共查询到20条相似文献,搜索用时 31 毫秒
1.
P. Bala Srinivasan 《国际钢铁研究》2008,79(10):806-808
Laser welding of AISI 410 martensitic stainless steel was attempted in a diffusion cooled RF excited CO2 slab laser under Gaussian mode with argon and nitrogen as shielding gas. The effect of shielding gas and energy density on the resultant weld bead geometry, microstructure and hardness were assessed and discussed. It has been observed that welds obtained under nitrogen shielding conditions had higher and uniform hardness across the weld metal on account of reduced ferrite content. 相似文献
2.
The effects of shielding gas and post weld heat treatment on the pitting resistance, stress corrosion cracking and hydrogen embrittlement of supermartensitic stainless steel deposits were studied. Two all-weld-metal test coupons were prepared using a metal-cored wire under Ar+5% He and Ar+18%CO2 gas shielding mixtures. Solubilizing and solubilizing plus double tempering heat treatments were done with the objective of achieving different microstructural results. The samples welded under Ar+5% He showed higher pitting corrosion resistance, for all post weld heat treatments, than those welded under Ar+18%CO2. The different post weld heat treatments generated higher susceptibility to this corrosion mechanism. None of the samples presented signs of stress corrosion cracking, but in those subjected to the heat treatment, grain boundary selective attack was observed, on the surfaces of all the samples studied. The samples with highest hardness were more susceptible to hydrogen damage, thereby leading to reduced tensile strength on this condition. 相似文献
3.
Laser butt welds were fabricated in a titanium alloy (Ti-6A1-4V, AMS 4911-Tal0 BSS, annealed) using a Control Laser 2 kW CW
CO2 laser. The relationships between the weld microstructure and mechanical properties are described and compared to the theoretical
thermal history of the weld zone as calculated from a three-dimensional heat transfer model of the process. The structure
of the weld zone was examined by radiography to detect any gross porosity as well as by both optical and electron microscopy
in order to identify the microstructure. The oxygen pick-up during gas shielded laser welding was analyzed to correlate further
with the observed mechanical properties. It was found that optimally fabricated laser welds have a very good combination of
weld microstructure and mechanical properties, ranking this process as one which can produce high quality welds. 相似文献
4.
Shanping Lu Hidetoshi Fujii Kiyoshi Nogi 《Metallurgical and Materials Transactions A》2004,35(9):2861-2867
Small CO2 additions of 0.092 to 10 vol pct to the Ar shielding gas dramatically change the weld shape and penetration from a shallow
flat-bottomed shape, to a deep cylindrical shape, to a shallow concave-bottomed shape, and back to the shallow flat-bottomed
shape again with increasing CO2 additions in gas thermal arc (GTA) welding of a SUS304 plate. Oxygen from the decomposition of CO2 transfers and becomes an active solute element in the weld pool and reverses the Marangoni convection mode. An inward Marangoni
convection in the weld pool occurs when the oxygen content in the weld pool is over 80 ppm. Lower than 80 ppm, flow will change
to the outward direction. An oxide layer forms on the weld pool in the welding process. The heavy oxide layer on the liquid-pool
surface will inhibit the inward fluid flow under it and also affects the oxygen transfer to the liquid pool. A model is proposed
to illustrate the interaction between the CO2 gas and the molten pool in the welding process. 相似文献
5.
The effects of using oxygenated assist gases on the weldability and weld properties of Nd:YAG, pulsed laser welds in copper
(Cu) have been evaluated. It was found that the effective absorptivity of the Cu increased as the oxygen content of the Ar
assist gas was increased. This facilitated laser welding of Cu at much lower laser powers and increased weld penetration.
The use of oxygenated assist gas promoted nucleation and growth of submicroscopic oxide particles within the weld metal. These
particles dispersion-strengthened the weld metal, thereby increasing both weld metal hardness and strength. However, when
O2 concentrations in the assist gas were greater than 90 pct, weld metal embrittlement due to excessive volume fractions of
oxides was observed. The use of oxygenated assist gas also led to excessive cold lapping and poor bead quality. The bead quality
was improved, however, by ramping-down the laser power before terminating each pulse. 相似文献
6.
Wei Dong Hiroyuki Kokawa Yutaka S. Sato Susumu Tsukamoto 《Metallurgical and Materials Transactions B》2005,36(5):677-681
Nitrogen desorption by high-nitrogen steels (HNSs) containing 0.32 and 0.53 pct nitrogen during CO2 laser welding in an Ar-N2 gas mixture was investigated and the obtained data were compared with those for arc welding and at the equilibrium state
predicted by Sieverts’ Law. Although the nitrogen content in the weld metal during CO2 laser welding was lower than that in the as-received base material in all conditions, the nitrogen desorption was larger
in the top part of the weld metal than in the keyhole region. The nitrogen desorption in the Ar atmosphere was less during
CO2 laser welding than during arc welding. With the increase in nitrogen partial pressure, the nitrogen content in the weld metal
sharply increased during arc welding, but only slightly increased during CO2 laser welding. The nitrogen absorption and desorption of the HNS weld metal were much smaller during CO2 laser welding than during arc welding. 相似文献
7.
CO2 laser beam welding of 6061-T6 aluminum alloy thin plate 总被引:1,自引:0,他引:1
Akio Hirose Kojiro F. Kobayashi Hirotaka Todaka 《Metallurgical and Materials Transactions A》1997,28(12):2657-2662
Laser beam welding is an attractive welding process for age-hardened aluminum alloys, because its low heat input minimizes
the width of weld fusion and heat-affected zones (HAZs). In the present work, 1-mm-thick age-hardened Al-Mg-Si alloy, 6061-T6,
plates were welded with full penetration using a 2.5-kW CO2 laser. Fractions of porosity in the fusion zones were less than 0.05 pct in bead-on-plate welding and less than 0.2 pct in
butt welding with polishing the groove surface before welding. The width of a softened region in the-laser beam welds was
less than 1/4 times that of a tungsten inert gas (TIG) weld. The softened region is caused by reversion of strengthening β″
(Mg2Si) precipitates due to weld heat input. The hardness values of the softened region in the laser beam welds were almost fully
recovered to that of the base metal after an artificial aging treatment at 448 K for 28.8 ks without solution annealing, whereas
those in the TIG weld were not recovered in a partly reverted region. Both the bead-on-plate weld and the butt weld after
the postweld artificial aging treatment had almost equivalent tensile strengths to that of the base plate. 相似文献
8.
B. Chakrabarti H. Das S. Das T. K. Pal 《Transactions of the Indian Institute of Metals》2013,66(3):221-230
In recent years, weld cladding are being applied in numerous industries as cost effective engineering solution to use a surface protection layer to protect carbon steel against corrosion attack. The desirable characteristics of cladding alloy are reasonable strength, weldability, resistance to general and localized corrosion attack. The duplex stainless steel having all the desirable characteristic is the candidate material for cladding. However, duplex weld metals have not been studied in detail as duplex stainless steels. Consequently, the properties of duplex weld metals are less well known and only partially understood. In the present study, the properties of duplex weld deposits of the 22 % Cr, 10 % Ni, 3 % Mo, and 0.12 % N type using GMAW process have been investigated. In particular, the influence of welding heat input and shielding gas composition in GMAW process on weld deposit microstructure, impact toughness and resistance to pitting corrosion have been studied. It is observed that concentration of nitrogen of weld deposits influenced by both heat input and shielding gas composition exerted significant effect on microstructure, low temperature toughness and resistance to pitting corrosion. 相似文献
9.
Abdel-Monem El-Batahgy 《国际钢铁研究》1997,68(12):546-551
The weldability of Zn-coated steel sheets 0.7 mm thick was investigated using resistance spot welding process. The effect of welding current, welding time and holding time on weld nugget characteristics, microstructure, and mechanical properties was discussed. Then, the possibility of replacing this welding process with laser beam welding was outlined. In this respect, quality of weld joints as a function of zinc removal by grinding prior to welding was evaluated. It is found that resistance spot welding current and time are the most significant parameters in affecting both expulsion and Zn-induced porosity. Expulsion was avoided and Zn-induced porosity was reduced with the decrease in welding current and/or welding time. Zn-induced porosity was completely eliminated by zinc-removal by grinding prior to welding. The best weld joint concerning nugget characteristics, soundness and tensile shear strength was obtained using welding current of 10 kA, weld cycle of 20, holding cycle of 18. Unlike resistance spot welds, high quality of CO2 laser welds free from Zn-induced porosity could be made without zinc removal by grinding before welding. 相似文献
10.
This article discusses the effects of laser welding parameters such as power, welding speed, and focus position on the weld
bead profile, microstructure, pseudo-elasticity (PE), and shape memory effect (SME) of NiTi foil with thickness of 250 μm using 100W CW fiber laser. The parameter settings to produce the NiTi welds for analysis in this article were chosen from
a fractional factorial design to ensure the welds produced were free of any apparent defect. The welds obtained were mainly
of cellular dendrites with grain sizes ranging from 2.5 to 4.8 μm at the weld centerline. A small amount of Ni3Ti was found in the welds. The onset of transformation temperatures (A
s
and M
s
) of the NiTi welds shifted to the negative side as compared to the as-received NiTi alloy. Ultimate tensile stress of the
NiTi welds was comparable to the as-received NiTi alloy, but a little reduction in the pseudo-elastic property was noted.
Full penetration welds with desirable weld bead profiles and mechanical properties were successfully obtained in this study. 相似文献
11.
Wei Dong Hiroyuki Kokawa Yutaka S. Sato Susumu Tsukamoto 《Metallurgical and Materials Transactions B》2003,34(1):75-82
Nitrogen absorption by iron, Fe-20Cr-10Ni alloy, and SUS329J1 duplex stainless steel during CO2 laser welding in an Ar-N2 gas mixture was investigated and compared with equilibrium data predicted on Sieverts’ law and data on absorption during
arc and YAG laser welding. The nitrogen absorption during CO2 laser welding is lower than that during arc welding, but higher than that during YAG laser welding. Compared with arc welding,
the lesser contact of monatomic nitrogen with the weld pool surface and the higher partial pressure of metal vapor in the
keyhole may result in the lower nitrogen absorption during CO2 laser welding, while the very low density of monatomic nitrogen in the atmosphere during YAG laser welding due to the low-temperature
plume may lead to the lower nitrogen absorption during YAG laser welding than during CO2 laser welding. 相似文献
12.
The effects of process variables on pulsed Nd:YAG laser spot welds: Part I. AISI 409 stainless steel
The weldabilities of AA 1100 aluminum and AISI 409 stainless steel by the pulsed Nd:YAG laser welding process have been examined
experimentally and compared. The effects of Nd:YAG laser welding parameters, including laser pulse time and power intensity,
and material-dependent variables, such as absorptivity and thermophysical properties, on laser spot-weld characteristics,
such as weld diameter, penetration, melt area, melting ratio, porosity, and sur-face cratering, have been studied experimentally.
The results of this work are reported in two parts. In Part I, the weldability of AISI 409 stainless steel by the pulse laser
welding process is reported. In Part II, the weldability of A A 1100 aluminum under the same operating con-ditions is reported
and compared to those of the stainless steel. When welding AISI 409 stainless steel, weld pool shapes were found to be influenced
most by the power intensity of the laser beam and to a lesser extent by the pulse duration. Conduction mode welding, keyhole
mode welding, and drilling were observed. Conduction mode welds were produced when power in-tensities between 0.7 and 4 GW/m2 were used. The initial transient in weld pool development occurred in the first 4 ms of the laser pulse. Following this,
steady-state conditions existed and conduction mode welds with aspect ratios (depth/width) of about 0.4 were produced. Keyhole
mode welds were observed at power intensities greater than 4 GW/m2. Penetration of these keyhole mode welds increased with increases in both power intensity and pulse time. The major weld
defects observed in the stainless steel spot welds were cratering and large-occluded gas pores. Significant metal loss due
to spatter was measured during the initial 2 ms of keyhole mode welds. With increasing power intensity, there was an increased
propensity for occluded gas pores near the bottom of the keyhole mode welds.
Formerly Graduate Student. 相似文献
13.
Christian B. Fuller Murray W. Mahoney 《Metallurgical and Materials Transactions A》2006,37(12):3605-3615
Friction stir processing (FSP) is used locally to modify the microstructure and thus mechanical properties of 5083-H321/5356
aluminum gas metal arc welds (GMAWs). Four specimen approaches were examined: as-arc welded, weld toe FSP (with arc weld on
either the advancing or the retreating side of tool), and weld crown FSP. Microstructures within the fine-grained FSP region
contained smaller constituent particles. Mg2Si and Al6(Fe,Mn), than those particles found in the arc weld nugget, heat-affected zone (HAZ), and base-metal (BM) locations. The FSP
improved the monotonic tensile strength, yield strength, and elongation of 5083-H321/5356 Al arc welds by 6 to 9 pct, 7 to
13 pct, and 46 to 80 pct, respectively. The addition of FSP produced a 30 pct increase in the load necessary to reach 107 cycles during four-point bending fatigue. An analysis of strengthening mechanisms determined that solid-solution, grain-size,
and precipitation strengthening made contributions to the calculated yield strength of the BM, are weld nugget, and FSP regions.
In addition, the strength mechanism analysis demonstrated that FSP increased the amount of grain-size strengthening and precipitate
strengthening by nearly 110 MPa, when compared to the arc weld nugget. 相似文献
14.
Gandham Phanikumar Sambandam Manjini Pradip Dutta Kamanio Chattopadhyay Jyotirmoy Mazumder 《Metallurgical and Materials Transactions A》2005,36(8):2137-2147
Continuous CO2 laser welding of an Fe-Cu dissimilar couple in a butt-weld geometry at different process conditions is studied. The process
conditions are varied to identify and characterize the microstructural features that are independent of the welding mode.
The study presents a characterization of the microstructure and mechanical properties of the welds. Detailed microstructural
analysis of the weld/base-metal interface shows features that are different on the two sides of the weld. The iron side can
grow into the weld with a local change in length scale, whereas the interface on the copper side indicates a barrier to growth.
The interface is jagged, and a banded microstructure consisting of iron-rich layers could be observed next to the weld/Cu
interface. The observations suggest that solidification initiates inside the melt, where iron and copper are mixed due to
convective flow. The transmission electron microscopy (TEM) of the weld region also indicates the occasional presence of droplets
of iron and copper. The microstructural observations are rationalized using arguments drawn from a thermodynamic analysis
of the Fe-Cu system. 相似文献
15.
Bharat K. Jasthi William J. Arbegast Stanley M. Howard 《Metallurgical and Materials Transactions A》2012,43(9):3192-3201
The effect of thermal aging on the corrosion and microstructure of friction-stir welded (FSW) alloy 22 was investigated. Successful welds were produced with a polycrystalline cubic BN pin tool at a rotational speed of 200 rev min?1 and travel speed of 12.7 mm min?1. Topologically closed packed (TCP) phases of ~50 to 300 nm size were identified in the weld nugget. The area fraction of the TCP phases in the weld nugget increased with aging temperature and time. General corrosion rates measured from the weight loss experiments for welds were relatively higher than for parent material. The corrosion rates increased with the increased aging temperature and time. Intergranular corrosion (IGC) resistance is greater in friction-stir welds compared with the parent material at all aging temperatures and times. The IGC depth increased with the aging temperature and time in the parent material. The IGC depth for the FSW weld nugget was minimal and did not change with thermal aging. 相似文献
16.
Shengyong Pang Weidong Chen Wen Wang 《Metallurgical and Materials Transactions A》2014,45(6):2808-2818
Quantitative prediction of the porosity defects in deep penetration laser welding has generally been considered as a very challenging task. In this study, a quantitative model of porosity defects induced by keyhole instability in partial penetration CO2 laser welding of a titanium alloy is proposed. The three-dimensional keyhole instability, weld pool dynamics, and pore formation are determined by direct numerical simulation, and the results are compared to prior experimental results. It is shown that the simulated keyhole depth fluctuations could represent the variation trends in the number and average size of pores for the studied process conditions. Moreover, it is found that it is possible to use the predicted keyhole depth fluctuations as a quantitative measure of the average size of porosity. The results also suggest that due to the shadowing effect of keyhole wall humps, the rapid cooling of the surface of the keyhole tip before keyhole collapse could lead to a substantial decrease in vapor pressure inside the keyhole tip, which is suggested to be the mechanism by which shielding gas enters into the porosity. 相似文献
17.
The corrosion behaviour of weld metal, partially melted zones and heat affected zones of gas tungsten arc welds in A356 Al-Si
alloy with different prior thermal tempers has been studied. Continuous and pulsed current gas tungsten arc welding techniques
were used. Potentiodynamic polarization testing was carried out to determine the corrosion resistance. Optical and scanning
electron microscopy studies were carried out to determine the corrosion mechanism. The partially melted zone of the welds
was found to be attacked severely. A pulsing technique was found to decrease the severity of corrosion damage in the partially
melted zone. The prior thermal condition of the alloys was found to influence the corrosion of heat affected zones of welds. 相似文献
18.
Sheikh A. Rezan Guangqing Zhang Oleg Ostrovski 《Metallurgical and Materials Transactions B》2012,43(1):73-81
This article examined the reduction/nitridation of rutile in the He-N2, Ar-N2, and He (Ar)-H2-N2 gas mixtures, as well as pure nitrogen, in the temperature-programmed and isothermal experiments in a fixed-bed reactor.
The extents of reduction and nitridation were determined from the off gas composition and LECO analysis. The off-gas composition
was monitored using the infrared sensor (CO, CO2, and CH4) and dew point analyzer (H2O). The phase composition of the reduced samples was analyzed using X-ray diffraction (XRD). The temperature and gas composition
had a strong effect on the rutile reduction. The reduction was the fastest in the H2-N2 gas mixture, followed by a reduction in nitrogen; the rate of reduction/nitridation in the He-N2 gas mixture was marginally higher than in the Ar-N2 gas. The rate of titania reduction/nitridation in the He (Ar)-H2-N2 gas increased with the replacement of He (Ar) with hydrogen. The article also discusses the mechanisms of reduction/nitridation
in different gas atmospheres. 相似文献
19.
The laser surface cladding technique was used to formin situ Fe-Cr-Mn-C alloys on AISI 1016 steel substrate. In this process mixed powders containing Cr, Mn, and C with a ratio of 10∶1∶1
were delivered using a screw feed, gravity flow carrier gas aided system into the melt pool generated by a 10 kw CO2 laser. This technique produced ultrafine microstructure in the clad alloy. The microstructure of the laser surface clad region
was investigated by optical, scanning, and transmission electron microscopy and X-ray microanalysis techniques. Microstructural
study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced
a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy
of this composition does not show any martensitic or retained austenite phase. In preliminary wear studies the laser clad
Fe-Cr-Mn-C alloys exhibited far superior wear properties compared to Stellite 6 during block-on-cylinder tests. The improved
wear resistance is attributed to the fine distribution of metastable M6C carbides. 相似文献
20.
In this two-part article, the weldabilities of AA 1100 aluminum and AISI 409 stainless steel by the pulsed Nd:YAG laser welding
process have been examined experimentally and compared. The effects of laser pulse time and power density on laser spot weld
characteristics, such as weld diameter, penetration, melt area, melting ratio, porosity, and surface cratering, have been
studied and explained qualitatively in relation to material-dependent variables such as absorptivity and thermophysical properties.
The weldability of AISI 409 stainless steel was reported in Part I of this article. In the present article, the weldability
of AA 1100 aluminum is reported and compared to that of AISI 409 stainless steel. Weld pool shapes in aluminum were found
to be influenced by the mean power density of the laser beam and the laser pulse time. Both conduction-mode and keyhole-mode
welding were observed in aluminum. Unlike stainless steel, however, drilling was not observed. Conduction-mode welds were
produced in aluminum at power densities ranging from 3.2 to 10 GW/m2. The power density required for melting aluminum was approximately 4.5 times greater than stainless steel. The initial transient
in weld pool development in aluminum occurred within 2 ms, and the aspect ratios (depth/width) of the steady-state conduction-mode
weld pools were approximately 0.2. These values are about half those observed in stainless steel. The transition from conduction-
to keyhole-mode welding occurred in aluminum at a power density of about 10 GW/m2, compared to about 4 GW/m2 for stainless steel. Weld defects such as porosity and cratering were observed in both aluminum and stainless steel spot
welds. In both materials, there was an increased propensity for large occluded vapor pores near the root of keyhole-mode welds
with increasing power density. In aluminum, pores were observed close to the fusion boundary. These could be eliminated by
surface milling and vacuum annealing the specimens, suggesting that such pores were due to hydrogen. Finally, excellent agreement
was obtained between experimental data from both alloys and an existing analytical model for conduction-mode laser spot welding.
Two nondimensional parameters, the Fourier number and a nondimensional incident heat flux parameter, were derived and shown
to completely characterize weld pool development in conduction-mode welds made in both materials. 相似文献