A new method--the inverse strain method(ISM)for preventing welding hot cracking of high strength aluminium alloy LY12CZ

In this paper a new method for preventing welding hot cracking—the inverse strain method(ISM)is developed on the principle of welding mechan- ics.Effectiveness and feasiblity of method in preventing welding hot cracking of high strength aluminum alloy LY12CZ by synchronous rolling during welding (SRDW)along both sides of the weld at a suitable distance behind the welding arc are examined.Experimental resulte indicate that welding hot cracking of LY12CY can be effectively prevented and the mechanical properties of welded joint can also be improved by the method.It is an important new solution for preventing hot cracking in welding of sheet metal.

Influence of prior austenite grain size on the critical strain for completion of DEFT through hot compression test

A low carbon steel was used to determine the critical strain εc for completion of deformation enhanced ferrite transformation （DEFT） through a series of hot compression tests. In addition, the influence of prior austenite grain size （PAGS） on the critical strain was systematically investigated. Experimental results showed that the critical strain is affected by PAGS. When γ→α transformation completes, the smaller the PAGS is, the smaller the critical strain is. The ferrite grains obtained through DEFT can be refined to about 3 μm when the DEFT is completed.

Effects of Strain Rate on Dislocation for TA15 Alloy during Hot Compressive Deformation

The effects of strain rate on the dislocation type and dislocation configure of TA15 alloy were investigated.The experimental results show that the operating dislocation type changes from c type to c and a＋ c type with increasing strain rate under the deformation condition of 900℃,60% strain.Under the condition of 900℃,60% strain and 0.001/s strain rate,lots of orientate dislocation cellular configurations and sub-grains,many dislocations pile up before sub boundary.When the strain rate increases to 0.1/s,some dislocations exhibit curved and dislocation tangles and pile-ups can be found,suggesting more dislocations and much stronger interactions among dislocations.

EFFECTS OF STRAIN RATE & TEMPERATURE ON HOT COMPRESSION FLOW BEHAVIOR OF A HYDROGENATED CAST Ti-25Al-10Nb-3V-1Mo ALLOY

The flow behavior of a cast Ti-25Al-10Nb-3V-1Mo alloy based onTi3Al, with and without hydrogen content, was investigated under isothermal compression test at strain rates of 0.1s-1 to 0.001s -1 in the temperature range of 900℃ to1000 ℃. The hot compression peak stress (or the maximum flow stress) of the alloy withand without hydrogen decreases with the increasing temperature and the decreasingstrain rate. Hydrogenation makes the hot compression peak stress decrease by 37%～53%, which corresponds to lowering the deformation temperature by about 50℃.Strain rate does not change the favorable effect of hydrogenation on hot compressionflow behavior at all three deformation temperatures. The microstructure of the alloywith 0.2% H (mass %) deformed at a fixed temperature exhibits the same feature asthat of the alloys without hydrogenation deformed at higher temperatures for bothstrain rates. Hydrogenation has the same effect on microstructure as strain rate andtemperature.

Effect of Hot Carrier on Amplitude Modulation and Demodulation of Gaussian High Power Helicon Wave in Homogeneous Longitudinally Magnetized Strain Dependent Dielectric Material

In the present communication, the hydrodynamic model is used to investigate the amplitude modulation as well as demodulation of an electromagnetic wave of high power helicon pump wave into another helicon wave in strain dependent dielectric material incorporating carrier heating (CH) effects. The consideration of CH in modulation and demodulation is prime importance for the adding of new dimension in analysis of amplification of acoustic helicon wave. By using the dispersion relation, threshold pump electric filed and growth rate of unstable mode from the modulation and demodulation of the high power helicon wave well above from the threshold value will be discussed in the present analysis. The numerical analysis is applied to a strain dependent dielectric material, BaTiO3 at room temperature and irradiated with high power helicon wave of frequency 1.78 × 1014 Hz. This material is very sensitive to the pump intensities, therefore during studies, Gaussian shape of the helicon pump wave is considered during the propagation in stain dependent dielectric material and opto-acoustic wave in the form of Gaussian profile (ω0,κ0) is induced longitudinally along the crystallographic plane of BaTiO3. Its variation is caused by the available magnetic field (ωc), interaction length (z) and pulsed duration of interaction (τ). From the analysis of numerical results, the incorporation of CH effect can effectively modify the magnitude of modulation or demodulation of the amplitude of high power helicon laser wave through diffusion process. Not only the amplitude modulation and demodulation of the wave, the diffusion of the CH effectively modifies the growth rate of unstable mode of frequency in BaTiO3. The propagation of the threshold electric field shows the sinusoidal or complete Gaussian profile, whereas this profile is found to be completely lost in growth of unstable mode. It has also been seen that the growth rate is observed to be of the order of 108 - 1010 s-1 but from diffusion of carrier heating, and that its order is enhanced from 1010 - 1012 s-1 with the variation of the magnetized frequency from 1 to 2.5 × 1014 Hz.

Evaluating location specific strain rates, temperatures,and accumulated strains in friction welds through microstructure modeling

A microstructural simulation method is adopted to predict the location specific strain rates, temperatures, grain evolution, and accumulated strains in the Inconel 718 friction welds. Cellular automata based 2D microstructure model was developed for Inconel 718 alloy using theoretical aspects of dynamic recrystallization. Flow curves were simulated and compared with experimental results using hot deformation parameter obtained from literature work. Using validated model, simulations were performed for friction welds of Inconel 718 alloy generated at three rotational speed i.e., 1200, 1500, and1500 RPM. Results showed the increase in strain rates with increasing rotational speed. These simulated strain rates were found to match with the analytical results. Temperature difference of 150 K was noticed from center to edge of the weld. At all the rotational speeds, the temperature was identical implying steady state temperature(0.89 T_m) attainment.

Influence of hot rolling on the microstructure of lean duplex stainless steel 2101

In this work, the microstructure and the strain partitioning of lean duplex stainless steel 2101 (LDX 2101) during different hot-rolling processes are investigated by optical microscopy and electron-backscattered diffraction (EBSD). The results show that the LDX 2101 exhibits poor thermoplasticity at high temperature. The four-pass hot-rolled plates show fewer edge-cracking defects and superior thermoplasticity compared with the two-pass hot-rolled plates prepared at different temperature. The phase boundary is the weakest site in the LDX 2101. The cracks are initiated and propagated along the phase boundaries during the hot-rolling process. According to the EBSD analysis, the increase of the hot-rolling pass can dramatically improve the strain distribution in ferrite and austenite phases and promote the strain transmission in the constituent phases, thereby improving the coordinated deformation ability of the two phases. This effect further in- creases the thermoplasticity and reduces the formation of edge cracks in LDX 2101.

Effect of Strain Rate on the Ferrite Grain Refinement in a Low Carbon Nb-Ti Microalloyed Steel during Low Temperature Deformation

Grain refinement is one of the effective methods to develop new generation low carbon microalloyed steels possessing excellent combination of mechanical properties. The microstructural evolution and ferrite grain refinement at the deformation temperature of 865℃, above Ar3, with different strain rates were investigated using single pass isothermal hot compression experiments for a low carbon Nb-Ti microalloyed steel. The physical processes that occurred during deformation were discussed by observing the optical microstructure and analyzing the true stress-true strain responses. At strain rates of 0.001 and 0.01s^-1, there is no evidence of work hardening behavior during hot deformation and strain-induced transformation （SIT） leads to dynamic flow softening in flow curves. Optical microscopy observation shows that ultrafine and equiaxed ferrite with grain sizes of 2μm can be obtained by applying deformation with strain rate of 0.1 s^-1 due to SIT just after deformation. Furthermore, increasing the strain rate from 0.001 to 0.1 s^-1 reduces both the grain size of the equiaxed ferrite and the amount of deformed ferrite.

STUDY ON THE HOT DEFORMATION BEHAVIORS OF Al-Zn-Mg-Cu-Cr ALUMINUM ALLOY

The hot deformation behaviors and microstructures of A1-Zn-Mg-Cu-Cr aluminum alloy have been studied using thermal simulation test, optical microscopy and transmission electron microscopy. As a result, the true stress versus true strain curves and the microstructures under various deformation conditions are obtained. The microstructures gradually incline to dynamic-recrystallization with the deformation temperature rising and the recrystallization grains refine with the decrease of deformation temperature or with raising the strain rates. The quantitative relationship between the Zener-Hollomon parameter （Z） and average recrystallization grain size in the subsequent heat treatment is set up.

FEM analysis for hot rolling process of AM60 alloy

<正>The rolling of AM60 sheets for 50%reduction was analyzed with DEFORM to investigate the hot deformation process. The simulated results show that the sheet velocities at the entrance(21 mm/s) and at the exit(37 mm/s) are less and larger than roll velocity,respectively.From the entrance to the neutral point,the velocity at the sheet surface is greater than that at the middle point of sheet in thickness,while that from the neutral point to the exit shows the opposite pattern.The effective strain of the sheet increases from the entrance to the exit due to the continuous reduction in thickness.In addition,the effective strain at the sheet surface reaches to 1.0 and is larger than that of 0.8 at the middle point of sheet.The difference of effective strain in thickness direction has a much stronger effect on the recrystallized fraction than on the recrystallized grain size.The minimum temperature of 347℃is obtained at the surface contacting directly with roll and the maximum temperature 388℃at the middle point of sheet in thickness.

Anisotropy of Superplasticity in Hot-rolled Sheet of Ti-10V-2Fe-3Al

A superplastic tension test was carried out in order to examine the anisotropy of superplasticity in hot rolled sheet of Ti-10V-2Fe-3Al. Flow stress in the longitudinal (L) direction is higher than that in the transverse (T) direction of the sheet. The peak value of elongation in L direction specimens is also higher within a strain rate range of 0.0005-0.0083/s. Based on microstructure changes before and after superplastically deformation, an analysis is made for multi-necking on the T specimen after tension. The flowlines in superplastically deformed specimen are described.

Effect of strain rate on solidification crack susceptibility of different metals

In this paper,a slow bending speed varestraint test method with con- tinuously adjustable deformation rate for testing hot cracking sensitivity is de- veloped and its working principle is described.From great amounts of tests,it is known that strain rate affects the sensitivity of solidification crack because of its influnce on material ductility in BTR directly.The smaller the strain rate, the better the ductility and the lower the solidification crack sensitivity.The ex- tent of this effect varies with different materials,for LF-6 aluminum alloy,it is great,but for 16Mn,19Mn5 and 20G steels,it is small.Through systematic investigation,it is concluded that strain rate of a metal during welding can be lowered and the resistance to solidification crack can be enhanced by reducing structrual restraint and by adjustment of welding parameters.

EFFECT OF AUSTEMPERING ON TRANSFORMATION INDUCED PLASTICITY OF HOT ROLLED MULTIPHASE STEELS

Effect of austempering on the transformation induced plasticity （TRIP） of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could be obtained in the hot rolled multiphase steel. Strain induced martensite transformation （SIMT） of retained austenite and TRIP effectively occur under straining owing to austempering after hot rolling, and mechanical properties of the present steel remain at a relatively high constant value for austempering at 400℃. The mechanical properties of the steel exhibited a good combination of tensile strength （791MPa） and total elongation （36%） because the stability of retained austenite is optimal when the steel is held for 20min.

Transverse stress-strain evolution during welding of thin aluminum alloy plate

The FE simulation results of transverse stresses and strains during welding of thin aluminum alloy plate are presented. The results indicate that restraint condition is the main factor that determines whether or not hot cracking will occur. With rigid restraint hot cracking (crater cracking) will occur at the arc-stopping end, and such cracking usually will not occur without external restraint. But under restraint-free condition it is easy for terminal cracks to occur.

Prediction of Rolling Load, Recrystallization Kinetics, and Microstructure During Hot Strip Rolling

The recrystallization kinetics and grain size models were developed for the C Mn and niobium containing steels to describe the metallurgical phenomenon such as softening, grain growth, and strain accumulation. Based on the recrystallization kinetics equations, the mean flow stress and the rolling load of each pass were predicted and the optimum rolling schedule was proposed for hot strip rolling. The austenite grain refinement is associated with the addition of niobium, the decrease of starting temperature of finish rolling, and the reduction of finished thickness. The mean flow stress curve with a continuous rising characteristic can be usually observed in the finish rolling of niobium containing steel, which is formed as a result of the heavy incomplete softening and strain accumulation. The predic ted rolling loads are in good agreement with the measured ones.

Experimental research on hot-tearing crack sensitivity

Hot-tearing cracks usually form near the solidus temperature. It is caused by a combination of tensile stress and metallurgical embrittlement. In order to quantify embrittlement and to incorporate it in the thermal-stress analysis, many different criteria have been developed. Among them,the submerged split-chill tensile （SSCT） test is an efficient one. This paper tries to use SSCT to estimate the critical strain of hot tearing for some steels.

Study of the Effect of Hot－pressing Techniques on the Magnetic Properties of Pr－Fe－B Alloys

The effect of hot-pressing techniques on the magnetic properties of Pr-Fe-B alloys has been studied in this paper. The results show that the main factors influencing the magnetic properties for hot-pressing magnet are hot-pressing temperature, thickness reduction and strain rates. When the hot-pressing temperature is 800℃ and thickness reduction is 75%, the best magnetic properties are obtained as Br = 1.04 T, iHc = 1016 kA/m,(BH)max=201 kJ/m3.

Precise calculation of average strain and average strain rate considering roll elastic flattening

Considering roll elastic flattening, new equations were proposed to calculate the average strain ε and average strain rate ε- in the hot strip rolling process. By comparing the proposed equations with currently used equations ,it was observed that the strain rate of thick strip and strain are not sensitive to roll elastic flattening. However,for thin strip, a noticeable calculated difference in the strain rate occurred when roll elastic flattening was considered.

DYNAMIC MECHANICAL BEHAVIOURS OF HIGH Mo AUSTENITIC STAINLESS STEEL DURING HOT DEFORMATION

The dynamic mechanical behaviours of super low carbon high Mo austenitic stainless steel (00Cr20Nil8Mo6CuN)during hot deformation have been studied by using Formaster-Press hot working simulator. The hot deformation equation, as well as the relationship between peak strain, peak stress and Zener-Hollman parameter, together with the deformation activation energy have been resulted through the experiments.

含钪超高强铝合金在应变速率10^(-3)s^(-1)下的热流变及动态再结晶行为

采用等温热压缩实验和电子背散射衍射分析技术,研究了Al-11.1Zn-2.3Mg-2.0Cu-0.05Sc合金在应变速率10^(-3)s^(-1),变形温度653~733 K条件下的热流变及动态再结晶行为,建立动态再结晶临界应力、临界应变、相对含量、晶粒平均尺寸的拟合方程。结果表明:相关特征参数的拟合方程可以较好地描述含钪铝合金在实验条件范围内的动态再结晶行为。变形温度的升高会增加晶粒内部的取向差,减弱晶粒沿法向的择优取向,有助于动态再结晶的发生。动态回复是含钪铝合金的主要软化机制。随着温度的变化,铝合金微观组织存在不连续动态、连续动态及几何动态三种再结晶机制。