Study of aging treatment of Al‐Mg‐Si alloy laser welds. CO2 laser welding of Al‐Mg‐Si alloys (2nd report)

The main grades of high-strength steels and the methods enabling us to increase the steel strength are presented. The ways of selection of the best welding parameters for these steels are discussed and the results of mechanical testing of butt joints welded with the use of various combinations of welding consumables are presented. Advantages of application of seamless flux-cored wires for welding of high-strength steels are described.     

Study on cracking in electron beam welding of A6061 (Al‐Si‐Mg alloy)

Electron beam surfacing in an electron accelerator using powder mixtures of chromium carbides with boron carbide in different weight ratios and with different radiation parameters was used to produce wear- and corrosion-resisting coatings. It is shown that there are compositions of the surfacing mixtures and conditions of electron beam effect ensuring maximum values of wear and corrosion resistance.     

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.     

Investigation of swelling during seal‐welding of tubing and technology for its prevention: Study of welding of zirconium alloy tubing (1st report)

Summary

Swelling is liable to occur during welding of tubing which has some internal gas volume. The present study aims to clarify this phenomenon experimentally and to develop a technology for its prevention during seal‐welding of Zircaloy‐2 tubing.

Swelling occurs inside the weld metal when the pressure differential inside and outside reaches a critical value as the internal pressure increases. Swelling then develops towards the outside as the pressure increases.     

Effect of pressure on solidification cracking susceptibility of Al–Si alloys

ABSTRACT

An approach was developed to calculate the crack susceptibility under various levels of pressure, and the corresponding numerical method was presented. The binary Al–Si alloy system was selected for study because the effect of high pressure on its phase diagram has been reported. The results showed a higher pressure can lead to a higher crack susceptibility and shift the most crack susceptible composition to higher solute contents. It was found a higher pressure can increase the effect of back diffusion on the solidification path and hence the crack susceptibility. This study provides a new understanding of the effect of pressure on solidification cracking susceptibility and can be a relevant starting point for studying solidification cracking under high pressures.     

Characteristics of reheat cracking in weld metal. Study of reheat cracking in metal active‐gas welding with flux‐cored wire stainless steel weld metal (1st Report)

The processes taking place during melting and solidification of the deposited powder Sormite alloy and the factors influencing the physical–mechanical properties of the component are analysed and it is attempted to formalize the functional relationships using regression analysis. The transition zone and the deposited layer are studied by metallographic and energy-dispersing analysis. The dependence of the variation of wear resistance on the surfacing speed is determined, and the hardness and the thickness of the deposited layer are analysed. It is shown that to ensure high wear resistance of the deposited layer, it is necessary to produce layers by multilayer surfacing.     

Effects of impurity elements on solidification cracking in electron beam welding of pipeline steel. Study of all‐position electron beam welding of large diameter pipeline joints (3rd report)

Over the last decades the arsenal of highly-effective welding technologies has been supplemented by new ones, called hybrid technologies. In this paper, we characterize hybrid welding technologies such as laser-electric arc, laser-plasma, light beam-laser and laser-submerged arc as well as hybrid ‘cold’ technologies of manufacture of permanent joints, i.e. mechanical fastenings (clamped and riveted joints) and glue joints, including also mechanical-glue ones.     

Mechanism of hot cracking in the heat affected zone of repair welds. Repair weld cracking of service‐exposed HP‐modified heat‐resisting cast alloys (3rd report)

For several decades it has been possible to observe a tendency to light structures, particularly when they are destined to develop power and movement by consuming energy, especially when this energy derives from conventional fuel (petroleum derivates).

Lighter means of transport permit savings on fuel consumption and contribute to the environmental protection due to the reduction of greenhouse gases. The first approach in this direction had been the utilization of innovative materials able to offer further improved mechanical strength.

Nevertheless, this way presents natural limits depending on the loss of rigidity, hence excessive deformability even in the elastic field. This fact leads to the necessity to add stiffeners and reinforcing elements, but this at the same time means increase again the heaviness. Under these conditions more complex structural solutions step forward as the ‘sandwich’-structures manufacturable in a modular way provided with remarkable versatility in terms of design and choice of material. In the 1990s a European research project named ‘Sandwich’ financed by the European Union had given a significant contribution to the industrialization of structural solutions, which present a high level of innovations using aforementioned structures.

The present work proposes a preliminary study and several results of an investigation, which has as the main subject the production of innovative structural sandwich panels, in other words hybrid-sandwich panels in steel-aluminium assembled using two different joining technologies as laser and FSW, which can successively be connected as well to steel structures as to aluminium ones.     

Determining hot cracking index of Al–Si–Cu–Mg casting alloys calculated using effective solidification range

The possibility of determining the hot cracking index using the calculated value of the effective solidification range is investigated for multicomponent cast aluminium alloys based on the system Al–Si–Cu–Mg with Mn, Ni, Fe and Zn additives. The upper limit of the effective solidification range was calculated as the temperature of formation of 65 wt-% solid phase using Sheil model. The linear relationship of the hot cracking index and the effective solidification range in the industrial and experimental multicomponent alloys based on the Al–Si–Cu–Mg system is demonstrated.     

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.     

Modelling of microsegregation in ternary alloys: Application to the solidification of Al–Mg–Si

A fast numerical model has been developed for the quantitative prediction of microsegregation during solidification of ternary alloys. Considering a small volume of uniform temperature, the back-diffusion equations in the primary solid phase are solved in a 1-dimensional configuration using an implicit finite difference formulation with a Landau transformation onto a fixed [0,1] interval. The other phases which may precipitate during solidification are supposed to be stoichiometric and at equilibrium while the liquid is in a state of complete mixing. These calculations are coupled with phase diagram data through the use of mapping files: the liquidus surface, the monovariant lines and all the pertaining information are mapped through calls to Thermo-Calc [B. Sundman, B. Jansson and J. O. Andersson, CALPHAD, 9, 153 (1985)], prior to starting the microsegregation calculation itself. This very efficient microsegregation model can thus be coupled directly to macrosegregation computations performed at the scale of a whole casting: from the average enthalpy and concentrations variations computed at each mesh point of a casting during one time step, this microsegregation model is capable of predicting the variations of temperature, of the volume fractions of the various phases, of the liquid concentrations and of the average density. The efficiency of this coupling between microsegregation calculation and thermodynamic mapping files is demonstrated in the particular case of the Al–Mg–Si system.     

Effect of strontium on crystallization of Mg2Si phase in Al—Si—Mg casting alloys

Otical microscope and SEM were used to observe the changes of the microstructure of Al-11.6%Si-0.4% Mg alloys with varying strontium additions and the effect of strontium on the crystallization of Mg2Si phase was discussed.It is found that Mg2Si phase nucleastes on the the surfaces of the eutectic silicon flakes in the unfully modified alloys,growing as meshwork or bamboo-shoot shape,however,very few and fine Mg2Si particles phase are isolated at the boundaries of the eurectic cells in the fully modified alloys.Strontium has an important influence on the crystallization of Mg2Si phase in the Al-Si-Mg casting alloys and it is thought to be related to the increase of the amunt of dendritic αphase and the modifying degree of eutectic silicon phase.     

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…     

Preventing hot cracking in end sections of long welds in one‐sided,multi‐arc,submerged‐arc welding

Application effectiveness of a high-power fibre Yb-laser for the laser welding of metals is investigated. Expediency of the intensive laser welding conditions featuring maximal productivity and energy intensity is established.     

Determining hot cracking index of Al–Mg–Zn casting alloys calculated using effective solidification range

The possibility of determining the hot cracking index using the calculated value of the effective solidification range is investigated for multicomponent cast aluminium alloys based on the Al–Mg–Zn system with Mn, Ni, Fe and Si additives. The upper limit of the effective solidification range was calculated as the temperature of formation of a 65?wt-% solid phase using the Sheil model. The linear relationship of the hot cracking index and the effective solidification range in the industrial and experimental multicomponent alloys based on the Al–Mg–(Zn) system is demonstrated.     

Stress-corrosion cracking of aged AlCuMg alloys in NaCl solution

Pitting potentials and stress corrosion life-times of AlCuMg alloys (mainly 2024 alloy) with various ageing structures have been measured in a de-aerated 1M NaCl solution under conditions of controlled potential. The aged alloy, which has the higher susceptibility to stress-corrosion cracking, showed two pitting potentials corresponding to pitting at the grain boundaries and within the grains. The susceptibility of the alloys to intergranular stress-corrosion cracking occurred at potentials above the pitting potential of the grain boundaries. The intergranular stress-corrosion cracking is caused not by the dissolution of the grain boundary precipitates (S phase) but by the pitting dissolution of the solute-denuded zones along the grain boundaries. Aspects of SCC in the alloys are similar to those in the Al-4%Cu alloy without Mg.     

Microstructural changes in weld metal during isothermal process. Study of reheat cracking in flux‐cored arc welding stainless steel weld metal (5th report)

The soiling of the slag, spatter and the fume, etc., which come into contact with the steel sheet surface with welding, is cleaned making use of steel sphere shot material of large particle diameter, high projection pressure with strong peening processing (below, called strong peening cleaning). In this research, the cleaning state of the soiling with welding and improvement of fatigue strength of the hot galvanized welded joint was inspected, when the surface of a SM490A welded joint was cleaned with strong peening cleaning.

The following experimental results were obtained:

1. The fatigue limit of smooth base metal which received strong peening cleaning at about 320 MPa was remarkably high in comparison with smooth base metal at about 245 MPa.

2. The fatigue limit of a welded joint which received strong peening cleaning at about 300 MPa was remarkably high in comparison with a welded joint at about 170 MPa.

3. The strong peening cleaning was highly efficient and the cleaning state was satisfactory.

4. The cause of the remarkable rise of the fatigue limit (300 MPa) of the welded joint which received strong peening cleaning was because the fatigue limit (about 170 MPa, 57%) of the welded joint was improved (about 130 MPa, 43%) with peening cleaning. It was considered that improvement effects were: a rise (about 68 MPa, 23%) of hardness of the weld toe; relief (about 43 MPa, 14%) of stress concentration; increase (about 136 MPa, 45%) of compressive residual stress; and the decrease (about ? 96 MPa, ? 32%) by increase of surface roughness.

5. The fatigue strength of the hot galvanized welded joint decreased remarkably. This was thought to be due to the decrease (about HV40) of hardness of the surface, the decrease (about 188 MPa) of the compressive residual stress and the influence of many factors which accompanied hot galvanizing.

     

Gas tungsten arc welding process for surfacing of aluminium alloys with Al‐Cu cored wire 2nd report: Surfacing of aluminium alloy

Abstract

In alloy steels, ferrite is formed during the solidification of the metal. Structure of the steel changes depending on the content of austenite (nickel, carbon, nitrogen, manganese, copper and cobalt) – and ferrite-forming (chromium, molybdenum, silicon, tungsten, vanadium, aluminium, titanium and niobium) elements.¹ According to the current state of knowledge, the structure of the weld at ambient temperature depends on the content of ferrite which existed at very high temperatures (below the liquidus curve), i.e. it depends on the ratio of the austenite–ferrite forming elements. Welds in 18–10 grade steels, after cooling to ambient temperatures, have austenitic–ferritic structures.