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...
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 [...]
The friction stir lap welding of AA5083 H111 aluminum alloy and S355J2 grade DH36 structural stee... more The friction stir lap welding of AA5083 H111 aluminum alloy and S355J2 grade DH36 structural steel was investigated. A polycrystalline cubic boron nitride with tungsten and rhenium additives tool was used. According to visual inspection, radiographic examination, and tensile test, it was observed that the best results were obtained for rotation speeds of about 700–800 rpm, with a feed speed ranging between 1.3 and 1.9 mm/s. From the fatigue tests, it is possible to state that there was a preferential propagation of cracks in the part of the aluminum alloy base material. Furthermore, a different response to fatigue stress for samples extracted from the same weld at different positions was observed, which introduces an overall variability in weld behavior along the welding direction. The specimens obtained in the second part of the weld endured a larger number of cycles before reaching failure, which can be related to progressively varying thermal conditions, dissipation behavior, and...
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.
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.
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 this paper, TWinning-Induced Plasticity (TWIP), Dual Phase (DP) and austenitic stainl... more Abstract In this paper, TWinning-Induced Plasticity (TWIP), Dual Phase (DP) and austenitic stainless (AISI 316) steels were joined together by hybrid laser/arc welding with an austenitic steel filler. Microstructural and mechanical characterization of welded joints was carried out by optical microscopy, microhardness, tensile and bend tests. The heat affected zone (HAZ) at the TWIP side was fully austenitic and exhibited a grain coarsening; at the DP side, new martensite formed close to the fusion zone and other phase transformations occurred moving toward the base metal; at the AISI 316 side, stringers of untreated ferrite δ inside the austenitic matrix was observed. All the tensile welded specimens broke within austenitic stainless steel. TWIP/AISI 316 welds exhibited a greater tensile strength than DP/AISI 316 ones. The bending tests confirmed the ductility of both sorts of joints.
Abstract In this paper, an innovative 18% Mn austenitic TWIP steel, which exhibits a very good co... more Abstract In this paper, an innovative 18% Mn austenitic TWIP steel, which exhibits a very good combination of strength and ductility, was joined by laser arc hybrid welding to a conventional DP steel, which consists of ferrite and martensite obtained by an inter-critical heat treatment and fast cooling. An austenitic filler wire was used to improve the weld strength by avoiding the formation of Mn segregations and improper microstructures in the fusion zone by Mn dilution. Metallographic examinations, microhardness and tensile tests were carried out to assess the effects of the laser and materials interaction on the weldability of TWIP-DP dissimilar welds. Hybrid welding and austenitic filler can have a positive effect on the weldability of the DP-TWIP dissimilar joint.
Abstract In this study, AISI 304 and AISI 410 stainless steels were welded together by a fiber la... more Abstract In this study, AISI 304 and AISI 410 stainless steels were welded together by a fiber laser-TIG hybrid welding system. Weldability was evaluated through the characterization of the microstructure and mechanical properties. The effects of welding parameters, such as laser line energy (ratio between laser power and feed rate) and arc current, were analyzed. Welds microstructure and defects were assessed and related to the tensile test, type of fracture and residual stress. The latter was measured in the normal and longitudinal directions respect to the weld line. The difference observed in the two sides of the weld were highlighted and commented. FZ microstructure resulted predominantly martensitic, which increased the micro-hardness up to an average value of about 350 HV. Porosity reached a minimum, about 0.2%, when the maximum values were used for laser line energy and arc current. Maximum elongation was as far as 4.87% and the tensile strength as big as 391 MPa. Residual stresses were much lower than the ultimate tensile and yield stresses. Eventually, the paper demonstrated the good and easy weldability of dissimilar austenitic and martensitic stainless steels in annealed condition by fiber laser coupled with an electric arc.
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.
Among the machining errors generated in the peripheral milling the dimensional accuracy and surfa... more Among the machining errors generated in the peripheral milling the dimensional accuracy and surface roughness play a fundamental role in the quality of the machined component in the automotive and aerospace industry. The inadequacy of the surface roughness and the imprecision of the dimensional accuracy brings to the rejection of the part that causes financial loss and productivity slowdown.In this paper an analysis of the machining errors due to the cutting forces in peripheral milling was performed by means of a numerical model based on the finite element method. The dynamic cutting forces distribution were evaluated for several cutting conditions that varied with the effective rake angle, the axial depth of cut, the radial depth of cut and the feed per tooth per revolution.The model was tested with the cutting forces measured by Yucesan and Altintas in field trials on a titanium alloy. An analytical model furnished by Liu et al. and calibrated with the Yucesan’s results gave a benchmark to the discussion of the results of this paper.
The residual stress in steel welding can highly influences the performance of the joint during it... more The residual stress in steel welding can highly influences the performance of the joint during its working life. Both boundary conditions and metal phase transformations have influence on the levels of the residual stress in the weld. In this paper the residual stress for AISI 4047 bead-on-plate samples were measured by strain gage method after laser welding with different values for the laser speed and power, and focus height. The laser used for this project was the ROFIN DC 015 Industrial CO2 Slab Laser. This laser, registered as class 4 laser product in accordance with the European Norm EN 60825 is an high frequency excited, diffusion cooled C02 gas laser, designed to be used for processing materials in a industrial environment. The measurement procedure was performed on all the welded specimens taking notes of 3 strains (ε1 ε2 ε3) relative to as many gages at different depths, following the American Society for Testing Materials (ASTM) standard. Thereafter the residual stresses ...
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...
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 [...]
The friction stir lap welding of AA5083 H111 aluminum alloy and S355J2 grade DH36 structural stee... more The friction stir lap welding of AA5083 H111 aluminum alloy and S355J2 grade DH36 structural steel was investigated. A polycrystalline cubic boron nitride with tungsten and rhenium additives tool was used. According to visual inspection, radiographic examination, and tensile test, it was observed that the best results were obtained for rotation speeds of about 700–800 rpm, with a feed speed ranging between 1.3 and 1.9 mm/s. From the fatigue tests, it is possible to state that there was a preferential propagation of cracks in the part of the aluminum alloy base material. Furthermore, a different response to fatigue stress for samples extracted from the same weld at different positions was observed, which introduces an overall variability in weld behavior along the welding direction. The specimens obtained in the second part of the weld endured a larger number of cycles before reaching failure, which can be related to progressively varying thermal conditions, dissipation behavior, and...
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.
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.
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 this paper, TWinning-Induced Plasticity (TWIP), Dual Phase (DP) and austenitic stainl... more Abstract In this paper, TWinning-Induced Plasticity (TWIP), Dual Phase (DP) and austenitic stainless (AISI 316) steels were joined together by hybrid laser/arc welding with an austenitic steel filler. Microstructural and mechanical characterization of welded joints was carried out by optical microscopy, microhardness, tensile and bend tests. The heat affected zone (HAZ) at the TWIP side was fully austenitic and exhibited a grain coarsening; at the DP side, new martensite formed close to the fusion zone and other phase transformations occurred moving toward the base metal; at the AISI 316 side, stringers of untreated ferrite δ inside the austenitic matrix was observed. All the tensile welded specimens broke within austenitic stainless steel. TWIP/AISI 316 welds exhibited a greater tensile strength than DP/AISI 316 ones. The bending tests confirmed the ductility of both sorts of joints.
Abstract In this paper, an innovative 18% Mn austenitic TWIP steel, which exhibits a very good co... more Abstract In this paper, an innovative 18% Mn austenitic TWIP steel, which exhibits a very good combination of strength and ductility, was joined by laser arc hybrid welding to a conventional DP steel, which consists of ferrite and martensite obtained by an inter-critical heat treatment and fast cooling. An austenitic filler wire was used to improve the weld strength by avoiding the formation of Mn segregations and improper microstructures in the fusion zone by Mn dilution. Metallographic examinations, microhardness and tensile tests were carried out to assess the effects of the laser and materials interaction on the weldability of TWIP-DP dissimilar welds. Hybrid welding and austenitic filler can have a positive effect on the weldability of the DP-TWIP dissimilar joint.
Abstract In this study, AISI 304 and AISI 410 stainless steels were welded together by a fiber la... more Abstract In this study, AISI 304 and AISI 410 stainless steels were welded together by a fiber laser-TIG hybrid welding system. Weldability was evaluated through the characterization of the microstructure and mechanical properties. The effects of welding parameters, such as laser line energy (ratio between laser power and feed rate) and arc current, were analyzed. Welds microstructure and defects were assessed and related to the tensile test, type of fracture and residual stress. The latter was measured in the normal and longitudinal directions respect to the weld line. The difference observed in the two sides of the weld were highlighted and commented. FZ microstructure resulted predominantly martensitic, which increased the micro-hardness up to an average value of about 350 HV. Porosity reached a minimum, about 0.2%, when the maximum values were used for laser line energy and arc current. Maximum elongation was as far as 4.87% and the tensile strength as big as 391 MPa. Residual stresses were much lower than the ultimate tensile and yield stresses. Eventually, the paper demonstrated the good and easy weldability of dissimilar austenitic and martensitic stainless steels in annealed condition by fiber laser coupled with an electric arc.
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.
Among the machining errors generated in the peripheral milling the dimensional accuracy and surfa... more Among the machining errors generated in the peripheral milling the dimensional accuracy and surface roughness play a fundamental role in the quality of the machined component in the automotive and aerospace industry. The inadequacy of the surface roughness and the imprecision of the dimensional accuracy brings to the rejection of the part that causes financial loss and productivity slowdown.In this paper an analysis of the machining errors due to the cutting forces in peripheral milling was performed by means of a numerical model based on the finite element method. The dynamic cutting forces distribution were evaluated for several cutting conditions that varied with the effective rake angle, the axial depth of cut, the radial depth of cut and the feed per tooth per revolution.The model was tested with the cutting forces measured by Yucesan and Altintas in field trials on a titanium alloy. An analytical model furnished by Liu et al. and calibrated with the Yucesan’s results gave a benchmark to the discussion of the results of this paper.
The residual stress in steel welding can highly influences the performance of the joint during it... more The residual stress in steel welding can highly influences the performance of the joint during its working life. Both boundary conditions and metal phase transformations have influence on the levels of the residual stress in the weld. In this paper the residual stress for AISI 4047 bead-on-plate samples were measured by strain gage method after laser welding with different values for the laser speed and power, and focus height. The laser used for this project was the ROFIN DC 015 Industrial CO2 Slab Laser. This laser, registered as class 4 laser product in accordance with the European Norm EN 60825 is an high frequency excited, diffusion cooled C02 gas laser, designed to be used for processing materials in a industrial environment. The measurement procedure was performed on all the welded specimens taking notes of 3 strains (ε1 ε2 ε3) relative to as many gages at different depths, following the American Society for Testing Materials (ASTM) standard. Thereafter the residual stresses ...
Uploads
Papers by Giuseppe Casalino