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Hot cracking in AZ31 and AZ61 magnesium Alloy

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Journal of materials Science & Technology 2011年第7期27卷 633-640页

作者： c.J. Huang c.m. cheng c.P. chou F.H. chen Department of mechanical Engineering National Chiao Tung University Hsinchu 300 Taiwan China Department of Industrial Education National Taiwan Normal University Taipei 106 Taiwan China

This paper examined the impact of the number of thermal cycles and augmented strain on hot cracking in AZ31 and AZ61 magnesium alloy. Statistical analyses were performed. Following observation using a scanning electron microscope （SEm）, an energy dispersive spectrometer （EDS） was used for component analysis. Results showed that Al content in magnesium alloy has an effect on hot cracking susceptibility. In addition, the nonequilibrium solidification process produced segregation in Al content, causing higher liquid mg-alloy rich Al content at grain boundaries, and resulting into liquefied grain boundaries of partially melted zone （PmZ）. In summary, under multiple thermal cycles AZ61 produced serious liquation cracking. AZ61 has higher （6 wt%） Al content and produced much liquefied mg17Al12 at grain boundaries under multiple thermal cycles. The liquefied mg17Al12 were pulled apart and hot cracks formed at weld metal haz due to the augmented strain. Since AZ31 had half the Al content of AZ61, its hot-cracking susceptibility was lower than AZ61. In addition, AZ61 showed longer total crack length （TcL） in one thermal cycle compared to that in three thermal cycles. This phenomenon was possibly due to high-temperature gasification of Al during the welding process, which resulted in lower overall Al content. consequently, shorter hot cracks exhibited in three thermal cycles. It was found the Al content of AZ31 and AZ61 can be used to assess the hot-cracking susceptibility.

关键词： Varestraint test Thermal cycles Hot-cracking susceptibility Gas tungsten arc welding (GTAW) AZ31 AZ61

THE EFFEcT OF BORON AND cARBON ADDITION ON WELDABILITY OF DS TmS-75 SUPERALLOY

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Acta metallurgica Sinica(English Letters) 2005年第1期18卷 24-32页

作者： m.c. chaturvedi N.L. Richards Department of mechanical and Industrial Engineering University of manitoba Winnipeg Manitoba R3T 5V6 CanadaDepartment of Mechanical and Industrial Engineering University of Manitoba Winnipeg Manitoba R3T 5V6 Canada

Four alloys TmS-75 (Base), Base+B, Base+c and TmD-103 (Base+B+c) with varying levels of B, c were directionally solidified (DS), and their weldability was investigated by bead-on-plate electron beam welding. It was found that cracking occurred in the weld-metal, as well as in the heat affected zone (haz). Both γ/γ' and/or γ/carbide eutectic contributed to the weld-metal cracking, and the γ/γ' eutectic was found to be mainly responsible for cracking in haz. However, constitutional liquation of carbides seems to have made some contribution also. The B addition had a detrimental effect on haz cracking susceptibility, while c addition improved it appreciably even in the presence of B. In addition, no obvious differences were observed in cracking susceptibility of weld-metal in the four alloys. The cracking modes and mechanisms underlying the effect of B and c addition on weldability could be explained on the basis of microstructures of the four alloys.

关键词： Ni-based superalloy low melting point constituents liquation cracking

Predicting recrystallized grain size in friction stir processed 304L stainless steel

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Journal of materials Science & Technology 2019年第4期35卷 491-498页

作者： m.P.miles T.W.Nelson c.Gunter F.c.Liu L.Fourment T.mathis manufacturing Engineering Department Brigham Young University centre de mise en Forme des materiaux Mines ParisTech

A major dilemma faced in the nuclear industry is repair of stainless steel reactor components that have been exposed to neutron irradiation. When conventional fusion welding is used for repair, intergranular cracks develop in the heat-affected zone(haz). Friction stir processing(FSP), which operates at much lower peak temperatures than fusion welding, was studied as a crack repair method for irradiated 304 L stainless steel. A numerical simulation of the FSP process in 304 L was developed to predict temperatures and recrystallized grain size in the stir zone. The model employed an Eulerian finite element approach,where flow stresses for a large range of strain rates and temperatures inherent in FSP were used as input. Temperature predictions in three locations near the stir zone were accurate to within 4%, while prediction of welding power was accurate to within 5% of experimental measurements. The predicted recrystallized grain sizes ranged from 7.6 to 10.6 μm, while the experimentally measured grains sizes in the same locations ranged from 6.0 to 7.6 μm. The maximum error in predicted recrystallized grain size was about 39%, but the associated stir zone hardness from the predicted grain sizes was only different from the experiment by about 10%.

关键词： Stainless steel Numerical simulation Friction stir welding Recrystallized grain size

3-D FINITE ELEmENT ANALYSIS OF THE EFFEcT OF WELDING RESIDUAL STRESS ON HYDROGEN DIFFUSION IN HYDROGEN cONTAINED ENVIRONmENT

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Acta metallurgica Sinica(English Letters) 2007年第5期20卷 347-354页

作者： W.c. Jiang J.m. Gong J.Q. Tang H. chen S.T. Tu college of mechanical and Power Engineering Nanjing University of Technology Nanjing 210009 China

The hydrogen distribution of 16mnR steel weldment in hydrogen contained environment was calculated using the finite element method （ FEm）. The effect of welding residual stress on hydrogen diffusion has been discussed using a 3-D sequential coupling finite element analysis procedure complied by Abaqus code. The hydrogen diffusion coefficient in weld metal, the heat affected zone （haz）, and the base metal of the 16mnR steel weldment were measured using the electrochemical permeation technique. The hydrogen diffusion without the effect of stress was also calculated and compared. Owing to the existence of welding residual stress, the hydrogen concentration was obviously increased and the hydrogen woum diffuse and accumulate in the higher stress region.

关键词： 16mnR steel hydrogen diffusion welding residual stress finite element analysis

Investigation on Precipitation Transition in cGhaz for TRIP Steels containing Vanadium and Titanium

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Journal of Iron and Steel Research International 2011年第S1期18卷 154-158页

作者： cooman De B c Graduate Institute for Ferrous Technology Pohang University of Science and TechnologyPohangSouth Korea

Two kinds of low-carbon low-silicon TRIP (Transformation Induced Plasticity) steels containing vanadium are designed using Thermocalc software in the light of both thermodynamics and *** heat treatment process of different steels is determined according to the calculation results *** haz (Heat-Affected Zone) simulation tests indicate the weldability of TRIP steels is crucially sensitive to cE (carban equivelent) of the *** the impact toughness of cGhaz (coarse Grain Heat-Affected Zone) does not decrease drastically for TRIP steels microalloyed with Ti+*** steel containing both of vanadium and titanium shows smaller grain size compared with that containing vanadium *** is because the precipitation of Ti/V carbonitride slows down the grain boundary motion speed and then retards the grain size coalescence in cGhaz.

关键词： TRIP steel precipitation transition heat-affected zone cGhaz simulation

Improvement in the mechanical properties of Al/Sic nanocomposites fabricated by severe plastic deformation and friction stir processing

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International Journal of minerals,metallurgy and materials 2017年第3期24卷 297-308页

作者： m.Sarkari Khorrami m.Kazeminezhad Y.miyashita A.H.Kokabi Department of materials Science and Engineering Sharif University of Technology Department of mechanical Engineering Nagaoka University of Technology

Severely deformed aluminum sheets were processed by friction stir processing(FSP) with Si c nanoparticles under different conditions to improve the mechanical properties of both the stir zone and the heat affected zone(haz).In the case of using a simple probe and the same rotational direction(RD) of the FSP tool between passes,at least three FSP passes were required to obtain the appropriate distribution of ***,after three FSP passes,fracture occurred outward from the stir zone during transverse tensile tests;thus,the strength of the specimen was significantly lower than that of the severely deformed base material because of the softening phenomenon in the *** improve the mechanical properties of the haz,we investigated the possibility of achieving an appropriate distribution of nanoparticles using fewer FSP *** results indicated that using the threaded probe and changing the RD of the FSP tool between the passes effectively shattered the clusters of nanoparticles and led to an acceptable distribution of Si c nanoparticles after two FSP *** these cases,fracture occurred at the haz with higher strength compared to the specimen processed using three FSP passes with the same RD between the passes and with the simple *** fracture behaviors of the processed specimens are discussed in detail.

关键词： friction stir processing plastic deformation aluminum silicon carbide nanocomposites mechanical properties

mechanical properties and stress corrosion cracking behaviour of AZ31 magnesium alloy laser weldments

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Transactions of Nonferrous metals Society of china 2011年第1期21卷 1-8页

作者： P.B.SRINIVASAN S.RIEKEHR c.BLAWERT W.DIETZEL m.KO AK Institute of materials Research GKSS-Forschungszentrum Geesthacht GmbH Geesthacht D-21502Germany

An AZ31 HP magnesium alloy was laser beam welded in autogenous mode with AZ61 filler using Nd-YAG laser *** examination revealed that the laser beam weld metals obtained with or without filler material had an average grain size of about 12 μ*** microhardness and the tensile strength of the weldments were similar to those of the parent ***,the stress corrosion cracking （Scc） behaviour of both the weldments assessed by slow strain rate tensile （SSRT） tests in ASTm D1384 solution was found to be slightly inferior to that of the parent *** was observed that the stress corrosion cracks originated in the weld metal and propagated through the weld metal-haz regions in the autogenous *** the other hand,in the weldment obtained with AZ61 filler material,the crack initiation and propagation was in the haz *** localized damage of the magnesium hydroxide/oxide film formed on the surface of the specimens due to the exposure to the corrosive environment during the SSRT tests was found to be responsible for the Scc.

关键词： AZ31 magnesium alloy laser welding microstructure mechanical properties slow strain rate tensile test stress corrosion cracking fractography

EBSD characterization of microstructure and micro-texture in a Friction Stir-Welded DP600 Steel

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Acta metallurgica Sinica(English Letters) 2023年第5期36卷 789-802页

作者： H.Ashrafi m.Shamanian m.Sanayei F.Farhadi J.A.Szpunar Faculty of chemical and materials Engineering Shahrood University of TechnologyShahrood***Iran Department of materials Engineering Isfahan University of TechnologyIsfahan***Iran Department of mechanical Engineering University of SaskatchewanSaskatoonSKS7N 5A9Canada Department of materials Science and Engineering Worcester Polytechnic InstituteWorcesterMA01609USA

The microstructure and micro-texture in different areas of a friction stir(FS)-welded DP600 steel were investigated by means of electron backscatter *** volume fraction of martensite and non-polygonal ferrite was evaluated based on the image quality(IQ)*** of grain boundaries revealed that the fraction of sub-grain boundaries as well as that of low-angle grain boundaries in the heat-affected zone(haz)and stir zone(SZ)was more than doubled compared to those in the DP600 steel base metal(Bm).The micro-texture examination of the Bm showed strong{112}and{111}components with an intensity 4.6 times of that random *** texture showed a memory effect in the haz,with a reduced overall *** the SZ,D_(1),D_(2) and E shear texture components together with a cube component were *** of these texture components of ferrite were attributed to the transformation of B and R texture components of prior austenite,which are evidences of continuous dynamic recrystallization mechanism in the SZ of the friction stir-welded DP600 steel.

关键词： Dual phase steel Friction stir welding micro-texture Image quality

Effect of Heat Input on the microstructure and Properties of Dissimilar Weld Joint Between Incoloy 28 and Superaustenitic Stainless Steel

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Acta metallurgica Sinica(English Letters) 2014年第2期27卷 259-266页

作者： m.S.Abdel Rahman N.A.Abdel Raheem m.R.El Koussy Department of metallurgy Faculty of EngineeringCairo University

Abstract This work focuses on studying the effect of welding heat input within the range from 1 to 5 kJ/mm on the microstructure and the corresponding mechanical and corrosion properties of dissimilar joint between superaustenitic stainless steel （UNS S31254） and Incoloy 28 （UNS N08028）. The two materials were butt-welded with ER Nicrmo3. The metallurgical changes associated with welding of SASS and Incoloy 28 were studied using optical microscope, SEm, and EDX. The mechanical and corrosion properties were investigated using tensile test, Vickers hardness test, and pitting and crevice corrosion tests. The weld metal microstructure showed precipitates with needle-like shape at 3 and 5 kJ/mm. Also, the microstructure showed unmixed zone （UmZ） at the fusion line of both SASS and Incoloy 28 sides at all the investigated heat inputs. The mo microsegregation within UmZ at Incoloy 28 side increased as the heat input increased from 1 to 5 k J/ram but that in SASS increased with increasing heat input from 1 to 3 kJ/mm and then decreased with increasing from 3 to 5 kJ/mm. The ultimate tensile strengths for all specimens at all the investigated heat inputs are acceptable. The average hardness noticeably changed in weld metal as the heat input increased from 1 to 5 kJ/mm. Other zones such as haz or UmZ did not demonstrate marked changes in the average hardness. The pitting and crevice corrosion rates of the weld joint were found significant at l and 3 kJ/mm but insignificant at 5 kJ/mm according to ASTm G48.

关键词： Superaustenitic Incoloy 28 Welding Heat input Unmixed zone microsegregation corrosion