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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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Microstructure of intercritical heat affected zone and toughness of microalloyed steel laser welds
摘要： Microstructure of laser welds of the X70 low-carbon pipe steel was studied. High cooling rates after laser welding and non-uniform distribution of carbon in the ferrite-pearlite base metal caused formation of regions with increased microhardness (up to 650 НV) in inter-critical heat affected zone (ICHAZ). These regions consisted of finely dispersed degenerate upper bainite and martensite-austenite constituents of a slender shape and small fraction of a massive shape along the boundaries of bainite laths, as well as twinned martensite. High concentration of martensite-austenite constituents (10–16%) and residual stresses in ICHAZ, as well as a dendritic martensitic structure with carbide interlayers along the boundaries of martensite laths in fusion zone were the main reasons of sharp decrease in charpy impact energy of the welded samples. High microhardness of the laser welds was decreased down to 320 HV and their brittleness was improved by annealing. Also, in ICHAZ, degenerate upper bainite and the regions of martensite-austenite constituents decayed forming tempered sorbite and Fe2C and Fe3C carbides, respectively. Charpy impact energy of the welds doubled after annealing compared to the welds without annealing, and ductile-brittle transition temperature decreased down to –60 °С.
关键词： Toughness,Heat affected zone,Structure,Laser welding,Low-carbon steel
更新于2025-09-19 17:13:59
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Assessing Fracture Surface Ductility by Confocal Laser Scanning Microscopy
摘要： Hitherto there is no generally accepted quantitative parameter which, on the one hand, would reliably characterize the ductility of the whole fracture surface, and, on the other hand, could be relatively quickly measured. This circumstance substantially affects the objectivity of the fractographic analysis which effectiveness is still strongly dependent on the experience and skills of an expert. Recent studies showed that the value of the normalized fracture surface area Rs can serve as the measure of the fracture surface ductility. This parameter can be evaluated by the quantitative confocal laser scanning microscopy (CLSM). In the present study we investigated the Rs value for the fracture surfaces of the low carbon steel specimens tested in the temperature range from 200 to -196 °C where the steel undergoes ductile-to-brittle transition accompanied by the alternation of the fracture mode from ductile to brittle. The temperature dependence of the Rs value is found to have a sigmoidal shape with the sharp drop in the range from 100 to -100 °C. It is demonstrated that the Rs is strongly correlated with the fracture surface appearance: the Rs decreases concurrently with increasing brittleness of the fracture surface.
关键词： quantitative fractography,normalized surface area,confocal laser scanning microscopy,low-carbon steel,fracture surface
更新于2025-09-12 10:27:22