Increasing the load‐carrying capacity of spot welded joints in low‐carbon steels

It is shown to be possible to produce a heat-resisting coating for an intermetallic titanium alloy with the hardening ortho phase preventing changes in the surface layer of the alloy as a result of the build-up of oxide corrosion products, which can soften the component at working temperatures of 700–800°C. The results of investigation of the heat resistance properties, evolution of the composition and structure of the alloyed ion-plasma coatings on the titanium alloy with the hardening ortho-phase at working temperatures show that the deposition of the coating greatly reduces the depth in which the surface layer of the alloy changes and the thickness of this layer does not exceed 5 μm.     

Performance evaluation of quality monitor models in spot welding

0Introduction Uptonow,thedifficultytodevelopmonitoringtech niqueofresistancespotweldingquality,stillisthatthe weldingqualityparameters,suchassizesandstrengthof nugget,cannotbemeasureddirectly,butonlycanbede ducedindirectlyfromsomeprocessparameters.Since…     

Comparative evaluation of X‐ray test results with bend test results for aluminium alloy welded joints

The SiC particle reinforced aluminum alloy has been developed for various machine parts. Aluminum welded machine parts often require welded joints composed of dissimilar alloys. In the present study, electron beam weldability of dissimilar joints was investigated on different combinations of aluminum alloys of 10 mm thickness. The main alloy is 10% SiC particle reinforced Al–Si aluminum alloy. Combination wrought alloys are Al–Si, Al–Mg, Al–Mg–Si and Al–Zn–Mg–Cu alloys. The electron beam machine is a 6 kW high voltage type. The joint groove is of square butt without filler metal.

In the case of SiC reinforced alloy/Al–Si and Al–Mg, joints, weldability was poor because some weld imperfections were recognized such as arcing and other defects. In the case of SiC reinforced alloy/Al–Mg–Si, Al–Zn–Mg–Cu, the cracking sensitivity is low while some small porosity was recognized. Tensile strength became about 150 MPa such as SiC reinforced alloy. Impact values of the SiC reinforced alloy/Al–Mg–Si joint were recovered through 2160 h room temperature ageing. Micro segregation of the Si element was recognized for the SiC reinforced alloy/Al–Mg–Si joint by electron probe microanalyser analysis.     

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.     

Static strength of welded joints in spiral‐seam pipes

The composition of the brazing alloys for brazing niobium-based alloys is outlined. The method for producing brazing alloys based on Ti and Zr in the form of flexible strips is described. The relationships governing the formation of brazed joints are discussed.     

Residual stresses in spot welded new generation aluminium alloys Part B – finite element simulation of residual stresses in a spot weld in 5754 aluminium alloy

Abstract

An incremental thermo-electrical-mechanical coupled finite element model has been developed for predicting the residual stress field in a 5754 aluminium alloy spot welded joint. The complete spot welding process, including squeezing, welding, holding and cooling cycles, as well as the temperature and stress histories during those cycles in the welded joint have been investigated. All the required thermo-physical and thermo-mechanical properties used were experimentally measured. The results show that tensile residual stress predominates the spot nugget area. The highest tensile residual stress, with a value close to the material's yield strength, occurs around the centre of the nugget. The residual stress value decreases slightly towards the edge of the spot nugget.     

Determination of the pressurising pressure for welded thick‐wall cylindrical shells

Abstract

It is good practice to tell operators not to move a casting close to an electron beam welded joint as residual magnetism disturbs the beam trajectory; castings should, therefore be demagnetised. However, this is easy to recommend but not so easy to do as there is no universal solution to this problem. Fortunately, finite element modelling assists in solving complex cases.     

Thin‐sheet welded tailored blanks in automotive industry (review)

The results of determination of the optimum conditions of ultrasound contour welding of vessels filled with liquid products and the method of testing the strength of the welded joints are described.     

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.     

Calculation and experimental evaluation of the service life of welded joints in a nodular graphite cast iron pipeline for mechanical loading conditions. Part I ‐ experimental procedure and material

The main types of flux-cored strip electrode materials for mechanized arc surfacing of alloyed and composite alloys are discussed. Surfacing with these strips results in the formation of the required properties of the working surfaces of components. Special features of the melting and formation of the deposited layer with the required welding and technological properties are also discussed, taking into account the production technology of flux-cored strips.     

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.     

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.     

Microstructural evolution and failure characteristics of a NiCoCrAlY bond coat in “hot spot” cyclic oxidation

Microstructural evolution and the onset of failure in a NiCoCrAlY bond coat (BC) on a single-crystal superalloy substrate have been investigated in a newly developed “hot spot” apparatus that imposes a temperature gradient along the length of a coated, cylindrical specimen. Local spallation events were observed in the “hottest spot” of the coated specimens after 50–60 oxidation cycles with a peak temperature of 1050 °C. The thickness of the thermally grown oxide (TGO) was in the range of 2–3 μm when spalls were initiated. The failure surface contained a significant density of embedded oxides and the remnant TGO exhibited surface cracks indicative of a buckling delamination failure mode. The failed surface morphology and the cross-section microstructure of the BC have been characterized, including morphological imperfections in the TGO. The role of these microstructural features in the failure process is addressed.     

Static and low‐cycle strength of welded joints in a low‐alloy steel on the mesoscale level

The publications concerned with the pressure welding of cast iron are analysed. The advantages and shortcomings of individual welding methods are discussed. Examples of welding components and sections made of cast iron and of dissimilar components produced from steel and cast iron are shown. The current state of pressure welding of cast iron and prospects for the further development of this technology are outlined.     

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.     

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.