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1.
Temperature and velocity fields, and weld pool geometry during gas metal arc welding (GMAW) of commercially pure aluminum were predicted by solving equations of conservation of mass, energy and momentum in a three-dimensional transient model. Influence of welding speed was studied. In order to validate the model, welding experiments were conducted under the similar conditions. The calculated geometry of the weld pool were in good agreement with the corresponding experimental results. It was found that an increase in the welding speed results in a decrease peak temperature and maximum velocity in the weld pool, weld pool dimensions and width of the heat-affected zone (HAZ). Dimensionless analyses were employed to understand the importance of heat transfer by convection and the roles of various driving forces in the weld pool. According to dimensionless analyses droplet driving force strongly affected fluid flow in the weld pool. 相似文献
2.
Recent computer calculations of heat transfer and fluid flow in welding were intended to provide useful insight about weldment
geometry for certain specific welding conditions and alloys joined. However, no generally applicable correlation for the joining
of all materials under various welding conditions was sought in previous work. To address this difficulty, computer models
of fluid flow and heat transfer were used for the prediction of weld pool geometry in materials with diverse properties, such
as gallium, pure aluminum, aluminum alloy 5182, pure iron, steel, titanium, and sodium nitrate under various welding conditions.
From the results, a generally applicable relationship was developed between Peclet (Pe) and Marangoni (Ma) numbers. For a
given material, Ma and Pe increased with the increase in laser power and decrease in beam radius. For materials with high
Prandtl number (Pr), such as sodium nitrate, the Pe and Ma were high, and heat was transported primarily by convection within
the weld pool. The resulting welds were shallow and wide. For low Pr number materials, like aluminum, the Pe and Ma were low
in most cases, and low Pe made the weld pool deep and narrow. The cross-sectional areas of stationary and low speed welds
could be correlated with welding conditions and material properties using dimensionless numbers proposed in this article. 相似文献
3.
A study of laser energy transfer efficiency, melting efficiency, and deposition efficiency has been conducted for the laser-engineered
net-shaping process (LENS) for H-13 tool steel and copper powder deposits on H-13 tool steel substrates. This study focused
on the effects of laser deposition processing parameters (laser power, travel speed, and powder mass flow rate) on laser beam
absorption by the substrate material. Measurements revealed that laser energy transfer efficiency ranged from 30 to 50 pct.
Laser beam coupling was found to be relatively insensitive to the range of processing parameters tested. Melting efficiency
was found to increase with increasing laser input power, travel speed, and powder mass flow rate. A dimensionless parameter
model that has been used to predict melting efficiency for laser beam welding processing was investigated for the LENS process.
From these results, a semiempirical model was developed specifically for the LENS processing window. Deposition efficiency
was also investigated and results show that under optimum processing conditions, the maximum deposition efficiency was approximately
14 pct. A semiempirical relation was developed to estimate deposition efficiency as a function of process efficiencies and
LENS processing parameters. Knowledge of LENS process efficiencies measured in this study is useful to develop accurate heat
flow and solidification models for the LENS process. 相似文献
4.
In the area of laser welding, numerous studies have been performed in the past decades using either analytical or numerical
approaches, or both combined. However, most of the previous studies were process oriented and modeled conduction and keyhold
welding differently. In this research, various heat source equations that have been proposed in previous studies were calculated
and compared with a new model. This is to address the problem of predicting, by numerical means, the thermomechanical behavior
of laser spot welding for thin stainless steel plates. A finite-element model (FEM) code, ABAQUS, is used for the heat transfer
and mechanical analysis with a three-dimensional plane assumption. Experimental studies of laser spot welding and measurement
of thermal deformation have also been conducted to validate the numerical models presented. The results suggest that temperature
profiels and weld deformation vary according to the heat source equation of the laser beam. For this reason, it is essential
to incorporate an accurate model of the heat source. 相似文献
5.
J. Wadsworth A. R. Pelton R. E. Lewis 《Metallurgical and Materials Transactions A》1985,16(12):2319-2332
Superplastic properties have been developed in Al-Cu-Li-Mg-Zr alloys. The alloys have low Zr levels (≤0.2 wt pct) and are
experimental compositions that were originally designed as low-density, highmodulus, and high strength alloys for room temperature,
aerospace structural applications. The alloys have been manufactured both by an ingot metallurgy (IM) route and a powder metallurgy
(PM) route involving rapid solidification processing. After conventional manufacturing, the alloys are not superplastic but
require further thermomechanical processing. The microstructural changes that occur during this processing are described.
Superplastic properties have been evaluated as a function of temperature, strain rate, and processing history. Prior to thermomechanical
processing, the alloys have elevated-temperature ductilities of 100 to 200 pct, strain rate sensitivities of about 0.25, and
activation energies corresponding to lattice diffusion. After thermomechanical processing, the alloys have ductilities of
500 to 1000 pct, strain rate sensitivities of about 0.4, and activation energies corresponding to grain boundary diffusion.
In addition, room temperature properties have been measured in the solution-treated and peak aged (T6) condition for all the
alloys and comparison is made with other commercial, non-Li containing, superplastic alloys. Particular emphasis is placed
on properties of interest in aerospace applications such as specific modulus, specific strength, and a buckling failure criterion. 相似文献
6.
An experimental study of the calcination of limestone has been carried out in a highly instrumented pilot-scale rotary kiln.
Local gas, solids, and wall temperatures and pct calcination have been measured under a range of operating conditions to determine
the influence of limestone type, feed rate, rotational speed, inclination angle, and particle size on calcination and heat
flow in the kiln. Thus, it has been found that the local calcination is dependent primarily on the solids temperature and
hence on heat transfer. Of the variables studied, the limestone feed rate has the strongest effect on the temperature and
calcination fields, whereas inclination angle and rotational speed are relatively less important. The different limestones
studied exhibited significant differences in heat-absorption capacity and calcination temperature which may be related to
their radiative properties. Increasing particle size over a range of 0.75 to 3.5 mm resulted in an increase in both heat transfer
to the bed and calcination. 相似文献
7.
8.
Sindo Kou 《Metallurgical and Materials Transactions A》1981,12(12):2025-2030
Based on the finite difference method and the enthalpy model of Shamsundar, a computer model was developed to describe the
steady state, two-dimensional heat flow during the welding of thin plates. In order to allow accurate computations of the
weld pool configuration, the size of the mushy zone and the temperature distribution near the heat source, a grid mesh of
variable spacings was used. The heat of fusion, the size and distribution of the heat source, the temperature dependence of
thermal properties, the heat conduction in the welding direction and the surface heat loss during welding were considered.
The model was first checked with Rosenthal’s analytical solution of welding heat flow using pure aluminum for examples. Experimental
results of 6061 aluminum, including the width of the fusion zone and the thermal cycles at positions in both the fusion and
the heat affected zones, were then compared with the calculated results of the heat flow model. The agreement was very good.
Finally, in order to demonstrate systematically the quantitative effect of welding parameters such as the heat input, the
welding speed and the preheating of the workpiece, a series of computations were made based upon 6061 aluminum. 相似文献
9.
Because joining dissimilar metals is often difficult by fusion joining, interest has been growing rapidly in using friction
stir welding (FSW), which is considered a revolutionary solid-state welding process, as a new way to join dissimilar metals
such as Al alloys to Mg alloys, Cu, and steels. Butt FSW of Al to Mg alloys has been studied frequently recently, but the
basic issue of how the welding conditions affect the resultant joint strength still is not well understood. Using the widely
used alloys 6061 Al and AZ31 Mg, the current study investigated the effect of the welding conditions, including the positions
of Al and Mg with respect to the welding tool, the tool travel speed, and the tool rotation speed on the weld strength. Unlike
previous studies, the current study (1) determined the heat input by both torque and temperature measurements during FSW,
(2) used color metallography with Al, Mg, Al3Mg2, and Al12Mg17 all shown in different colors to reveal clearly the formation of intermetallic compounds and material flow in the stir zone,
which are known to affect the joint strength significantly, and (3) determined the windows for travel and rotation speeds
to optimize the joint strength for various material positions. The current study demonstrated clearly that the welding conditions
affect the heat input, which in turn affects (1) the formation of intermetallics and even liquid and (2) material flow. Thus,
the effect of welding conditions in Al-to-Mg butt FSW on the joint strength now can be explained. 相似文献
10.
Zhenzhen Yu Wei Zhang Hahn Choo Zhili Feng 《Metallurgical and Materials Transactions A》2012,43(2):724-737
A three-dimensional transient computational fluid dynamics (CFD) model was developed to investigate the material flow and
heat transfer during friction stir processing (FSP) in an AZ31B magnesium alloy. The material was assumed to be a non-Newtonian
viscoplastic fluid, and the Zener-Hollomon parameter was used to describe the dependence of material viscosity on temperature
and strain rate. The material constants used in the constitutive equation were determined experimentally from compression
tests of the AZ31B Mg alloy under a wide range of strain rates and temperatures. A dynamic mesh method, combining both Lagrangian
and Eulerian formulations, was used to capture the material flow induced by the movement of the threaded tool pin. Massless
inert particles were embedded in the simulation domain to track the detailed history of material flow. The actual FSP was
also carried out on a wrought Mg plate where temperature profiles were recorded by embedding thermocouples. The predicted
transient temperature history was found to be consistent with that measured during FSP. Finally, the influence of the thread
on the simulated results of thermal history and material flow was studied by comparing two models: one with threaded pin and
the other with smooth pin surface. 相似文献
11.
K. B. Bisen M. Arenas N. El-Kaddah V. L. Acoff 《Metallurgical and Materials Transactions A》2003,34(10):2273-2279
Previous research by the authors has shown that the welding current has a strong effect on the weld properties and microstructures
of gamma TiAl. This article presents the results of experimentally measured and theoretically predicted temperature profiles
of gas tungsten arc (GTA) welded gamma TiAl for welding currents of 75 and 100 A. The GTA welding model used in this study
accounts for the fluid flow in the weld pool as well as conductive, convective, and phase change heat transfer processes in
the solid, liquid, and mushy regions of a metal. The computed temperature fields predicted that as the welding current is
increased, the maximum temperature reached in the weld pool also increases. Experimental validation of the computed temperature
fields was determined by placing thermocouples at three locations on the specimen, to record the temperatures during welding
using computer-based data acquisition hardware and software. The agreement between theoretical predictions and measurements
was reasonably good, which provided a direct validation of the model.
This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented
at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint
Committee on Mechanical Behavior of Materials. 相似文献
12.
13.
J-P. Immarigeon Krishna Rajan W. Wallace 《Metallurgical and Materials Transactions A》1984,15(2):339-345
Interest has evolved recently in thermomechanical processing of the cast Co-Cr-Mo surgical implant alloys such as Vitallium
and Vinertia. Work has shown that the wrought forms of these alloys exhibit much improved properties over their as-cast counterparts.
In this paper, the response of as-cast Vinertia to isothermal forging is examined by means of isothermal and isostrain-rate
compression testing. The effects of temperature, strain rate, and strain on the breakdown of the as-cast micro-structure are
examined in detail. The effects of prior heat treatment on plastic flow and microstructure achieved are also considered. It
is shown that the interaction between the carbide phase and the recrystallization induced during hot working governs the degree
of homogeneity that can be achieved in the forged product. Control of carbide volume fraction, size, and distribution by appropriate
prior processing can lead to a fine grain equiaxed structure with uniformly distributed carbides. The potential offered by
isothermal forging for control of the microstructure in this type of alloy is discussed, as well as the limits imposed on
the process by the starting material and by the strain gradients expected during the forging of implants. 相似文献
14.
Florian A. Besler Richard J. Grant Paul Schindele Michael J. R. Stegmüller 《Metallurgical and Materials Transactions B》2017,48(6):2930-2948
Joining sheet metal can be problematic using traditional friction welding techniques. Friction crush welding (FCW) offers a high speed process which requires a simple edge preparation and can be applied to out-of-plane geometries. In this work, an implementation of FCW was employed using an additional wire to weld sheets of EN AW5754 H22, DC01, and Cu-DHP. The joint is formed by bringing together two sheet metal parts, introducing a wire into the weld zone and employing a rotating disk which is subject to an external force. The requirements of the welding preparation and the fundamental process variables are shown. Thermal measurements were taken which give evidence about the maximum temperature in the welding center and the temperature in the periphery of the sheet metals being joined. The high welding speed along with a relatively low heat input results in a minimal distortion of the sheet metal and marginal metallurgical changes in the parent material. In the steel specimens, this FCW implementation produces a fine grain microstructure, enhancing mechanical properties in the region of the weld. Aluminum and copper produced mean bond strengths of 77 and 69 pct to that of the parent material, respectively, whilst the steel demonstrated a strength of 98 pct. Using a wire offers the opportunity to use a higher-alloyed additional material and to precisely adjust the additional material volume appropriate for a given material alignment and thickness. 相似文献
15.
The 34CrMo4(AISI 4130)steel is extensively utilized in the compressed natural gas cylinders.Due to the importance of thermomechanical processing in the production of these cylinders,the dynamic recrystallization(DRX)characteristics of 34CrMo4 steel were investigated.The effect of hot deformation parameters such as temperature and strain rate on the dynamic restoration processes of a 34CrMo4 alloy was studied.Hot compression tests were performed in the temperature range of 900 to 1100 ℃ and the strain rate r... 相似文献
16.
N. N. Popov T. I. Sysoeva S. D. Prokoshkin V. F. Lar’kin I. I. Vedernikova 《Russian Metallurgy (Metally)》2007,(4):310-316
The effects of the strain, the strain rate, the deformation temperature, the type of heat treatment, and the chemical composition on the mechanical properties of Ti-Ni-Nb shape memory alloys and the development of reactive stresses in them have been studied. The chemical composition and deformation temperature are shown to affect the mechanical properties of the alloys. The temperature-deformation conditions of reaching the maximum level of reactive stresses in the alloys are determined. The maximum reactive stress is found to depend on the mechanical properties of austenite, namely, on its yield strength. The best Ti-Ni-Nb alloy compositions are chosen for use in thermomechanical joints in pipelines. 相似文献
17.
ZHU Miao-yong WANG Jun ZHANG Ying 《钢铁研究学报(英文版)》2005,12(6):14-19
SymbolList Ab,An———Surfaceareaofbroadfaceandnarrowfaceof moldrespectively,m2;Cp———Effectiveheatcapacity,J·kg-1·K-1;Cp,s———Heatcapacityofsolidphase,J·kg-1·K-1;Cp,l———Heatcapacityofliquidphase,J·kg-1·K-1;Cw———Waterheatcapacity,J·kg-1· 相似文献
18.
R. R. Hart B. C. Wonsiewicz G. Y. Chin 《Metallurgical and Materials Transactions B》1970,1(11):3163-3172
A thermomechanical processing technique for in creasing the strength of copper alloys is described. Alloys studied include phosphor bronze (5 pct Sn), nickel silver (12 pct Ni-28 pct Zn), tin-modified cupronickel (9 pct Ni-2 pctSn), and Cu?Be (2 pct Be). In this technique, the material is cold-rolled to about 95 pct reduction in thickness followed by heat treatment below the recrystallization temperature. The severe cold work results in increased strenght through strain hardening and texture strengthening, but at the expense of decreased ductility. The terminal heat treatment recovers the ductility while maintaining or increasing the strength imparted by cold work alone. Preliminary results indicate that cold work-accelerated precipitation is chiefly responsible for the strength increase during heat treatment. As a result of the present processing, the copper alloys exhibit higher yield strengths for given amounts of ductility than have heretofore been attained. 相似文献
19.
Turbulent Fluid Flow Phenomena in a Water Model of an AOD System 总被引:1,自引:0,他引:1
Experimental measurements are reported regarding fluid flow and turbulence property measurements in a water model of an AOD
vessel. Laser velocimetry was used to determine the time smoothed velocities, the turbulent kinetic energy, and the Reynolds
stresses in the system; in addition, the rate of melting of immersed ice rods was also measured to determine the local heat
transfer rates. The measurements have shown that for the model AOD studied both the velocity fields and the distribution of
the turbulent kinetic energy were quite uniform; the absence of inactive or dead zones would render these systems ideal for
mixing and for a range of ladle metallurgical operations. The rate at which immersed ice rods dissolved depended on both the
local velocities and on the turbulence levels; a previously developed correlation could be employed to predict the appropriate
heat transfer coefficients. Finally, the rate of turbulent energy dissipation per unit volume in real industrial AOD vessels
was found to be much higher than in any other ladle metallurgy operations. This could raise interesting possibilities regarding
the more widespread use of these systems for molten metals processing. 相似文献
20.
The occurrence of shear bands in nonisothermal, hot forging of Ti-6Al-2Sn-4Zr-2Mo-0. ISi (Ti-6242) was investigated in order to establish the material properties and process parameters which generally lead to shear bands and shear cracks in conventional hot forging of metals. Upset compression tests on cylindrical samples and lateral sidepressing tests on long, round bars were performed to determine the modes by which flow localizes in deformation states ranging from axisymmetric to plane strain. In axisymmetric deformation, it was found that nonisothermal, hot compression leads to chill zones and bands of intense deformation separating the chill zones from the deforming bulk. For plane strain deformation, shear bands were found to initiate along zero extension directions and subsequently localize flow in a manner analogous to the formation and propagation of shear bands in isothermal, hot forging. For both deformation states, it was found that material properties, such as the flow stress dependence on temperature, and process parameters, such as forging speed and die temperature which strongly influence the amount of heat transfer, play critical roles in the flow localization process. A simple model quantifying these effects was developed to predict the occurrence and severity of the shear bands observed in the Ti-6242 alloy hot forged at various temperatures and rates. In addition, the occurrence of shear cracking under certain forging conditions was rationalized in terms of the chilling brought about by nonisothermal, hot forging conditions and the inferior workability of Ti-6242 at temperatures far below the transus temperature. 相似文献