Rotary, linear, and friction stir welding of metal alloys are solid-state joining processes in wh... more Rotary, linear, and friction stir welding of metal alloys are solid-state joining processes in which a joint between two metals can be formed by a combination of frictional heating and applied force [...]
Laser powder bed fusion (LPBF) can fabricate products with tailored mechanical and surface proper... more Laser powder bed fusion (LPBF) can fabricate products with tailored mechanical and surface properties. In fact, surface texture, roughness, pore size, the resulting fractional density, and microhardness highly depend on the processing conditions, which are very difficult to deal with. Therefore, this paper aims at investigating the relevance of the volumetric energy density (VED) that is a concise index of some governing factors with a potential operational use. This paper proves the fact that the observed experimental variation in the surface roughness, number and size of pores, the fractional density, and Vickers hardness can be explained in terms of VED that can help the investigator in dealing with several process parameters at once.
ABSTRACT In order to improve the wear resistance of parts without affecting the softer, tough int... more ABSTRACT In order to improve the wear resistance of parts without affecting the softer, tough interior of the part, laser hardening offers many advantages. Compared to conventional processes, only a shallow layer of the metal part is heated by laser irradiation to just below the melting temperature, while the surrounding material remains at ambient temperature. Due to heat conduction into the bulk material, the surface will cool down as soon as the laser beam moves away. This self-quenching creates a particularly fine-grained martensitic micro structure with high hardness without causing fragileness of the base material. Notably lower distortions of parts avoiding costly rework are produced due to laser beam follows the contours precisely. Nevertheless, when part is thin and slim even the low distortion caused by the laser hardening can deeply affects the part ability to function fairly. In this paper a double treatment is proposed in order to recover the bending and bulging deformation induced by the thermal cycle and phase transformation. Both the numerical and experimental approaches were used in a synergic attempt to rapidly achieve the goal of minimizing the displacements to a steel laser-hardened edge of a thin blade for fibers cutting application. The modeling parameters comprise geometries, laser characters, material properties and mechanical properties; the model was built by means of the finite element method. In order to validate the numerical model the experimental and numerical outputs were crosschecked. The numerical model built up for this demonstration is able to extend its predicting ability to a vast range of similar applications.
Advances in Materials Science and Engineering, 2013
2A12-T4 aluminum alloy was friction stir spot welded, and the microstructural characteristics and... more 2A12-T4 aluminum alloy was friction stir spot welded, and the microstructural characteristics and mechanical properties of the joints were investigated. A softened microstructural region existed in the joint, and it consisted of stir zone (SZ), thermal mechanically affected zone (TMAZ), and heat affected zone (HAZ). The minimum hardness was located in TMAZ, and the average hardness value in SZ can be improved by appropriately increasing welding heat input. The area of complete bonding region at the interface increased with increasing welding heat input because more interface metals were mixed. In a certain range of FSSW parameters, the tensile shear failure load of the joint increased with increasing rotation speed, but it decreased with increasing plunge rate or decreasing shoulder plunging depth. Two kinds of failure modes, that is, shear fracture mode and tensile-shear mixed fracture mode, can be observed in the tensile shear tests, and the joint that failed in the tensile-shear ...
This laser special issue has brought together academic scientists, researchers and laser manufact... more This laser special issue has brought together academic scientists, researchers and laser manufacturers for a share of their experiences on recent progress in laser science and technology in the fields of laser materials processing for manufacturing. The papers cover advances in laser materials fabrication and joining of emerging materials, their fabrication and application.
Dissimilar Ti–Al laser weldings are very interesting due to their difficulties in being processed... more Dissimilar Ti–Al laser weldings are very interesting due to their difficulties in being processed because of the different physical properties of the alloys and the crack formations during cooling and solidification. In this study, the effect of laser offset and defocusing on microstructure, geometry and mechanical properties response of 2 mm thick dissimilar AA6061/Ti-6Al-4V laser welds was analyzed. Moreover, in order to reduce residual stresses, the joints were both heat-treated and mechanically treated by ultrasonic peening. The welds microstructure was found to be martensitic in the Ti-6Al-4V fusion zone, columnar dendritic in the AA6061 fusion zone and partially martensitic in the Ti-6Al-4V heat-affected zone. Intermetallic compounds based on the Al–Ti system were detected at the AA6061/Ti-6Al-4V interface and in the aluminum fusion zone. Both negative defocusing and higher laser offset improved the tensile performance of the welds, mainly by reducing the amount of brittle int...
In this paper, hybrid laser-MAG (metal active gas) welding of twinning-induced plasticity (TWIP) ... more In this paper, hybrid laser-MAG (metal active gas) welding of twinning-induced plasticity (TWIP) and dual-phase (DP) steels with austenitic stainless steel (AISI316) was simulated by means of the finite element method. A thermo-mechanical model, which uses a 3D heat sources, was developed using the software Simufact Welding. The calculated dimensions, shape and distortion of the weld were compared with the experimental results, thence the model was validated. The metallurgical transformations for the DP steel were evaluated using the continuous cooling transformation (CCT) diagram and the calculated cooling rate. The numerical model predicted accurately the shape of the molten pool, the thermal cycles as well as the geometrical distortion of the butt weld. Therefore, the numerical model showed a good reliability and its potential for further development.
Laser surface transformation hardening (LSTH) of AISI 4130 was investigated by a Nd:YAG pulsed la... more Laser surface transformation hardening (LSTH) of AISI 4130 was investigated by a Nd:YAG pulsed laser. Laser focal height (LFH), pulse width (LPW), scanning speed (LSS), and power (LP) varied during the experiments. The microstructure of the treated zone was characterized by optical (OM) and field emission scanning electron microscopy (FESEM). Micro-hardness was measured in the width and depth directions. Results showed that the hardness and depth of hardened layer increased by decreasing the LSS and the laser focal position (LFP), and by increasing the LPW. The results were compared with those obtained by furnace heat treatment of the same steel. Eventually, a finite element model was employed for the simulation of the LSTH of AISI 4130 steel and calculation of the heat-treated zone. The results showed that the model can predict with accuracy the temperature profile and the size and the shape of the laser hardened region.
Joining dissimilar metal alloys together has become a major issue in the welding industry since t... more Joining dissimilar metal alloys together has become a major issue in the welding industry since the rapid development of innovative and performing multi-materials products. In case, titanium and Aluminum alloys can be laser-welded using a placement of the laser beam aside the weld centerline, which is called off-set. The fused zone is deep and narrow and the reaction between titanium and Aluminum is limited to a thin interlayer, which improves mechanical properties. In this paper, the effect of focus and off-set distance of the laser beam on the weldability of grade 5 titanium to 6061 Aluminum alloy dissimilar butt weld are presented. The interlayer thickness was correlated to the process parameters and tensile behavior of the weld. The map of deformation showed different deformations of the two weld sides. The data coming from the metallurgical and mechanical characterization of the weld were analyzed to figure out the best off-set and focus combination in the range studied.
Rotary, linear, and friction stir welding of metal alloys are solid-state joining processes in wh... more Rotary, linear, and friction stir welding of metal alloys are solid-state joining processes in which a joint between two metals can be formed by a combination of frictional heating and applied force [...]
Laser powder bed fusion (LPBF) can fabricate products with tailored mechanical and surface proper... more Laser powder bed fusion (LPBF) can fabricate products with tailored mechanical and surface properties. In fact, surface texture, roughness, pore size, the resulting fractional density, and microhardness highly depend on the processing conditions, which are very difficult to deal with. Therefore, this paper aims at investigating the relevance of the volumetric energy density (VED) that is a concise index of some governing factors with a potential operational use. This paper proves the fact that the observed experimental variation in the surface roughness, number and size of pores, the fractional density, and Vickers hardness can be explained in terms of VED that can help the investigator in dealing with several process parameters at once.
ABSTRACT In order to improve the wear resistance of parts without affecting the softer, tough int... more ABSTRACT In order to improve the wear resistance of parts without affecting the softer, tough interior of the part, laser hardening offers many advantages. Compared to conventional processes, only a shallow layer of the metal part is heated by laser irradiation to just below the melting temperature, while the surrounding material remains at ambient temperature. Due to heat conduction into the bulk material, the surface will cool down as soon as the laser beam moves away. This self-quenching creates a particularly fine-grained martensitic micro structure with high hardness without causing fragileness of the base material. Notably lower distortions of parts avoiding costly rework are produced due to laser beam follows the contours precisely. Nevertheless, when part is thin and slim even the low distortion caused by the laser hardening can deeply affects the part ability to function fairly. In this paper a double treatment is proposed in order to recover the bending and bulging deformation induced by the thermal cycle and phase transformation. Both the numerical and experimental approaches were used in a synergic attempt to rapidly achieve the goal of minimizing the displacements to a steel laser-hardened edge of a thin blade for fibers cutting application. The modeling parameters comprise geometries, laser characters, material properties and mechanical properties; the model was built by means of the finite element method. In order to validate the numerical model the experimental and numerical outputs were crosschecked. The numerical model built up for this demonstration is able to extend its predicting ability to a vast range of similar applications.
Advances in Materials Science and Engineering, 2013
2A12-T4 aluminum alloy was friction stir spot welded, and the microstructural characteristics and... more 2A12-T4 aluminum alloy was friction stir spot welded, and the microstructural characteristics and mechanical properties of the joints were investigated. A softened microstructural region existed in the joint, and it consisted of stir zone (SZ), thermal mechanically affected zone (TMAZ), and heat affected zone (HAZ). The minimum hardness was located in TMAZ, and the average hardness value in SZ can be improved by appropriately increasing welding heat input. The area of complete bonding region at the interface increased with increasing welding heat input because more interface metals were mixed. In a certain range of FSSW parameters, the tensile shear failure load of the joint increased with increasing rotation speed, but it decreased with increasing plunge rate or decreasing shoulder plunging depth. Two kinds of failure modes, that is, shear fracture mode and tensile-shear mixed fracture mode, can be observed in the tensile shear tests, and the joint that failed in the tensile-shear ...
This laser special issue has brought together academic scientists, researchers and laser manufact... more This laser special issue has brought together academic scientists, researchers and laser manufacturers for a share of their experiences on recent progress in laser science and technology in the fields of laser materials processing for manufacturing. The papers cover advances in laser materials fabrication and joining of emerging materials, their fabrication and application.
Dissimilar Ti–Al laser weldings are very interesting due to their difficulties in being processed... more Dissimilar Ti–Al laser weldings are very interesting due to their difficulties in being processed because of the different physical properties of the alloys and the crack formations during cooling and solidification. In this study, the effect of laser offset and defocusing on microstructure, geometry and mechanical properties response of 2 mm thick dissimilar AA6061/Ti-6Al-4V laser welds was analyzed. Moreover, in order to reduce residual stresses, the joints were both heat-treated and mechanically treated by ultrasonic peening. The welds microstructure was found to be martensitic in the Ti-6Al-4V fusion zone, columnar dendritic in the AA6061 fusion zone and partially martensitic in the Ti-6Al-4V heat-affected zone. Intermetallic compounds based on the Al–Ti system were detected at the AA6061/Ti-6Al-4V interface and in the aluminum fusion zone. Both negative defocusing and higher laser offset improved the tensile performance of the welds, mainly by reducing the amount of brittle int...
In this paper, hybrid laser-MAG (metal active gas) welding of twinning-induced plasticity (TWIP) ... more In this paper, hybrid laser-MAG (metal active gas) welding of twinning-induced plasticity (TWIP) and dual-phase (DP) steels with austenitic stainless steel (AISI316) was simulated by means of the finite element method. A thermo-mechanical model, which uses a 3D heat sources, was developed using the software Simufact Welding. The calculated dimensions, shape and distortion of the weld were compared with the experimental results, thence the model was validated. The metallurgical transformations for the DP steel were evaluated using the continuous cooling transformation (CCT) diagram and the calculated cooling rate. The numerical model predicted accurately the shape of the molten pool, the thermal cycles as well as the geometrical distortion of the butt weld. Therefore, the numerical model showed a good reliability and its potential for further development.
Laser surface transformation hardening (LSTH) of AISI 4130 was investigated by a Nd:YAG pulsed la... more Laser surface transformation hardening (LSTH) of AISI 4130 was investigated by a Nd:YAG pulsed laser. Laser focal height (LFH), pulse width (LPW), scanning speed (LSS), and power (LP) varied during the experiments. The microstructure of the treated zone was characterized by optical (OM) and field emission scanning electron microscopy (FESEM). Micro-hardness was measured in the width and depth directions. Results showed that the hardness and depth of hardened layer increased by decreasing the LSS and the laser focal position (LFP), and by increasing the LPW. The results were compared with those obtained by furnace heat treatment of the same steel. Eventually, a finite element model was employed for the simulation of the LSTH of AISI 4130 steel and calculation of the heat-treated zone. The results showed that the model can predict with accuracy the temperature profile and the size and the shape of the laser hardened region.
Joining dissimilar metal alloys together has become a major issue in the welding industry since t... more Joining dissimilar metal alloys together has become a major issue in the welding industry since the rapid development of innovative and performing multi-materials products. In case, titanium and Aluminum alloys can be laser-welded using a placement of the laser beam aside the weld centerline, which is called off-set. The fused zone is deep and narrow and the reaction between titanium and Aluminum is limited to a thin interlayer, which improves mechanical properties. In this paper, the effect of focus and off-set distance of the laser beam on the weldability of grade 5 titanium to 6061 Aluminum alloy dissimilar butt weld are presented. The interlayer thickness was correlated to the process parameters and tensile behavior of the weld. The map of deformation showed different deformations of the two weld sides. The data coming from the metallurgical and mechanical characterization of the weld were analyzed to figure out the best off-set and focus combination in the range studied.
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