Laser Beam Speed Research Articles

ВЛИЯНИЕ РЕЖИМОВ ЛАЗЕРНОЙ ОБРАБОТКИ БИМЕТАЛЛА ВТ1-0+МН19 НА СТРУКТУРУ И МИКРОМЕХАНИЧЕСКИЕ СВОЙСТВА ВАННЫ ПЕРЕПЛАВА

It has been established that during laser processing of a bimetal copper-nickel alloy MN19 + titanium VT1-0 mode with a power P = 1400 W and a laser beam speed of 0.8 m/min with a diameter of 2 mm provides optimal characteristics of the remelting bath in terms of hardness and uniformity of structure. It has been shown that a remelting bath with a homogeneous structure is ensured at a specific radiation energy of 52.52 J/mm2. In this case, an increase in the microhardness of the remelting bath by 1 GPa with an increase in the speed of movement of the laser beam and a decrease in the diameter of the spot is explained by an increase in its cooling rate.

Numerical investigation of the melt pool geometry evolution during selective laser melting of 316L SS

In this study, the melt pool size, precisely its width and depth, are numerically investigated for a wide range of values for both laser power and beam speed. A thermal model, developed on Ansys Additive Science, simulates the SLM of a single bead. A parametric study is achieved aiming at understanding the melt pool evolution and the defects appearing while varying these two parameters. The discussed porosity defects, namely the LOF and keyhole, are determined using the calculated melt pool dimensions and through mathematical correlations from the literature. Moreover, these numerical results are validated with experimental results for the reliability of the study. This investigation reveals a proportional relationship between the melt pool size and the laser power and an inversely proportional relationship with the scan speed. The optimal combination of these two parameters has to be well studied to avoid LOF and keyhole, which is afforded by this paper. At lower laser power levels, such as 100 W, it is advisable to choose a slower scan speed ranging from 400 to 500 mm/s. As the laser power increases, so does the optimal scan speed. For instance, with 150 W, the ideal speed falls between 600 to 900 mm/s. Similarly, for 200 W, the recommended scan speed range extends from 900 to 1200 mm/s, and for 250 W, the optimal speed range lies between 1100 and 1400 mm/s.

The effect of the diode laser beam power on the behaviour of the ZrC powder pre-coat and the 145Cr6 steel substrate during laser processing

The paper presents both the production method and its impact on selected properties of composite coatings reinforced with hard ZrC particles. The Fe/ZrC coatings were produced using diode laser by remelting the pre-coat in the form of paste consisting of ZrC powder and binder. Different values of laser beam power (500 W, 700 W, and 900 W) and different pre-coat thicknesses (100 µm, 150 µm, and 200 µm) were used to produce the composite coatings. During all processes, the scanning speed of laser beam was 3 m/min. Laser beam spot diameter was 1 mm. Microstructure study, microhardness tests, as well as EDS and XRD analysis were carried out. The obtained Fe/ZrC coatings were also tested for the effect of the corrosive medium in a 3.5% NaCl water solution. The effect of applied parameters on wear resistance of Fe/ZrC coatings was also studied. The tribological properties were assessed both by mass loss measurement and by scanning electron microscopy. Fe/ZrC coatings produced using the highest thickness of the pre-coat were characterised by cracks arising during production process. The very high concentration of carbides and hence high hardness of the coating produced in this way contributed to it. However, a positive effect of laser beam power increase on reduction of these cracks was observed. The coatings were characterised by very high hardness, reaching in some cases even more than 2000 HV. It was found that the most favourable properties regarding both tribology and corrosion resistance were obtained for Fe/ZrC coatings produced using 150 µm of pre-coat thickness.

Semi-Analytical Solution for Modelling Moving Heat Sources in a Semi-Infinite Medium with Radiative and Convective Boundary Conditions

The weld quality is highly related to the thermal history of the weld and there have been many trials to monitor the quality using an infrared (IR) sensor. To obtain the real temperature of a surface based on the brightness temperature values measured by an IR camera, the emissivity value must be derived. For an accurate assessment of the emissivity, one must be aware of the melting point isotherm. The temperature profiles only depend on three factors during laser processing, specified as constants the characteristics of the material: laser beam speed (v), laser beam diameter (d), and power (P). Predicting the width of the melted zone reached during the welding process as the parameters vary is a tool for helping a quality laser processing and for determination of true temperature in laser welding using IR camera. This study describes the semi-analytical (SA) solution of the heat conduction equation for a localized moving Gaussian heat source with constant parameters on a semi-infinite medium. The solution, simple and quick to obtain, provides information on the width of the melted zone with an average error < 5 %. The outcome is assessed numerically and contrasted with FEM solutions for a Gaussian source, the latter having undergone experimental validation. With two distinct defocus values, def0 and def-6, and by varying the speed and power settings, two separate types of experiments were run. Thus, the SA solution was obtained and compared after the FEM solution had been obtained with a good approximation (max err 4.3 %, average err 2.7 %). Only in regard to the 1AL test is an error more than 5 % detected; in the other case, the average error is 3.75 %. Two more tests at the defocus values of def-4 and def-8 were conducted to confirm the model's validity as the parameters varied. Overall, the average error between the semi-analytical and the FEM solution is 4.1%. The SA solution may be used to effectively estimate the isotherms related to the melting point of aluminum (770 K). This allows to obtain a tool which helps restoring the real temperature based on the brightness values measured by the IR camera during laser welding. At the same time, this effective tool allows to investigate the importance of different processing parameters in laser manufacturing.

Microstructure and hardness of laser remelted surfaces of Al-5%Cu and Al-4%Cu-1%Ni alloys

Al-based alloys are potential candidates for advanced rapid solidification processes, such as Laser Surface Remelting (LSR) and Additive Manufacturing (AM). However, currently few alloy candidates have emerged for use such as AlSi12 eutectic and AlSi10Mg. This occurs because other alloys are more susceptible to the formation of defects such as porosity, cracks and distortions, which impair high-performance applications. The addition of Ni in Al-Cu alloys is expected to improve the mechanical properties at high temperatures and favors the reduction of the solidification interval, which may decrease the fraction of solidification cracking and porosity. Given the context, the present work investigates the microstructural changes and hardness of Al-5 wt%Cu and Al-4 wt%Cu-1 wt%Ni alloys processed either by centrifugal casting or LSR. By varying laser beam speed and laser average power, a total of 4 combinations for each alloy was accomplished. The CALPHAD computations with 1%Ni alloying revealed a solidification interval reduction of approximately 30%, without reducing the total intermetallics fraction if compared to the binary Al-5%Cu alloy. The microstructure of the rapidly solidified Al-Cu-Ni samples was characterized by a dendritic α-Al matrix, surrounded by a α-Al+Al2Cu+Al7Cu4Ni constituent. A growth transition from epitaxial (bottom) to elliptical/globular (center) was observed in the molten pools with a significant cell spacing reduction from 7.5 µm (as-cast) to 0.6 µm (LSR), which favors an increase in Vickers hardness of approximately 85% if compared to the as-cast samples. The molten pool of the ternary alloy reached a higher hardness of 120 HV as a result of both AlCu and AlCuNi intermetallics acting mutually to strengthen the α-Al matrix.

Comparison of adhesive joint strength of laser fabricated dimple textured Al–Mg alloy in different environment

Joining of aluminium alloys using adhesives has got tremendous applications in aviation, marines, and unmanned aerial vehicles. Surface preparation plays a crucial role in the adhesive joining of two surfaces. In this research work, the nanosecond fibre laser was used to create dimple-shaped textures on aluminium–Mg alloy (AA5754). Dimple-shaped textures were created under three different atmospheric conditions. Experiments were performed in open-air conditions, under static water conditions, and under flowing water conditions. Texture depths differed by varying the scanning speed of laser beam. Texture pitch was also varied at two different levels, that is 300 [Formula: see text]m and 400 [Formula: see text]m in both texturing directions. Two different scanning speeds of 2.5 and 5 mm/s of the laser beam were investigated. Surface contact angle of each sample was evaluated using a goniometer to measure surface hydrophobicity/ hydrophillicity. Surface roughness and dimensions of dimples were measured using a digital microscope. Scanning electron microscopes were used to evaluate the morphology of textured surfaces. An epoxy-based adhesive (partite) was uniformly spread over textured zones and samples for standard tensile tests were prepared as per ASTM. Shear lap tensile tests were carried out to evaluate the shear lap strength of each joint on a universal testing machine. Surfaces prepared in static water conditions and flowing water conditions resulted in completely different morphology compared to open-air processing. It was observed that dimple patterns fabricated under flowing water conditions had the highest bonding strength among all the three processing environments.

Propagation characteristics of rotating beams under combined effect of atmospheric turbulence and thermal blooming

The rotating beam is a beam that is generated by the heterodyne interference of vortex beams with different topological charges, whose intensity and wavefront rotate rapidly with time. Under Taylor’s frozen air hypothesis, such a rotating beam, whose rotating period is much shorter than the characteristic time of atmospheric turbulence and the thermal blooming, can travel through all the inhomogeneities due to its rapid rotation during its propagation in the air. The rotation can contribute to the smooth of the wavefront distortion caused by the atmospheric turbulence and the thermal blooming, and thus improve the beam quality and reduce the centroid drift of the rotating beam in far field. The physical model of rotating beam is established by the heterodyne interference of two vortex beams. Taking the atmospheric turbulence and the thermal blooming effect into consideration, the propagation model of the rotating beam in the air is established by using the split-step Fourier method. For simplicity without loss of generality, the influences of the atmospheric turbulence and the thermal blooming effect on the propagation of rotating beam, are both treated as wavefront screen. The difference is that the wavefront screen of atmospheric turbulence is generated by the Kolmogorov power spectrum, while that of thermal blooming is generated by the fluid mechanics equation. The physical mechanism of how the rotating beam mitigates the atmospheric turbulence and the thermal blooming effect is analyzed in detail, that is, when the rotating speed of laser beam is faster than the airflow, the laser beam can pass through all the inhomogeneous and anisotropic atmosphere in the azimuthal direction within the time interval of airflow. After the laser propagates through the frozen air, the total wavefront distortion in the azimuthal direction becomes centrosymmetric with lower PV value, reducing the beam quality degradation. On the basis, the influence of rotation frequency, power ratio of the sub beams, strength of turbulence and thermal blooming on the propagation characteristics of the rotating beam in atmosphere are analyzed. Within a certain range, as the beam rotation frequency increases, the mitigation effect of the rotating beam on atmospheric turbulence and thermal blooming effects are enhanced. With the increase of turbulence intensity and thermal blooming intensity, the mitigation effect of the rotating beam is weakened but still can maintain well, which can provide reference for the engineering applications of laser beam in atmosphere.

Analytical and numerical analysis of the dual-pulse lag heat transfer in a three-dimensional tissue subjected to a moving multi-point laser beam

An extensive algorithm based on both analytical and numerical solution methodologies is proposed to obtain transient temperature distributions in a three-dimensional living tissue subjected to a moving single-point and multi-point laser beam by considering metabolic heat generation and blood perfusion rate. Here, the dual-phase lag/Pennes equation is analytically solved by using the method of Fourier series and the Laplace transform. The ability to model single-point or multi-point laser beams as an arbitrary function of place and time is a significant advantage of the proposed analytical approach, which can be used to solve similar heat transfer problems in other living tissues. Besides, the related heat conduction problem is numerically solved based on the finite element method. The effects of laser beam transitional speed, laser power, and the number of laser points on the temperature distribution within the skin tissue are investigated. Moreover, the temperature distribution predicted by the dual-phase lag model is compared with that of the Pennes model under different working conditions. For the studied cases, it is observed that the maximum tissue temperature decreased about 63% by an increase of 6mm/s in the speed of the laser beam. An increase in the laser power from 0.8W/cm3 to 1.2W/cm3 results in a 28 °C increase in the maximum temperature of the skin tissue. It is observed that the maximum temperature predicted by the dual-phase lag model is always lower than that of the Pennes model and the temperature variations over time are sharper, while their results are entirely consistent over the simulation time. The obtained numerical results indicated that the dual-phase lag model is preferred in heating processes occurring at short intervals. Among the investigated parameters, the laser beam speed has the most considerable effect on the difference between the results of the Pennes and the dual-phase lag models.

Grey Relational Analysis (GRA) for optimization of CO2 laser cutting of stainless steel

Laser cutting is a non-traditional industrial technique for cutting a variety of materials. The major goal of this study is to examine the influence of variables such as stand off distance, laser beam power, gas pressure and speed of cut on the width of the kerf, hardness, and roughness for CO2 laser cut of stainless steel. For the experimental plan, Taguchi's L9 orthogonal array was used. In the experiment, 4 cutting parameters were used: laser beam power (3400, 3700 and 4000 W), speed of cut (2200, 3100 and 4000 mm/min), gas pressure (0.7, 1and 1.3 bar) and stand off distance (0.6, 0.9, 1.2 mm). Laser cutting of AISI 304 stainless steel with a variety of performance characteristics is addressed using a grey grade derived from grey relational analysis. The grey grade reveal that speed of cut has a greater impact on the responses like hardness, width of the kerf and MRR than laser beam power, gas pressure and standoff distance. With this GRA technique, it is evident that the mentioned laser cutting performance characteristics can be optimized.

Microstructural Characterization of Additively Manufactured Metal Components Using Linear and Nonlinear Ultrasonic Techniques.

Metal additive manufacturing (AM) is an innovative manufacturing technology that uses a high-power laser for the layer-by-layer production of metal components. Despite many achievements in the field of AM, few studies have focused on the nondestructive characterization of microstructures, such as grain size and porosity. In this study, various microstructures of additively manufactured metal components were characterized non-destructively using linear/nonlinear ultrasonic techniques. The contributions of this study are as follows: (1) presenting correlation analyses of various microstructures (grain size and texture, lack of fusion, and porosity) and ultrasonic properties (ultrasonic velocity, attenuation, and nonlinearity parameters), (2) development of nondestructive microstructural characterization techniques for additively manufactured components; and (3) exploring the potential for the online monitoring of AM processes owing to the nondestructive nature of the proposed technique. The performance of the proposed technique was validated using additively manufactured samples under varying laser beam speed conditions. The characteristics of the target microstructures characterized using the proposed technique were consistent with the results obtained using destructive optical microscopy and electron back-scattered diffraction methods.

Influence of Laser Beam Power on Microstructure and Microhardness of Fe/ZrC Coatings Produced on Steel Using Laser Processing-Preliminary Study on the Single Laser Tracks.

This paper presents preliminary tests of the parameter analysis of the Fe/ZrC coatings production process and the obtained properties. The effects of laser beam power on the obtained microstructure, chemical composition and microhardness were investigated. The tests consisted of the production of composite coatings by laser processing of initial coatings made in the form of a paste on a steel substrate. During the tests, a diode laser with a rated power of 3 kW was used. The laser processing process was carried out using a constant scanning speed laser beam of 3 m/min and four different powers of the laser beam: 500 W, 700 W, 900 W, 1100 W. It was found that it is possible to create composite coatings on a steel surface, where the matrix is made of iron-based alloy and the reinforcing phase is ZrC carbide. It was also found that reinforcing phase content decreased as laser beam power increased. A similar relationship was found for microhardness. As laser beam power increases, the microhardness of the iron-based matrix decreases, finally reaching a value lower than the heat-affected zone. It was found that the amount of hard carbide phases in the iron-based matrix affects the total hardness of the coatings. Presented study concern Fe/ZrC coatings that have not previously been produced on steel by laser processing of precoating, which may be a new contribution in the field of metal surface engineering.

Polyamide 6-Aluminum Assembly Enhanced by Laser Microstructuring.

The presented work’s aim is the application of low-power laser treatment for the enhancement of interfacial micromechanical adhesion between polyamide 6 (filled with glass fiber) and aluminum. A fiber laser beam was used to prepare micro-patterns on aluminum sheets. The micro-structuring was conducted in the regime of 50, 100, 200 and 300 mm/s laser beam speeds, for both sides. The joining process was realized in an injection molding process. Metallic inserts were surface engraved and overmolded in one-side and two-side configurations. A lap shear test was used to examine the strength of the joints. Engraved metallic surfaces and adequate imprints on polyamide side were checked by optical microscope with motorized stages, and roughness parameters were also determined. Microscopic observations made it possible to describe the grooves’ shape and to conclude that a huge recast melt was formed when the lowest laser beam speed was applied; thus, the roughness parameter Ra reached the highest value of 16.8 μm (compared to 3.5 μm obtained for the fastest laser speed). The maximum shear force was detected for a sample prepared with the lowest scanning speed (one-sides joints), and it was 883 N, while for two-sided joints, the ultimate force was 1410 N (for a scanning speed of 200 mm/s).

Experimental study of single tracks obtained from a mixture of Ti and Al powders with varying selective laser melting parameters

The paper studies the effect of the laser scanning speed (vs) on the morphology of single tracks obtained from a mixture of Ti and Al powders in a stoichiometric ratio of 1 : 1 in longitudinal and cross sections. Droplets of splashed liquid were found on the outer surface of the track obtained at vs = 300 mm/s. Their appearance is resulted most likely from the release of gas bubbles formed due to the evaporation of aluminum having a lower melting point. A distortion of a single track along its length was observed with an increase in vs values up to 600 mm/s. It was found that tracks loose stability as the laser beam speed increases with «balls» formed on the track surface due to the significant Marangoni convection and the capillary liquid instability in the molten bath. An increase in the laser speed led to the appearance of pores mainly concentrated in the formed balls, and also influenced the track morphology in the cross section, namely, the width and height of the track, as well as the depth of substrate fusion. An increase in the scanning speed from 300 to 900 mm/s led virtually no substrate fusion, and the track width decreased from 194 to 136 μm, while its height increased almost 4 times – from 21 to 88 μm. X-ray microanalysis was conducted and element distribution maps were obtained to assess the structure of the tracks under study. It was found that the degree of liquid mixing in the molten bath is insufficient at scanning speeds of 300 and 600 mm/s, which leads to the segregation of elements over the track cross section. The central zone turns out to be enriched in aluminum, while titanium predominates at the base and is practically absent in the extreme zone (4.57 at.% Ti). X-ray microanalysis revealed the presence of unmelted titanium powder particles at vs = 900 mm/s. Presumably, it may be caused by insufficient laser power at such a high scanning speed.

Solidification and microstructure evolution in additively manufactured H13 steel via directed energy deposition: Integrated experimental and computational approach

The current work investigated additive manufacturing of H13 steel via laser aided directed energy deposition (L-DED) technique. The laser power was kept constant at 350 W, whereas, the laser beam speed was varied in the range of 5.8–14.8 mm/s (laser fluence: 77–30 J/mm 2 ). Cube samples of dimensions 2.5 × 2.5 × 2.5 cm 3 were additively manufactured. Effect of variation of processing parameters on the microstructure and phase evolution in L-DED samples was examined using X-ray diffraction, scanning electron microscopy, and electron back scatter diffraction. The complex thermokinetics involving repetitive and rapid heating/post-heating-cooling cycles experienced by the material during the L-DED process were simulated using a 3-dimensional multiphysics process model. The model was built using a multi-track multi-layer approach. Additional parameters such as the location specific ratio of thermal gradient to solidification rate (related to microstructural morphology) and multiplication of thermal gradient with solidification rate (cooling rate during solidification) were predicted from the model. The microstructure revealed signatures of cellular morphology from prior austenite grains within the transformed ferrite/martensite grain structure. The precipitates compositionally rich in carbide forming elements were detected at the cell boundaries and junctions. Bainite like morphology was revealed at a high magnification within the ferrite/martensite grain structure. The amount of retained austenite steadily decreased with an increase in the laser fluence. Hardness of the samples increased as a function of build height and the laser fluence. An integrated experimental and computational approach was developed to realize the microstructure-property evolution in the L-DED H13 steel.

Laser cladding process of Fe/WC metal matrix composite coatings on low carbon steel using Yb: YAG disk laser

The paper presents the studies of selected properties of Fe/WC metal matrix composite coatings produced using different laser beam power values and different powder feeding rates. Coatings were produced using the Yb: YAG disk laser by laser cladding method. Laser beam powers equal to 600 W, 700 W and 800 W were used. Scanning speed of laser beam was the same for all the coatings and was equal to 600 mm/min. Laser beam spot diameter was 1.64 mm. Two powder feeding rates (6.25 g/min and 12.50 g/min) were applied. In this study macroscopic observation, microstructure and microhardness examination as well as XRD and EDS analysis were carried out. Corrosion resistance was also investigated. In Fe/WC coating produced using slower powder feeding rate dendritic carbides that nucleated on the primary tungsten carbide particles were observed. In the coatings produced using an increased powder feeding rate, a changed type of secondary carbide was observed, which was bar-shaped or plate-shaped. The results of the XRD and EDS analysis of the composite Fe/WC coatings showed the presence of WC, W2C phases as well as M23C6 and (Fe,W)3C complex phases. The mechanism of formation and growth of composite coatings was described on the basis of microstructures obtained. The highest microhardness and corrosion resistance were observed for coatings produced at a powder feeding rate of 12.50 g/min.

Analysis of Gas Flow Behavior in the Laser Cutting Process using the Schlieren Method and Image Processing

The quality of laser cutting varies greatly depending on several variables, such as laser beam power, focal length, and speed. The flow of gas generated during laser cutting plays an important role in pushing the molten pool to the lower surface of the material, and is a very important factor for dross formation and spatter generation during cutting. Therefore, it is necessary to investigate the flow of gas generated during laser cutting. In this study, we captured the gas flow as a function of the inlet pressure and the stand-off distance with a high-speed camera using the Schlieren method. The images before and after gas injection were used to obtain the image intensity, which was applied to analyze the cutting gas flow for three different parts. We found that the stronger the inlet pressure and the shorter the stand-off distance, the higher the image intensity value, and the higher the gas flow rate, respectively. Key words: Laser cutting, Schlieren method, Gas flow, Image processing

Laser sealing of compostable packaging solutions: Experimental approach and adhesion mechanisms

This work aims to demonstrate the possibility of using laser technology to seal compostable coffee capsules in engineered, poly(lactic acid) (PLA) based, bioplastic material with thermoplastic starch (TPS) toplids. The welded joints were characterized by peel-off tests to evaluate the adhesion energy of the toplid to the capsule body as the laser process parameters vary, i.e. the power of the laser beam and scan speed. The results of the peel-off test made it possible to optimize the choice of laser process parameters for the various scenarios under investigation. 3D process maps were then constructed in which the adhesion index between toplid and capsule body was reported as the laser process parameters changed, allowing to identify the intervals of greatest practical relevance. In particular, the procedure allowed to define an adhesion index, a measure of the total adhesion energy between capsule body and toplid. Adhesion between conventional aluminum toplids and compostable capsules were also studied for comparative purposes. Based on the experimental findings, mechanisms of adhesion varying the material used for the toplid and capsule body were also discussed.

Experimental study of thermal fracturing of Hot Dry Rock irradiated by moving laser beam: Temperature, efficiency and porosity

Abstract A new laser irradiation fracturing method is employed to crack the Hot Dry Rock (HDR) and variations of rock temperature, specific energy (SE) and modified specific energy (MSE), thermal damages and open porosity of granite samples caused by moving laser beams with various irradiating conditions including laser power, diameter and moving speed of laser beam were investigated. Results indicate that rock temperature and the corresponding temperature gradients near the laser beam spots are strongly dependent on the laser power, beam diameter and irradiation time. The high temperature generated by the laser irradiation melts and cracks the HDR samples. The removed mass, cracked mass and size of grooving kerf induced by laser irradiation are also related to various irradiation conditions. SE and MSE are found nonlinearly reduced with the increased laser power density. Laser irradiation has a greater enhancement to thermal fracturing of granite than it does to thermal drilling. The open porosity (OP) of irradiated HDR samples increases with increasing laser power, decreasing diameter and moving speed of laser beam. The results can provide some guidance to those seeking a new economical and reasonable fracturing method for the HDR geothermal exploitation.

Microstructural change during laser welding of Inconel 718

In this study, Inconel 718 superalloy has been subjected to laser welding using a 2 kW continuous wave (CW) Yb-Fibre laser at a constant power of 1800 W with a varied scan speed of 1400 mm/min, 1200 mm/min, and 1000 mm/min, respectively. The effect of process parameters on microstructure, and microhardnes and nano-mechanical property has been studied. There is formation of reinforcement on the face of the weld zone and sometimes in the root. The weld reinforcement height has been found to vary from 51.3 μm to 72.9 μm and increases with increase in scan speed of laser beam. The microstructure of the weld zone is fine columnar in the solid liquid interface followed by dendritic region and with equiaxed morphology in the middle. In the inter-columnar, interdendritic or grain boundary regions there are presence of gamma and gamma prime precipitates. The orientation of grains in terms of micro-texture has been carefully analysed by EBSD analysis. The texture of the weld zone is marginally different from that of the base metal. There is a marginal decrease in microhardness (from 280 VHN for as-received to 246 VHN) in laser welded Inconel 718. A detailed nano-mechanical property of the weld zone has been studied by nano-hardness measurement.

Laser processing of Mg-10Li-3Al-3Zn alloy：Part II- Improving corrosion resistance of multi-phase Mg alloys by laser surface processing

In Part Ⅰ of this series, it can be found that the corrosion resistance of metals in the welded seam zone (WSZ) was far higher than that of the base metal (BM) of MBLS10A-200 Mg-Li alloy. Therefore, the feasibility of improving the corrosion resistance of MBLS10A-200 Mg-Li alloy through laser surface melting (LSM) was further explored. Meanwhile, laser shock peening (LSP) treatment was also used for contrast. The results showed that the surface melted zone with the corrosion resistance through LSM superior to that of metals in WSZ of MBLS10A-200 alloy through laser welding can be prepared by controlling heat input through increasing the scanning speed of laser beam, while LSP has limited impact on the electrochemical corrosion resistance of MBLS10A-200 alloy. The corrosion current density (Jcorr) of the samples subjected LSM declined by two orders of magnitude compared with the base metal (BM) while the charge transfer resistance increased by 17 times compared with BM. An analysis indicated that owing to the fast cooling rate during laser processing, the multi-phase microstructures (i.e. α phase, β phase and Li2MgAl) of BM were transformed into β single-phase microstructure in WSZ and surface melted zone. In this way, not only solid solution strengthening of the metals in WSZ was realized but also the micro-galvanic coupling generated due to the difference of electric potentials of multi-phase microstructures were reduced, thus improving the corrosion resistance of surface melted zone.