Abstract: A circular bead produced by a laser beam (CLW) is a method of joining superposed sheets by scanning circularly a laser beam. Among the various applications, it could be highlighted the welding of austenitic stainless steel AISI 304 sheets for heat exchangers. This work aims to report the effect of fiber laser CLW in tensile shear strength of superposed sheets as well as the corrosion behavior in relation to the process parameters. It was carried out circular beads using stainless steel AISI 304 sheets varying the laser power and speed. The samples were then submitted to optical and electronic microscopy, tensile-shear tests and electrochemical experiments. Among the experimental conditions, the weld sample with 800 W power and 50 mm/s speed presented an ultimate tensile strength of 159 MPa, 17% higher than the sample with the lowest result. The corrosion rate, corrosion and pitting potentials did not change significantly in the welded joint with different conditions compared to the base metal.

Abstract It was verified that SAE 4130 steel plates crack when laser beam welded at room temperature (RT). To overcome this problem, this work proposes a high temperature (HT) laser welding in order to reduce the residual stresses and create a bainitic structure instead of a martensitic one. A conventional post-welding heat treatment (PWHT) had been used as a comparison for HT. The centerline crack disappeared after a heat treatment of both in-situ (HT) or after inserting in a furnace (PWHT) at 500 °C for 10 minutes. The finite element analyses indicated a residual stress reduction from 163.70 to 3.72 MPa in the fusion zone (FZ) of the welds from RT to HT. The hardness obtained in FZ depends on the thermal cycle induced microstructure of the welds as 400 HV, 340 HV and 250 HV, for martensite (RT), tempered martensite (PWHT) and bainite (HT) micro-constituents. The proposed in-situ high-temperature laser beam welding method proved its usefulness to solve the center crack issue in SAE 4130 joints.

The effect of laser remelting on the corrosion susceptibility and mechanical properties of Ti-35Nb-4Sn (mass%) alloy is investigated across the remelted track profile. In comparison to the cold-rolled microstructure of base metal, recrystallization of heat affected zone (HAZ) improved plastic energy absorption and pitting corrosion resistance, by the reduction of active sites for pit nucleation. In fusion zone, however, passivation was compromised by the formation of dendritic microstructure with Sn enriched interdendritic region, where preferential pitting corrosion occurred. Fusion zone was the most anodic region and presented a corrosion potential difference of 35 mV, in comparison to the adjacent and most cathodic HAZ. Electrochemical impedance analysis showed that spontaneous passivation was most effective in base metal, that developed a thicker and more compact passive film. Local increase in elastic modulus and microhardness of fusion zone shows that laser remelting is a viable processing route for the manufacturing of biomaterials with functionally graded properties.

ABSTRACT Stainless steel and copper alloys joints are often applied in aerospace, marine and power industries where both high thermal and electrical conductivity (Cu) and corrosion resistance (steel) are required. In the aerospace industry, in particular for the combustion chamber of rocket engines, copper and steel combinations offer perfect materials selection due to their combined high thermal conductivity and good stiffness. In this work, laser welds were produced with intensity between 3.8 × 104 and 5.7 × 104 W/mm2 and a heat input between 72 and 108 J/mm, giving an aspect ratio of 1.8. The microstructure of the weld beads was marked by chemical heterogeneities due to the phase separation between Cu and Fe in the liquid state. The phase separation gave rise to globular precipitates which further transform due to a secondary precipitation at temperatures below 1000 °C. The steel side part of the weld presents around 20% Cu, leading to a liquation of the grain boundaries and cracking at high heat inputs. The hardness values situated between both base materials and the tensile shear behavior, when the weld is sufficiently tough, present strength up to 350 MPa and elongation up to 10%.

The effect of a surface treatment by Nd:YAG laser irradiation on the fatigue behavior of Ti-6Al-4V ELI was studied. Axial fatigue tests were performed to obtain S-N curves in polished and laser treated conditions. Roughness measurements and scanning electron microscopy were used to characterize the features of the modified surface. A reduction in the fatigue strength of around 35% was obtained after the laser treatment of the material surface. Although the surface roughness was in the micrometer scale, a notch effect was suggested to be the reason for the deleterious influence of the laser on the fatigue strength. The reduction in the fatigue strength obligatory demands redesign of implants for laser modified surfaces of Ti-6Al-4V alloy.

Abstract Laser welded Transformation-induced plasticity (TRIP) steels are known to generate martensite in the fusion (FZ) and the heat-affected (HAZ) zones. To solve this issue, the present study proposes a high temperature (HT) welding to avoid decay below the martensite start temperature after laser welding. Therefore, an inductive heating has been used to reach 500 °C before laser weld of superposed 1.6mm thick TRIP steel class 750. After welding the temperature was kept constant at 500 °C for more 10 minutes in order to austemper. The microstructures of the welds at high temperature are composed of bainite and residual austenite with an FZ hardness up to 300 HV, compared to 450 HV of the ambient temperature (AT) weld. The HT values of hardness are slightly higher than a traditional post-weld heat treatment (TW), 300 HV compared to 250 HV, because of the tempering kinetics in each case. Erichsen cup indentation tests shown the HT coupons presents better formability compared to the AT or TW conditions. The present contribution highlights a possible solution to the intrinsic brittleness during cold forming of laser welded TRIP 750 steel by applying an inductive in-situ austempering.

Resumo A solda a laser de aços com plasticidade induzida por transformação (TRIP) são conhecidos por gerar martensita nas zonas de fusão (ZF) e afetadas pelo calor (ZAC). Para resolver este problema, o presente estudo propõe uma soldagem em alta temperatura (HT) para evitar a transformação abaixo da temperatura inicial de martensita após a soldagem a laser. Assim, um aquecimento indutivo foi usado para atingir 500 °C antes da solda a laser da classe 750 de aço TRIP sobreposto de 1,6 mm de espessura. Após a soldagem, a temperatura foi mantida constante a 500 °C por mais 10 minutos para austemperar. As microestruturas das soldas em alta temperatura são compostas por bainita e austenita residual com dureza na ZF de até 300 HV, contra 450 HV da solda em temperatura ambiente (AT). Os valores da dureza HT são ligeiramente superiores ao tratamento térmico tradicional pós-soldagem (TW), 300 HV em comparação com 250 HV, devido à cinética de têmpera em cada caso. Os testes de embutimento Erichsen mostraram que as amostras HT apresentam melhor conformabilidade em comparação com as condições AT ou TW. A presente contribuição destaca uma possível solução para a fragilidade intrínseca durante a conformação a frio do aço TRIP 750 soldados a laser através da aplicação de uma austempera indutiva in situ.

ABSTRACT The heat input is the amount of energy supplied per unit length of the welded workpiece. In this study, the effect of two different heat inputs in laser beam welding of a high strength aluminum alloy AA6013-T4 was evaluated from macrostructural and microstructural points of view. The experiments were performed using a continuous wave 2 kW Yb-fiber laser with 100 µm spot size on the upper surface of the workpiece. Keeping the heat input at a given level, 13 or 30 J/mm, the laser power was changed from 650 W to 2 kW and the welding speed from 33 to 150 mm/s. In the condition of higher heat input 30 J/mm it was possible to obtain both cutting and welding processes. For 13 J/mm, welding processes were obtained in conduction and keyhole modes. The equiaxed grain fraction changed with changing speed for the same heat input. The laser processing induced a decrease in the hardness of the weld bead of about 25% due to the solubilization of the precipitates. The estimated absorptivities of the laser beam in the liquid aluminum changed largely with experimental conditions, from 4.6% to 10.5%, being the most significant source of error in measuring the real amount of energy absorbed in the process. For the same heat input the macrostructure of the welded surfaces, i.e., humps and dropouts, changed as well. All these facts indicate that the heat input is not a convenient method to parameterize the laser beam welding parameters aiming the same weld features.

The superficial coatings in micro-alloyed steel pipes has been a pointed way to decrease the corrosion problems in oil and gas industry. However, little emphasis has been given to the substrate. The effects of the deposition method on the steel microstructure and properties are still not well described. In this context, this work studied the effect of Ni superalloys clads on the phase transformations, microstructure and hardness of the heat-affected zone (HAZ) of an API steel. The underestimate of the HAZ might be dangerous, since, despite the coating good corrosion performance, the substrate HAZ may present a weak region, which may lead to an in-service coating tearing. In this work, Inconel 625 and Hastelloy C276 superalloys were clad on the steel surface by a laser deposition. Dilatometry, optical and scanning electron microscopy, and computational simulation were applied. The studied steel was originally constituted by tempered martensite. The austentizing temperature had a strong influence on the austenite grain size and on the steel CCT diagram. Due to that, the laser superalloy deposits promoted a complex HAZ, where grain growth occurred. A post-cladding heat treatment was proposed to homogenize the steel microstructure and to decrease the hardness gradient at the superalloy-steel interface.

Abstract The corrosion of C-Mn steels in the presence of hydrogen sulfide (H2S) represents a significant challenge to oil production and natural gas treatment facilities. The failure mechanism induced by hydrogen-induced cracking (HIC) in a Inconel 625 coating / C-Mn steel has not been extensively investigated in the past. In the present work, an API 5CT steel was coated with In625 alloy using laser cladding and the HIC resistance of different regions, such as the coating surface, the substrate and HAZ, were evaluated. SEM observations illustrated that all HIC cracks were formed at the hard HAZ after 96h of exposure. No HIC cracks were observed in the substrate and the In625 coating after the same exposure duration. Pitting was recorded in the substrate caused by non-metallic inclusion dissolving.

In many aerospace applications, it is important to produce hydro-repellent surfaces because water and ice accumulation could lead to malfunctioning of the part or component with a potential critical failure. In this study, it was investigated the texturing of a titanium alloy (Ti6Al4V) by applying a pulsed Nd:YAG laser, aimed at the surface characterization by microscopy, X-ray diffraction, roughness and nano-indentation tests as well as free fall drop test. The experimental procedure aimed to understand the influence of three variables: (N) the number of laser runs 1, 2, 5 and 10; (V) laser speeds of 25, 50 and 100 cm/s and (P) laser power of 5, 10 and 20 W on the microstructure and the hydrophobic behavior. The Vickers hardness and elastic modulus of laser processed surfaces were similar to the untreated surfaces. When the number of the laser runs (N) increased, a TiO phase amount increases as a result of increasing heat input. The measured roughnesses decreased with increasing P as a direct result of remelting. As the number of runs (N) increases the surface became more and more flat, consequently the overlapping runs induced polishing of the titanium surfaces. The mean roughness Ra attained 0.23 µm after 10 runs at V=100m/s and P=10W, compared to Ra=0.41 µm of the virgin surface. The water repellent conditions were N1V50P05, N1V100P05, N2V25P05, N2V50P05, N5V25P05, N5V50P05, N5V100P10 and N10V25P10. These conditions were associated with a homogeneous remelted layer, low power, partial superposition of the laser shots of 50% or 75%, and a surface finish slightly rougher than the original material.

Abstract Dual phase DP600 steels have been used in many automobile structures and laser welding has been the standard method for the joining of different sections. This work proposed a comparison between laser welding with arc welding (GMAW) and with hybrid laser-arc welding in order to access the microstructures and the mechanical behavior. The laser and hybrid welds are competitive in terms of microstructure and mechanical behavior, presenting both acceptable and tough welds. The maximum ductility of the laser and hybrid welds are very similar, around 14%, and near to the values observed in the base material. The GMAW presents low ductility due to the softening caused by tampering of the martensite, and thus is unacceptable as the welding procedure.

Duplex stainless steels have been extensively used in parts that are subject to corrosive environments and that have high mechanical strength requirements. Welding usually distorts the well-balanced austenite-ferrite ratio, and can produce brittle intermetallic phases; therefore, post-welding heat treatments are usually required. For applications where post-welding treatments are not possible, low heat input methods, such as micro-tungsten inert gas welding (TIG) and laser beam welding (LBW), can be used. The present investigation analyzed the microstructure, mechanical, and corrosion properties of 2507-classduplex steel tubes after welding. The microstructures of the heat-affected zones and the fusion zones contained variable amounts of ferrite and austenite. In the heat-affected and fusion zones in the TIG samples, the microstructures were primarily composed of ferrite grains with allotriomorphic austenite at the grain boundaries, intragranular Widmanstätten needles and plate-like precipitates. The LBW samples showed much finer microstructures, which contained austenite in the grain boundaries and fine austenite precipitates in the ferrite grains. Deleterious intermetallic phases, such as σ-phases, were not observed using X-ray diffraction. The tensile strength properties were very similar for the TIG and LBWsamples, reaching tensile strengths of approximately 840 MPa and total elongations between 61 and 87%. The heat-affected zone of the TIG welds were particularly susceptible to corrosion (0.05 mm/year) compared to the base metal (0.007 mm/year) and the laser welds (0.01 mm/year). Therefore, laser welding is a promising technique for the welding of 2507-class duplex tubes.

Three welding processes for aluminum parts have been considered for the aircraft fabrication: riveting, friction stir welding (FSW) and laser beam welding (LBW). These processes have advantages and threats, which were analyzed in the present work focusing on T-pull and Hoop tensile properties. Concerning T-pull tests, LBW coupons presented higher ability to withstand the applied loads. This was due to the better distribution of loads when the strain is done to the stringer direction. In the case of the Hoop tests, which stress only the skin, the results obtained after FSW were notably higher in terms of ultimate tensile stress, yield stress and maximum strain. It was concluded that both LBW and FSW could replace riveting usually applied for commercial aircraft manufacturing.

Três processos de união de perfis de alumínio concorrem para a manufatura de painéis estruturais (união entre revestimento e reforçadores) aeronáuticos: rebitagem, Friction Stir Welding (FSW) e soldagem a laser (Laser Beam Welding - LBW). Esses processos têm vantagens e desvantagens particulares, as quais foram analisadas no presente estudo focando, especificamente, nas propriedades de tração do conjunto unido. Dois ensaios mecânicos foram considerados, T-pull test e Hoop test. No que tange ao ensaio T-pull, as amostras soldadas por LBW apresentam maior capacidade de suportar cargas. Isso se deve à melhor distribuição de cargas, quando a solicitação mecânica se faz pelo reforçador. No caso do ensaio Hoop, onde a solicitação mecânica se dá exclusivamente no revestimento, os resultados obtidos por FSW são notadamente superiores aos obtidos pelos demais processos, em termos de tensão máxima, tensão de escoamento e de alongamento máximo. Conclui-se que tanto o LBW quanto o FSW são métodos de soldagem com possibilidade de substituir a rebitagem comumente aplicada nas aeronaves comerciais.

This paper addresses an evaluation of the influence of operational parameters used in the AISI 316 stainless steels laser welding process. The results of the welding experiments performed with parameters adjusted to a variety of situations were evaluated taking into account the power density available and the interaction time of the laser beam with the base metal. These evaluations were based on the results of microhardness and the electrolytic corrosion tests of the solders, assisted by the macrography of the weld bead. It was sought to emphasize correlations between selected operating parameters and the results obtained with weld beads, measuring their width and depth. It was concluded that the proper choice of operating parameters is fundamental to the guarantee of quality of the weld beads. Besides that, a quick method of evaluation of weld beads susceptibility was validated.

Este trabalho faz uma avaliação da influência de parâmetros operacionais utilizados no processo de soldagem a laser do aço inoxidável AISI 316. Os resultados dos experimentos de soldagem realizados com parâmetros ajustados para diversas situações foram avaliados levando em consideração a densidade de potência disponibilizada e o tempo de interação do feixe com o metal base. Essas avaliações foram baseadas nos resultados de microdureza e nos ensaios de corrosão eletrolítica das soldas, auxiliadas pela macrografia do cordão de solda. Buscou-se evidenciar correlações entre os parâmetros operacionais selecionados para os experimentos e os resultados obtidos nos cordões de solda, medindo-se grandezas como largura e profundidade. Concluiu-se que a escolha adequada dos parâmetros operacionais é fundamental para a garantia da qualidade dos cordões de solda. Além disso, validou-se um método rápido de avaliação da susceptibilidade dos cordões de solda à corrosão.

Abstract: In the aerospace industry, laser beam welding has been considered as one of the most promising routes among the new manufacturing processes. Substitution of riveting by laser beam welding of aircraft structures has contributed to weight and cost savings. Concurrently, new aluminum alloys have been developed with the addition of lithium with better mechanical properties and lower density. The Al-3.5%Cu-1.1%Li alloy (AA2198) is one of these new generation alloys. However, laser beam welding of Al-alloys expectations might be greatly reduced by the occurrence of two main defects: porosity and hot cracking. Porosity is mainly caused by the entrapment of lithium gases, followed by rapid solidification. On the other hand, hot cracking happens due to the conjunction of tensile stresses, which are transmitted to the mushy zone by the coherent solid underneath, and to an insufficient liquid feeding to compensatefor the volumetric changes. This work intended to contribute towards the knowledge of AA2198 'welding metallurgy, utilizing a 2-kW-ytterbium-dopedfiber laser. The T-joint configuration welds were performed autogenously or with the addition of an AA4047 filler ribbon. Ali the weld beads presented high porosity level, but with a decreasing tendency when welding from both sides. The use of the filler material could solve hot cracking problem. The best results are observed using two runs (both sides) with filler and a speed of 2 m/min and power of 1,200 W. The T-pull tensile strength obtained under these conditions was 178 MPa, which is below the tensile strength of the unwelded AA2198 sheet but higher than the AA6013 welded in similar conditions.