Influence of Adding Modifying Elements and Homogenization Annealing on Laser Melting Process of the Modified AlZnMgCu with 4%Si Alloys

AlZnMgCu, the high-strength aluminum alloy, is unsuitable for laser melting applications due to its high hot cracking sensitivity and large solidification temperature range. Adapting this alloy for laser melting processing is a high-demand research issue for extending its use. Thus, this paper investigates the effect of adding 4%Si, 4%Si-Sc+Zr, 4%Si-Ti+B, and homogenization annealing on the laser melting process (LMP) of AlZnMgCu alloy. Homogenization annealing at 500 °C for 6.5 h was selected to dissolve most of the low melting temperature phases into the grain matrix and perform stable alloys for the LMP. The pulsed laser melting process (PLM) was performed on the as-casted and the homogenized samples. The microstructures of the as-casted, the homogenized alloys, and after the LMP were evaluated. In addition, the hardness of the base metal (BM) and laser melted zone (LMZ) were measured. The results revealed that the microstructure was enhanced and refined in the as-cast state by adding the modifiers due to the increasing nucleation potency of solidification sites and the formation of primary Al3(Ti, Zr, Sc) phases. The average grain size was decreased by 15.6 times when adding 4%Si + 0.4%Zr + 0.29%Sc, while it decreased by 10.2 times when adding 4%Si + 1%Ti + 0.2%B. The LMZ of the as-casted samples exhibited a non-uniform distribution of the grains and the elements after the LMP. This was attributed to the evaporation of Zn, Mg during the high laser power process besides the non-uniform distribution of elements and phases in samples during casting. After the laser treating of the homogenized samples with 4%Si-Sc + Zr, uniform columnar grains were formed in the direction of the laser. The presence of Ti and B changed the crystallization nature, resulting in the LMZ with very fine and equiaxed grains due to forming many nucleation centers during solidification. The hardness values have positively increased due to Si addition and adding a combination of Ti + B and Sc + Zr. The maximum hardness was 153.9 ± 5 HV achieved in the LMZ of the homogenized samples of 4%Si + 1%Ti + 0.2%B.

Predicting Susceptibility to Solidification Cracking and Liquation Cracking by CALPHAD

In welding, liquation cracking can occur in the partially melted zone, leaving open cracks along the edge of the weld bead. Likewise, solidification cracking can occur in the mushy zone, leaving open cracks inside the weld bead (which is called the weld metal or fusion zone). The present study aims at demonstrating that CALPHAD-based modeling can help predict the susceptibility of alloys to both types of cracking. The basic relationship between temperature T and the fraction of solid fS of an alloy can be calculated using thermodynamic software and a database based on the alloy composition. For liquation cracking the T-fS curve of the weld metal can be compared with that of the workpiece to assess the susceptibility. For solidification cracking, on the other hand, the T-(fS)1/2 curve of the weld metal can be used to calculate the susceptibility. The composition of the weld metal depends on the compositions of the workpiece and the filler metal, and the percentage of the workpiece in the weld metal (called dilution). The susceptibility predictions based on these curves and comparison with welding experiments will be demonstrated using Al alloys, Mg alloys, and carbon steels as examples.

Intergranular corrosion susceptibility of 6061 aluminum alloy welded joints

The intergranular corrosion behavior of 6061 aluminum alloy welded joints produced by metal inert gas welding and friction stir welding was studied. The microstructure of the welded joints and the intergranular corrosion morphology of the cross-section were analyzed by optical microscopy. The results show that the most sensitive area of intergranular corrosion is the partially melted zone of the metal inert gas welding, and the maximum corrosion depth is about seven times that of the base metal, followed by the unmixed zone. The heat affected zone has the lowest sensitivity. Although the welding seam corroded seriously, general corrosion played a leading role. With the high heat input of metal inert gas welding, the sensitivity to intergranular corrosion in the partially melted zone increased significantly, while other zones had little change. For friction stir welding joints, the heat affected zone suffered from the most severe corrosion, and the nugget zone the least. However, the difference is not apparent. The susceptibility to intergranular corrosion of friction stir welding joints is weaker than that of metal inert gas welding joints but more severe than the base metal.

New Ti–35Nb–7Zr–5Ta Alloy Manufacturing by Electron Beam Melting for Medical Application Followed by High Current Pulsed Electron Beam Treatment

High-current pulsed electron-beam (PEB) treatment was applied as a surface finishing procedure for Ti–35Nb–7Zr–5Ta (TNZT) alloy produced by electron beam melting (EBM). According to the XRD results the TNZT alloy samples before and after the PEB treatment have shown mainly the single body-centered cubic (bcc) β-phase microstructures. The crystallite size, dislocation density, and microstrain remain unchanged after the PEB treatment. The investigation of the texture coefficient at the different grazing angle revealed the evolution of the crystallite orientations at the re-melted zone formed at the top of the bulk samples after the PEB treatment. The top-view SEM micrographs of the TNZT samples treated by PEB exhibited the bcc β-phase grains with an average size of ~85 μm. TEM analysis of as-manufactured TNZT alloy revealed the presence of the equiaxed β-grains with the fine dispersion of nanocrystalline α and NbTi4 phases together with β-Ti twins. Meanwhile, the β phase regions free of α phase precipitation are observed in the microstructure after the PEB irradiation. Nanoindentation tests revealed that the surface mechanical properties of the melted zone were slightly improved. However, the elastic modulus and microhardness in the heat-affected zone and the deeper regions of the sample were not changed after the treatment. Moreover, the TNZT alloy in the bulk region manufactured by EBM displayed no significant change in the corrosion resistance after the PEB treatment. Hence, it can be concluded that the PEB irradiation is a viable approach to improve the surface topography of EBM-manufactured TNZT alloy, while the most important mechanical parameters remain unchanged.

Epoxy/alumina composite coating on welded steel 316L with excellent wear and anticorrosion properties

The main purpose of this study is to elaborate anticorrosive coatings for the welded steel 316L, since this later is widely used in industrial field. Hence, within this work we have studied the electrochemical behaviour of different zones of the welded steel 316 in 1 M HCl media. The macrography study of the welded steel has revealed the different areas with a good contrast. We have stated three different zones, namely; melted zone (MZ), heat affected zone (HAZ) and base metal zone (BM). Impedance studies on welded steel 316L were conducted in 1 M HCl solution, coating of Epoxy/Alumina composite was applied on different zones, in order to reveal the anti-corrosion efficiency in each zone. Scanning electron microscopy (SEM) analysis was undertaken in order to check how far the used coating in such aggressive media protects the studied zones and these findings were assessed by water contact angle measurements. The choice of this coating is based on the cost and the safety. We concluded that the Epoxy/Alumina composite has a good protecting effect regarding welded steel in aggressive media.

On the volumes of deep carbon — the initial donor of hydrocarbons on the Earth

Existing notions on the distribution of carbon on the Earth have been considered in the article. By the example of the data on carbon content in the upper mantle of the Earth obtained in the west of the USA by deep seismic tomography method the appraisal of the resource potential of the interior has been made within the limits of the theory of the deep abiogenous-mantle origin of oil and gas. According to the given appraisal, the partly melted zone (reservoir) contains not less than 1.2·1017 kg of volatiles (Q, kg), such as H or C. Calculation by carbon (С) taking into account the initial data demonstrated that the weight content (concentration) of carbon per unit volume of the Earth crust and upper mantle for which the appraisals of carbon content were completed will be 1 333.3 kg/m3 or 1.3 t/m3 (1.3 g/cm3). With average amount of melt of the rocks of the upper mantle 0.5±0.2 % (per volume), the volume of the area of melting of the Earth crust (deep carbon reservoir), containing the appraised volume of volatiles, will be: 4.5·1011 m3. In such a notion the weight content (concentration) of carbon per unit volume of partly melted zone of deep carbon reservoir will be: 2.67·105 kg/m3 or 266.67 t/m3 (266.67 g/cm3). These are very high figures if not to say fantastically high, characterizing not only high content of carbon and hydrogen as the main donors of hydrocarbons but also characterizing concentration of these elements within definite zones of the upper mantle of the Earth (asthenospheric layer) by all components (composition, concentration, phase state, PT-conditions), which is referred by our opinion to the sources of deep oil and gas formation. The data presented allow us to affirm that the problem of donors of HC of deep, abiogenous-mantle genesis has been resolved in our concept, and the source has been determined with high probability of the primary donors of HC in the section of the mantle and iron-carbon core of the Earth having inexhaustible resources of primary carbon, with its phase composition depending on PT conditions of the terrestrial envelopes might be crystalline (diamond phase, iron and nickel compounds (Fen+Nin)+Cn, iron carbides, for example — FeC, Fe2C, Fe3C (cementite) et al.), liquid (for example, the melt with admixture of sulfur and other volatiles H-N-F-O-Cl) and gaseous (СО2 gaseous only in the mantle, higher than D″ layer). In this case HC synthesis in industrial volumes is realized in the process of hydrogenation of deep carbon on the ascending hydrogen streams within the limits of asthenospheric lenses favoured by the presence of reaction volume here, catalysts and the necessary PT-conditions for polymerization of hydrocarbon radicals.

Microstructural evolution and liquation cracking in the partially melted zone of deposited ERNiCrFe-13 filler metal subjected to TIG refusion

The microstructure of ERNiCrFe-13 multipass weld metal has been shown to contain Laves/γ or σ/γ eutectic constituents that can increase susceptibility to solidification and weld metal liquation cracking resulting from the low eutectic reaction temperature. Under poor heat dissipation conditions such as on the edge of large thickness welded components, a partially melted zone (PMZ) may form in the weld metal during multipass welding. The microstructural evolution and liquation cracking susceptibility of this PMZ in ERNiCrFe-13 multipass welds have received little attention. In the present study, a tungsten inert gas (TIG) refusion process is used to simulate a thermal cycle with a long elevated temperature dwell time in order to investigate the microstructural evolution and liquation cracking in the weld metal PMZ. The results show that the eutectic microstructures in the PMZ evolve into three eutectic morphologies after TIG refusion, including long linear chains extending perpendicular to the boundary between the refusion zone and PMZ, skeletal structures, and fine lamellar networks. This evolution contributes to constitutional liquation occurring at the γ/Laves and γ/σ interface. Nb and Mo play a leading role in the constitutional liquation of γ/Laves and γ/σ eutectic microstructures, respectively. Liquation cracking in the PMZ is shown to occur along the linear chain grain boundaries resulting from constitutional liquation.

SEM and XRD Characterisation of Fusion Lines Obtained on Austempered Ductile Iron by Laser Beam Welding without Preheating

This study highlights the weldability of austempered ductile iron (ADI) using laser welding. SEM, EDS and XRD analysis were performed on fusion lines, heat affected zone (HAZ) and melted zone (MZ). Welding speed (Ws) and laser power (P) were varied. The heat affected zone is composed of graphite, perlite and martensite; the melted and solidified zone contains graphite, ferrite and cementite. XRD results are in accordance with SEM micrographs.

Microstructure Development in the Bonding Zone of Explosively Welded Ti and Cu Sheets

The interplay of various hardening and softening processes during explosive welding and post-processing annealing have been analysed in titanium/copper bimetallic sheets using scanning electron microscopy and microhardness measurements. Severe plastic deformation and intermetallics’ formation are typical processes leading to hardening, whereas dynamic/static recrystallization and the transformation of amorphous phases into crystalline ones lead to softening. In the as-welded state the interfacial layers of both parent sheets are severely deformed. However, they can undergo intense recrystalization in areas near large melted zones. Inside the melted zones a wide variety of chemical compositions can be detected, however, most of the phases do not appear in the Ti-Cu equilibrium phase diagram. The post-processing annealing at 973 K for 1 h leads to full recrystallization of severely deformed layers of parent sheets and transforms the non-equilibrium phases forming melted zone into the equilibrium TiCu4 and Ti3Cu4 ones via spinodal decomposition. Simultaneously, the growth of four intermetallic layers: Ti2Cu, TiCu, Ti3Cu4, TiCu4 situated along the whole interface was detected.

Modeling of chemical composition in the melt pool during laser welding of Aluminum / Magnesium alloys

Joining dissimilar metals is very difficult due to the formation of brittle intermetallic phases which may be detrimental to mechanical properties. The present work aims to investigate the transport phenomenon in the weld bead and to understand the materials mixing during laser welding process of dissimilar Aluminum-Magnesium alloys. A three-dimensional transient model based on fluid flow, heat and mass transfer has been developed to predict the formation of the weld and to study numerically and experimentally the diffusion of alloying elements in the melted zone. SEM analysis of chemical composition has been realized to map elements distribution in the melted zone. The results of simulation show the formation of a heterogeneous mixture in the melt pool. The elements distribution map and the presence of brittle intermetallic phases in the fusion zone were analysed. The formation of intermetallic compounds, comprising Al3Mg2 and Al12Mg17 phases were predicted by studying the chemical elements distribution in the weld pool. A good tendency between experimental and numerical results is noticed for the weld.