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Microstructure and properties of high strength and high conductivity Cu-Cr alloy components fabricated by high power selective laser melting
摘要： Although different kinds of metal materials have been built in the past years, it is difficult to fabricate the components of copper alloys with high strength and high conductivity due to their high reflectivity and thermal conductivity. In this paper, Cu-Cr alloy with high strength and high conductivity was successfully manufactured by high laser power selective laser melting. The microstructure, mechanical properties and conductivity were studied and compared before and after the heat treatment. The microstructure of the as-built sample was columnar grains with very fine cellular sub-structures and precipitates of Cr and Cr2O3. After heat treatment, the Cr particles precipitated from Cu matrix, resulting in simultaneous increase in strength and conductivity. The ultimate tensile strength of 468 MPa, yield strength of 377.33 MPa, and electrical conductivity of 98.31% IACS were achieved, which is even better than the samples fabricated by rolling with post heat treatment.
关键词： Cu-Cr alloy,Electronic conductivity,Laser processing,Microstructure,Mechanical properties
更新于2025-11-28 14:24:20
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Effects of Substrate Preheating Temperatures on the Microstructure, Properties, and Residual Stress of 12CrNi2 Prepared by Laser Cladding Deposition Technique
摘要： The 12CrNi2 alloy steel powder studied in the present paper is mainly used to manufacture camshafts for nuclear power emergency diesel engines. Laser cladding deposition is of great signi?cance for the manufacture of nuclear power emergency diesel camshafts, which has the advantages of reducing material cost and shortening the manufacturing cycle. However, due to the extremely uneven heating of the components during the deposition process, a complex residual stress ?eld occurs, resulting in crack defects and residual deformation of the components. In the present paper, 12CrNi2 bulk specimens were prepared on the Q460E high-strength structural steel substrate at different preheating temperatures by laser cladding deposition technique, and a ?nite element residual stress analysis model was established to investigate the effects of different preheating temperatures on the microstructure, properties, and residual stress of the specimens. The results of the experiments and ?nite element simulations show that with the increase of preheating temperature, the content of martensite/bainite in the deposited layer decreases, and the ferrite content increases. The proper preheating temperature (150 ?C) has good mechanical properties. The residual stress on the surface of each specimen decreases with the increase of the preheating temperature. The longitudinal stress is greater at the rear-end deposition part, and the lateral residual stress is greater on both sides along the scanning direction.
关键词： substrate preheating,12CrNi2 alloy steel powder,residual stress,laser cladding deposition,microstructure and properties
更新于2025-11-28 14:24:20
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Analysis of microstructure and mechanical strength of lap joints of TZM alloy welded by a fiber laser
摘要： The application of molybdenum alloys to structural components is severely limited due to their poor weldability with serious defects of porosity and joint embrittlement after welding despite their high melting temperature, hot strength and creep resistance. A systematical experimental study has been conducted to explore the potential of laser welding of 0.5 mm-thick Titanium-zirconium-molybdenum (TZM) alloy in a lap welding configuration. Porosity was found to be the most serious problem in the TZM laser lap welding process. Introducing an interface gap of 0.09 mm had the most positive effect in reducing the porosity compared to using helium gas, different shielding gas flow rates, adding alloy element and different heat input rate. With the use of 0.09 mm-interface gap, the porosity of the weld joint was reduced to 3%. The tensile stress of the bead on plate (BOP) welded joint could achieve about 60% that of the base metal. The fracture stress of the lap welded joint obtained by using 0.09 mm-interface gap in tensile-shear test was about 142 MPa. The porosity and embrittlement were responsible for the reduction of the strength and ductility of the welded joint.
关键词： Porosity,Mechanical property,Molybdenum alloy,Laser welding
更新于2025-11-28 14:24:20
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Effect of Heat Input on Porosity Defects in a Fiber Laser Welded Socket-Joint Made of Powder Metallurgy Molybdenum Alloy
摘要： Porosity defects are still a challenging issue in the fusion welding of molybdenum and its alloys due to the pre-existing interior defects associated with the powder metallurgy process. Fiber laser welding of end plug and cladding tube made of nanostructured high-strength molybdenum (NS-Mo) alloy was performed in this work with an emphasis on the role of welding heat input. The distribution and morphology of porosity defects in the welded joints were examined by computed tomography (CT) and scanning electron microscopy (SEM). Preliminary results showed that laser welding of NS-Mo under low heat input significantly reduced the porosity defects in the fusion zone. The results of computed tomography (CT) showed that when the welding heat input decreased from 3600 J/cm (i.e., 1200 W, 0.2 m/min) to 250 J/cm (i.e., 2500 W, 6 m/min), the porosity ratio of the NS-Mo joints declined from 10.7% to 2.1%. Notable porosity defects under high heat input were related to the instability of the keyhole, expansion and the merging of bubbles in the molten pool, among which the instability of the keyhole played the dominant role. The porous defects at low heat input were generated as bubbles released from the powder metallurgy base metal (BM) did not have enough time to overflow and escape.
关键词： fiber laser welding,molybdenum alloy,porosity defects,heat input
更新于2025-11-28 14:24:20
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Mechanism study on the effects of power modulation on energy coupling efficiency in infrared laser welding of highly-reflective materials
摘要： High-reflectivity of materials, such as magnesium, copper and aluminum, results in low thermal efficiency of their infrared laser welding processes. AZ31 magnesium alloy was selected to study the effects of power modulation on energy coupling efficiency in laser welding of highly-reflective materials. A model for the relationship between energy coupling efficiency and modulation parameters was obtained. The energy coupling efficiency in optimized modulated-power laser welding was about 1.58 times that in constant-power welding. The mechanism was explored by analyzing keyhole evolution and the resulted pressure distribution along keyhole wall during welding. The keyhole evolutions in laser continuous welding of common material (Q345 steel, reflectivity of 65%) and highly-reflective material (AZ31, reflectivity of 85%) were observed through high-speed imaging by utilizing a half sandwich method. The results indicated that the secret of improving energy coupling efficiency of laser welding process of highly-reflective materials through power modulation was the formation of a deep keyhole and its long life. When instantaneous power decreased from the peak, there was still enough recoil pressure at the bottom of keyhole to resist surface tension and hydrostatic pressure of liquid metal, which was the fundamental reason for the long time existence of keyhole with a large depth.
关键词： laser welding,magnesium alloy,recoil pressure,keyhole,highly-reflective materials,power modulation
更新于2025-11-28 14:24:20
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Effects of Power Modulation, Multipass Remelting and Zr Addition Upon Porosity Defects in Laser Seal Welding of End Plug to Thin-Walled Molybdenum Alloy
摘要： Aiming to solve the serious porosity defects in laser welded girth joints of thin-walled tube and end plug made of nano-sized Ce2O3 doped Mo alloy (NC-Mo), the influences of laser power modulation, multipass remelting and zirconium (Zr) addition on the number, size and distribution of porosity defects were experimentally studied. By utilizing X-ray computed tomography (XCT), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) analysis, transmission electron microscope (TEM) and Raman spectrum (RS), the porosity feature of welded joints achieved under various conditions was analyzed. The results showed that welding cycles had a significant influence on the porosity ratio of fusion zone (FZ) while the amplitude and frequency of laser power waveform slightly influenced the porosity. When the welding cycles increased from 2 to 8, the porosity ratio of FZ decreased from about 1.00% to about 0.48% and the maximum and average pore diameters reduced by about 53% and 27%, respectively. Adding minor Zr in molten pool can further reduce the RP of FZ to about 0.35%. Through analysis, it can be seen that the pores in FZ can be divided into irregularly-shaped keyhole-induced pores and spherical metallurgy-induced pores. The latter was generated possibly because some impurity elements (including O and H) pre-existing in base metal (BM). Increasing welding cycles can promote the gas in molten pool to float and outflow, thus significantly decreasing the porosity. Moreover, Zr added in molten pool can be preferentially reacted with O to generate ZrO2, which can inhibit the precipitation of volatile MoO2 to thus suppress the generation of metallurgy-induced pores.
关键词： Molybdenum alloy,Multipass remelting,Power-Modulated laser welding,Zirconium addition,Porosity
更新于2025-11-28 14:24:20
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Butt welding-brazing of steel to aluminum by hybrid laser-CMT
摘要： A laser penetration welding-brazing combined with Cold Metal Transfer (CMT) arc, was proposed to improve weld shape and interfacial reaction inhomogeneity of 5052 aluminum alloy and Q235 low carbon steel with ER5356 welding wire in butt joint. The effects of wire feed speed, beam offset and welding speed on weld shape, interfacial microstructures and tensile strength of joints was studied. This method improved the undercut defect existed in butt laser welding-brazing, obtained well-formed joints and promoted the uniform distribution of the interface reaction. The interfacial intermetallic compounds (IMCs) layer consisted of Fe2Al5 and Fe4Al13 and the thicknesses were controlled to 3-5 μm. Microstructures of weld seam was composed of α-Al and Al3Mg2. The brittle IMCs layer thickened and then the tensile strength decreased with increasing the wire feed speed. The thickness of the IMCs layer decreased but weld shape became worse when the welding speed or the offset increased. The tensile strength increased first and then decreased. The highest tensile strength reached higher than 80 MPa and the joint fractured in IMCs layer along the interface.
关键词： intermetallic compound,Laser–CMT arc hybrid welding-brazing,dissimilar metals welding,low carbon steel,aluminum alloy
更新于2025-11-28 14:24:20
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Laser welding of AZ31B magnesium alloy with beam oscillation
摘要： Circular beam oscillation was introduced to laser welding of 2 mm-thick AZ31 magnesium alloy. The appearance, microstructure and tensile properties of the welds were investigated. It was found that the low frequency about 50 Hz and the small radius about 0.5 mm are more beneficial to improve the weld appearance, under the given parameters of laser power 2 kW, welding speed 2 m/min and beam oscillating diameter 0.35 mm. The undercut defect and even the totally collapse of the weld appear when employing the frequency higher than 75 Hz or the radius larger than 1.5 mm. The microstructure evolution mainly reflects in the variation of the proportions of the equiaxed zone (PEZ) and the average grain size (SG). The PEZ decreases from 85% to 42% with the beam oscillating frequency increasing from 25 Hz to 100 Hz, while the SG reaches the maximum of 37.5 μm at 75 Hz. The PEZ decreases and the SG increases with the increase of beam oscillating radius. The results showed that the tensile strength and elongation are closely related to the PEZ, the SG and the twins. According to the experimental results, the relationship of oscillating parameters, microstructure, and tensile properties was established.
关键词： Laser oscillating welding,Magnesium alloy,Microstructure,Tensile properties
更新于2025-11-28 14:24:20
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Microstructural Characteristics of Laser Metal Deposited Magnesium Alloy AZ31
摘要： Up to now, only a limited amount of metallic materials is investigated for laser additive manufacturing (LAM). However, the demand to widen the application possibilities by enlarging the range of materials for LAM is growing fast. By now, titanium and aluminium alloys are in the focus of research. In contrast, magnesium alloys are rarely used in the field of additive manufacturing, although they possess a low density in combination with a high specific strength. Currently, magnesium structures are mainly produced by casting but during the last years, the use of wrought alloys also increased. A reason for the rare use of magnesium alloys for LAM technologies might be the high flammability of magnesium powders. This difficulty can be avoided by using magnesium wire for laser metal deposition (LMD). In the present study, the microstructural characteristics of a LMD processed AZ31 magnesium alloy are investigated. For this purpose, optical microscopy and scanning electron microscopy were used. With the help of EDX and EBSD analysis, a change of the chemical composition and micro texture with structure height was identified. The relationship of microstructure and local mechanical properties was investigated with the help of Vickers micro hardness testing. Based on the obtained results it can be concluded that the microstructural characteristics of laser additive manufactured magnesium alloys differ from those of titanium and aluminium alloys. Thus, a wider application spectrum of LMD and magnesium alloys can be opened up.
关键词： laser metal deposition,local mechanical properties,microstructure,magnesium alloy,wire,microtexture
更新于2025-11-28 14:24:20
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A Comparative Study of Deformation Behaviors Between Laser-Welded Joints and Base Metal of Ti-22Al-24.5Nb-0.5Mo Alloy
摘要： The tensile deformation behaviors of laser-welded Ti-22Al-24.5Nb-0.5Mo alloy joints have been investigated at room temperature and 650 °C using in situ tensile analysis methods. The a2 phase had a significant influence on deformation behaviors of base metal at room temperature and 650 °C. The microcracks mainly nucleated in B2/a2 phase boundaries or within a2 phase and then propagated along B2/a2 phase boundaries subsequently. Compared with the plastic fracture of base metal, the fracture modes of the fully B2-phase fusion zone at room temperature and 650 °C were quasi-cleavage and intergranular fracture, respectively. While dislocation slips became foremost deformation mode in the fusion zone at room temperature, there were a great amount of slip bands on the surface of grains caused by the slip systems. The microcracks of fusion zone at 650 °C nucleated and propagated along the grain boundaries of B2 phase. Owing to the lack of grain deformation, the cross-slip bands were in small quantities on the surface of B2 phase grains.
关键词： in situ analysis,laser welding,deformation behaviors,Ti2AlNb alloy
更新于2025-11-28 14:24:20