Effect of thermo-mechanical treatment on microstructure and mechanical properties of wire-arc additively manufactured Al-Cu alloy

Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolling and thermo-mechanical heat treatment(T8)with pre-stretching deformation between solution and aging treatment were adopted in this study.Their effects on hardness,mechanical properties and microstructure were analyzed and compared to the conventional heat treatment(T6).The results show that cold rolling increases the hardness and strengths,which further increase with T8 treatment.The ultimate tensile strength(UTS)of 513 MPa and yield stress(YS)of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment,which is much higher than that in the as-deposited samples.The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling;while both the T6 and T8 treatments decrease the elongation.The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitatedθ′phases,which inhibits the dislocation movement and enhances the strengths;as a result,T8 treatment shows better strengthening effect than the T6 treatment.The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.

Time-dependent effects in transient liquid phase bonding of 304L and Cp-Ti using an Ag-Cu interlayer

One of the challenges for bimetal manufacturing is the joining process.Hence,transient liquid phase(TLP)bonding was performed between 304L stainless steel and Cp-Ti using an Ag-Cu interlayer with a thickness of 75μm for bonding time of 20,40,60,and 90 min.The bonding temperature of 860℃ was considered,which is under the β transus temperature of Cp-Ti.During TLP bonding,various intermetallic compounds(IMCs),including Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe),Ti_(2)(Cu,Ag),and Ti_(2)Cu from 304L toward Cp-Ti formed in the joint.Also,on the one side,with the increase in time,further diffusion of elements decreases the blocky IMCs such as Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe)in the 304L diffusion-affected zone(DAZ)and reaction zone,and on the other side,Ti_(2)(Cu,Ag)IMC transformed into fine morphology toward Cp-Ti DAZ.The microhardness test also demonstrated that the(Cr,Fe)_(2)Ti+Ti_(5)Cr_(7)Fe_(17) IMCs in the DAZ on the side of 304L have a hardness value of HV 564,making it the hardest phase.The maximum and minimum shear strength values are equal to 78.84 and 29.0 MPa,respectively.The cleavage pattern dominated fracture surfaces due to the formation of brittle phases in dissimilar joints.

《中小学英语真实任务教学实践论》作伪举要——《英语课程标准》任务型语言学习研究四题之后(下)

《中小学英语真实任务教学实践论》篡改乔姆斯基生成语言学"能力"观,歪曲斯基汉"任务的两个根本特征",炮制任务型语言教学"交际途径发展论"权威,虚构任务型语言教学"标志性人物",掩盖国外任务途径原理研究和任务型语言教学研究的真相,其作伪对国内第二语言习得研究和外语教学研究以及英语新课程标准改革构成了学术陷阱,造成了学术误导,成为学术研究谬误之源。

Effect of process parameters on microstructure and properties of AM50A magnesium alloy parts formed by double control forming

Effects of process parameters on microstructure and mechanical properties of the AM50A magnesium alloy components formed by double control forming （DCF） were investigated via a four-factor and four-level orthogonal experiment. The variable curves of DCF showed that the forging procedure was started in the following 35 ms after the injection procedure was completed. It was confirmed that the high-speed filling and high-pressure densifying were combined together in the DCF process. Better surface quality and higher mechanical properties were achieved in the components formed by DCF as compared to die casting （DC） due to the refined and uniform microstructure with a few defects or without defects. Injection speed affected more effectively the yield strength （YS）, ultimate tensile strength （UTS） and elongation as compared to pouring temperature, die temperature and forging force. But the pouring temperature had a more significant effect on hardness as compared to injection speed, die temperature and forging force. Pouring temperature of 675 ＆#176;C, injection speed of 2.7 m/s and forging force of 4000 kN except for die temperature were the optimal parameters for obtaining the highest YS, UTS, elongation and Vickers hardness. Die temperatures of 205, 195, 195 and 225 ＆#176;C were involved in achieving the highest YS, UTS, elongation and Vickers hardness, respectively. Obvious microporosity and microcracks were found on the fracture surface of the components formed by DC, deteriorating the mechanical properties. However, the tensile fracture morphology of the components formed by DCF was characterized by ductile fracture due to a large number of dimples and no defects, which was beneficial for improving the mechanical properties.

Mechanical properties and microstructures of Al alloy tensile samples produced by serpentine channel pouring rheo-diecasting process

An innovative one-step semi-solid processing technique of A356 Al alloy,the serpentine channel pouring rheo-diecasting process （SCRC）,was explored.The mechanical properties and microstructures of the tensile samples made by the SCRC technique were tested in the as-cast and T6 heat treatment conditions.The experimental results show that the as-cast ultimate tensile strength can reach about 250MPa and the elongation is 8.6%？13.2%.The ultimate tensile strength can increase approximately 30% higher than that of the as-cast one but there is some slight sacrifice of the plasticity after T6 heat treatment.Under these experimental conditions,the semi-solid A356 Al alloy slurry with primary α1（Al） grains,which have the shape factor of 0.78？0.89 and the grain diameter of 35？45μm,can be prepared by the serpentine channel pouring process.The primary α2（Al） grains are very fine during the secondary solidification stage.Compared with the conventional HPDC process,the SCRC process can improve the microstructures and mechanical properties of the tensile test samples.The advantages of the SCRC process include easily incorporating with an existing HPDC machine,cancelling the preservation and transportation process of the semi-solid alloy slurry,and a higher cost performance.

Effect of zirconium addition on microstructure and mechanical properties of Mg_(97)Y_2Zn_1 alloy

The effects of zirconium addition on the microstructure and mechanical properties of Mg97Y2Zn1 alloy were investigated.The microstructure of as-cast Mg97Y2Zn1 alloy is refined by the addition of zirconium.During the extrusion,the initial nucleation sites of the alloy are mainly original grain boundaries and secondary phase.The addition of zirconium could stimulate the DRX process because more grain boundaries are formed,which increases the dynamic recrystallization rate.Both the strength and elongation of the alloy are increased by the addition of zirconium.

Effects of T9I6 thermo-mechanical process on microstructure, mechanical properties and ballistic resistance of 2519A aluminum alloy

The effects of T916 thermo-mechanical process on microstructures, mechanical properties and ballistic resistance of 2519A aluminum alloy were investigated by optical microscopy （OM）, transmission electron microscopy （TEM）, tensile tests and ballistic resistance test. After T916 treatment, the yield strength, tensile strength and elongation rate of 2519A aluminum alloy reach 501 MPa, 540 MPa and 14%, respectively. And the ballistic limit velocity of 2519A-T916 alloy （30 mm in thickness） is 715 rn/s. The microstructure varies near the sidewalls of crater. The interrupted ageing contributes to these excellent properties of the alloy. During T916 process, the precipitation of Guinier Preston （GP） zone is finer and denser during the interrupted ageing, thus resulting in well precipitated strengthening phase.

Effects of process parameters on mechanical properties and microstructures of creep aged 2124 aluminum alloy

A series of tests were carried microstructures of 2124 aluminum alloy in increase of aging time, temperature and low-to-peak-to-low manner. No significant out to investigate the effects of process parameters on mechanical properties and creep aging process. The results show that creep strain and creep rate increase with the applied stress. The hardness of specimen varies with aging time and stress in a effect of temperature on hardness of material is seen in the range of 185-195 ℃. The optimum mechanical properties are obtained at the conditions of （200 MPa, 185 ℃, 8 h） as the result of the coexistence of strengthening S＂ and S＇ phases in the matrix by transmission electron microscopy （TEM）. TEM observation shows that applied stress promotes the formation and growth of precioitates and no obvious stress orientation effect is observed in the matrix.

Influence of high frequency vibration on microstructure and mechanical properties of TIG welding joints of AZ31 magnesium alloy

A device for superimposing vibration on workpiece in both horizontal and vertical directions during tungsten-arc inert gas （TIG） welding was developed, with maximum power output of 2 kW at frequency of 15 kHz. AZ31 sheets with thickness of I and 3 mm were used in the vibratory welding. Microstructures along with the mechanical properties of the weld joints under different vibrating conditions （vibration direction, vibration amplitude and groove angle） were examined. It is observed that the grain size in welding zone decreases remarkably with the application of vibration, while the amount of second phase β-Mg_17Al_12 within the zone decreases slightly; meanwhile, microhardness of the weld joints, macroscopic tensile strength and elongation of the weldment increase. Vibration, especially the one along vertical direction, has more impact on the performance of the thick weldments. Influence of vibration on mierostructure and mechanical properties of weldments is affected by wave energy transferring in the melt and depends on the processing and geometric parameters including amplitude and direction of vibration, thickness, and groove angles.

Microstructure and mechanical properties of (TiB+La_2O_3)/Ti composites heat treated at different temperatures

Near-α titanium matrix composites reinforced with TiB and La2O3 were synthesized by common casting and hot-working technology.The effects of β heat treatment temperature on the microstructure and the tensile properties of the in situ synthesized（TiB＋La2O3）/Ti were studied.Microstructure was studied by OM and TEM,and tensile tests were carried out at room temperature and 923 K,respectively.Results show that with the increase of β heat treatment temperature,prior β phase grain size increases and αcolony size decreases.Room temperature tensile strength increases with the increase of β heat treatment temperature,which can be attributed to the decrease of α colony size with the increase of β heat treatment temperature.However,high-temperature tensile strength decreases with the increase of β heat treatment temperature and the decrease of the high-temperature tensile strength is due to the increase of the prior β phase grain size.

Dynamic mechanical properties and constitutive equations of 2519A aluminum alloy

To analyze the effects of strain rate and temperature on the flow stress of 2519A aluminum alloy, the dynamic mechanical properties of 2519A aluminum alloy were measured by dynamic impact tests and quasi-static tensile tests. The effects of strain rate and temperature on the microstructure evolution were investigated by optical microscopy （OM） and transmission electron microscopy （TEM）. The experimental results indicate that 2519A aluminum alloy exhibits strain-rate dependence and temperature susceptibility under dynamic impact. The constitutive constants for Johnson--Cook material model were determined by the quasi-static tests and Hopkinson bar experiments using the methods of variable separation and nonlinear fitting. The constitutive equation seems to be consistent with the experimental results, which provides reference for mechanical characteristics and numerical simulation of ballistic performance.

Influence of aging on microstructure and mechanical properties of AZ80 and ZK60 magnesium alloys

The effect of aging on the microstructure and mechanical properties of AZ80 and ZK60 wrought magnesium alloys was studied with optical microscope and mechanical testers. The results demonstrate that both the tensile strength and elongation of AZ80 alloy increase firstly and then decrease as the aging temperature rises, the peak values appear when the aging temperature is 170 ℃ The hardness of ZK60 alloy increases firstly and then decreases as the aging temperature rises, and the hardness reaches its peak value at 170 ℃. However, the toughness of the alloy is just the opposite. Moreover, ZK60 alloy has good performances in both impact toughness and other mechanical properties at the aging temperature from 140 ℃ to 200 ℃.

Effect of VC/Cr_3C_2 on microstructure and mechanical properties of Ti(C,N)-based cermets

Effects of VC/Cr3C2 on the microstructure and mechanical properties of Ti（C,N）-based cermets were studied. The microstructure was investigated by means of optical microscopy, X-ray diffractometry as well as scanning electron microscopy in combination with energy dispersive spectrometry. Mechanical properties, such as transverse rupture strength, hardness and fracture toughness, were measured. The results show that there are black core-grey rim structure and white core-grey rim structure in the microstructure. The grains become fine due to the VC/Cr3C2, and the grains of cermet added with 0.75VC/0.25Cr3C2 are refined most remarkably. The black core becomes finer with the increase of VC addition and rim phase becomes thicker with the decrease of Cr3C2 addition. The porosity increases with the increase of VC addition in VC/Cr3C2. Compared with the cermet free of VC/Cr3C2, the transverse rupture strength and hardness of cermets with VC/Cr3C2 are both improved, and the maximum values are both found for the cermet with 0.25VC/0.75Cr3C2. The fracture toughness can be effectively promoted by adding VC/Cr3C2 with an appropriate ratio of VC to Cr3C2, and the maximum value is found for the cermet with 0.5VC/0.5Cr3C2.

Effect of heat treatment on microstructures and mechanical properties of sand-cast Mg-10Gd-3Y-0.5Zr magnesium alloy

The microstructure, mechanical properties and fracture behavior of sand-cast Mg-10Gd-3Y-0.5Zr alloy （mass fraction,%） under T6 condition （air cooling after solid solution and then aging heat treatment） were investigated. The optimum T6 heat treatments for sand-cast Mg-10Gd-3Y-0.5Zr alloy are （525 ℃, 12 h＋225 ℃, 14 h） and （525 ℃, 12 h＋250 ℃, 12 h） according to age hardening curve and mechanical properties, respectively. The ultimate tensile strength, yield strength and elongation of the Mg-10Gd-3Y-0.5Zr alloy treated by the two optimum T6 processes are 339.9 MPa, 251.6 MPa, 1.5%and 359.6 MPa, 247.3 MPa, 2.7%, respectively. The tensile fracture mode of peak-aged Mg-10Gd-3Y-0.5Zr alloy is transgranular quasi-cleavage fracture.

Microstructure evolution and mechanical properties of extruded Mg-12Zn-1.5Er alloy

The microstructure and mechanical properties of the cast and extruded Mg-12Zn-1.5Er alloys were investigated. The I-phase observed in the cast Mg-12Zn-1.5Er alloy was broken during hot extrusion. The microstructure of the alloy was refined due to the dynamic recrystallization, and the equiaxed grains have size in the range of 2 5 μm. Moreover, a great deal of nano-scale particles precipitate in the recrystallized grains. Compared with the cast one, the extruded alloy shows a great improvement on the mechanical properties as the result of refined microstructure, the dispersed I-phase and the fine precipitates. The ultimate tensile strength and the yield tensile strength of this extruded alloy are 359 and 318 MPa, respectively.

Microstructure,mechanical properties and creep resistance of Mg-(8%-12%)Zn-(2%-6%) Al alloys

The microstructural characteristics, mechanical properties and creep resistance of Mg-（8%-12%） Zn-（2%-6%） A1 alloys were investigated to get a better overall understanding of these series alloys. The results indicate that the microstructure of the alloys ZA82, ZA102 and ZA122 with the mass ratio of Zn to A1 of 4-6 is mainly composed of a-Mg matrix and two different morphologies of precipitates （block τ-Mg32（Al, Zn）49 and dense lamellar ε-Mg51Zn20）, the alloys ZA84, ZA104 and ZA124 with the mass ratio of 2-3 contain α-Mg matrix and only block r phases, and the alloys ZA86, ZA106 and ZA126 with the mass ratio of 1-2 consist of a-Mg matrix, block r precipitates, lamellar Ф-Al2Mg5Zn2 eutectics and flocculent β-Mg17Al12 compounds. The alloys studied with the mass ratio of Zn to A1 of 2-3 exhibit high creep resistance, and the alloy ZA124 with the continuous network of r precipitating along grain boundaries shows the highest creep resistance.

Influence of forging process on microstructure and mechanical properties of large section Ti-6.5Al-1Mo-1V-2Zr alloy bars

The mechanical properties, microstructure and tensile fracture of Ti-6.5AI-IMo-IV-2Zr large section bars produced by three diffrent forging processes were investigated. The results show that when billet forging and finish forging were conducted by means of fullering at high and low temperature of r-region, respectively; the microstructure of forged bar is coarse Widmanstaten structure; the mechanical properties, especially the reduction of cross-sectional area, are poor, and the room temperature tensile fracture presents a brittle feature. While billet forging was carried out by upset-fullering at high temperature of the r-region, and finish forging was proceeded through fullering at （a＋fl）-region, the microstructure of forged bar was a duplex structure, the bar has better comprehensive mechanical properties, and the room temperature tensile fracture reveals a ductile feature. In order to obtain qualified Ti-6.SAI-IMo-IV-2Zr alloy bar, it is the key that as-cast microstructure should be completely broken during billet forging, and the forging temperature and deformation are also well controlled upon finishing forging.

Microstructure and room temperature mechanical properties of NiAl-Cr(Mo)-(Hf,Dy) hypoeutectic alloy prepared by injection casting

The NiA1 Cr（Mo） （Hf, Dy） hypoeutectic alloys were prepared by conventional casting and injection casting techniques respectively, and their microstructure and room temperature mechanical properties were investigated. The results reveal that with the addition of Hf and Dy, the Ni2AIHf Heusler phase and NisDy phase form along the NiAI/Cr（Mo） phase boundaries in intercellular region. By the injection casting method, some Ni2AIHf Heusler phase and NisDy phase transform into Hf and Dy solid solutions, respectively. Moreover, the microstructure of the alloy gets good optimization, which can be characterized by the fine interlamellar spacing, high proportion of eutectic cell area and homogeneously distributed fine Ni2AIHf, NisDy, Hf solid solution and Dy solid solutions. Compared with conventional-cast alloy, the room temperature mechanical properties of injection-cast alloy are improved obviously.

Microstructures and properties of A356-10%SiC particle composite castings at different solidification pressures

A356-based metal matrix composites with 10% SiC particles of 10 rtm were fabricated by stir casting and direct squeeze casting process under applied pressures of 0.1 （gravity）, 25, 50 and 75 MPa. The microstructures and mechanical properties of the as-cast and T6 heat-treated castings were investigated. The results show that as the applied pressures increase, the casting defects as particle-porosity clusters reduce and the incorporation between the particles and matrix can be improved. The tensile strength, hardness, and coefficients of thermal expansion （CTE） increase with the increase of the pressures. Compared with the as-cast composite castings, the tensile strength and hardness of the heat-treated casting are improved whereas CTEs tend to decrease in T6-treated condition. For the gravity cast composites, there are some particle-porosity clusters on the fracture surface, and the clusters are hardly detected on the fracture surface of the samples solidified at the external pressures. Different fracture behaviors are found between the composites solidified at the gravity and imposed pressures.

Shear deformation and plate shape control of hot-rolled aluminium alloy thick plate prepared by asymmetric rolling process

Asymmetric rolling （ASR）, as one of severe plastic deformation （SPD） methods to make ultra-fine materials with enhanced performance is mainly used to prepare foil and thin strip. The asymmetrical rolling was achieved by adjusting the diameters of the upper roll and the bottom roll and was used to prepare hot-rolled thick plate of 5182 aluminium alloy. The shear deformation and plate shape control were experimentally studied. The experimental results show that asymmetrical rolling has a significant effect on metal deformation stream and can somehow refine microstructure and improve the uniformity of microstructure and properties. The asymmetrical rolling process can also reduce the rolling force. However, bending of rolling plate often happens during asymmetrical rolling process. The factors affecting the bending were discussed.