion resistance of the alloys. The microstructure and chemical compositions of the alloys exerted a significant influence on the corrosion resistance of their coatings. A model was proposed to elucidate the formation mechanism of the porous Zn–Ca–P coating on the AM30 alloy.     

FIB-SEM investigation on corrosion propagation of aluminium–lithium alloy in sodium chloride solution

Abstract

Microstructural characterisation of 2A97-T4 aluminium–lithium alloy was carried out using electron probe microanalysis and transmission electron microscopy (TEM). Scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy facilities has been employed to examine localised corrosion sites after immersion in sodium chloride solution. A dual beam microscope, which integrates a focused ion beam and an electron beam in one powerful instrument, has also been employed to investigate the development of intergranular corrosion from both surface and cross-section. It was found that localised corrosion is generally initiated at θ phase particles, which represents only 8.4% of the intermetallic (IM) particles in 2A97-T4 aluminium–lithium alloy. θ phase particles exhibit preferential dissolution of aluminium during corrosion testing, with trench formed at their periphery as well. Initiation of intergranular corrosion is relatively late with respect to the attack of IM particles. Owing to the presence of θ phase particles at intergranular corrosion sites and non-uniform distribution of T1 (Al₂CuLi) grain boundary precipitates, it is supposed that dealloyed θ phase particles and grain boundary precipitates cooperate to provide the driving force for grain boundary attack.     

Special features of using alloys of the iron–aluminium system for protective coatings of casting moulds

The effect of twin-arc surfacing conditions using aluminium and steel electrode wires on the chemical composition of deposited metal is investigated. The effect of the chemical composition on the mechanical and service properties of deposited layers is described and the efficiency of using intermetallic alloys of the iron–aluminium system as permanent protective coatings of casting moulds is confirmed.