Microstructure and mechanical properties of E36 steel joint welded by underwater wet welding

The microstructure and mechanical properties of E36 steel joint welded by underwater welding using flux-cored wire are comprehensively investigated. The welding depth, welding current and welding voltage is 4 m, 130 A and 32 V, respectively. The weld metal is ferrite which varies in size, with carbide particles distributed on it, while the microstructure of HAZ is mixture of martensite of different size and some tempered structure. The microhardness of the weld metal is 190 HV. Almost all the tensile specimens fracture in weld metal and the average tensile strength of joint is 390 MPa, which is equal to 80% that of base metal. The tensile fracture morphology of joint presents obviously the characterization of brittle fracture, which displays the features of cleavage fracture and intergranular fracture.

ZVS of arc welding inverter in light load

It is very difficult for arc welding inverter to realize Zero-Voltage-Switching （ZVS） because the load of arc welding inverter changes violently. An improved PS-FB-ZVS-PWM （ Phase-Shifted Full-Bridge Zero-Voltage-Switching Pulse-Width-Modulation） topology is proposed in this paper. A saturate resonant inductor is in series with the primary side of the transformer, while an auxiliary inductor is in parallel with the secondary side of the transformer to increase reactive current in light load or unload state, so the zero voltage switching of power devices is realized during switching course in light load or unload state.

Influence of arc pressure on the forming of molten pool in tungsten inert gas arc butt welding with micro gap for tantalum sheet

Arc pressure is the key influencing factor to forming of molten pool. Countering the characteristic of tungsten inert gas arc welding with micro gap for tantalum sheet, according to the fundament of arc physics, a distribution model of arc pressure and forming mechanism of molten pool with micro butt gap are proposed, and the influences of arc pressure on forming of molten pool are discussed. Experimental researches for the dynamic formation process of weld molten pool by using high-speed vidicon camera show that when butt gap is appropriate, that is from 0. 1 to 0. 15 mm, molten metals formed on two workpiece uplift and grow up first, then are fused and form uniform molten pool finally.

Refill friction stir spot welding (RFSSW): a review of processing, similar/dissimilar materials joining, mechanical properties and fracture mechanism

Refill friction stir spot welding(RFSSW)provides a novel method to join similar and/or dissimilar metallic materials without a key-hole in the center of the joint.Having the key-hole free characterization,the similar/dissimilar RFSSW joint exhibits remarkable and endurable characteristics,including high shear strength,long fatigue life,and strong corrosion resistance.In the meanwhile,as the key-hole free joint has different microstructures compared with conventional friction stir spot welding,thus the RFSSW joint shall possess different shear and fatigue fracture mechanisms,which needs further investigation.To explore the underlying failure mechanism,the similar/dissimilar metallic material joining parameters and pre-treatment,mechanical properties,as well as fracture mechanisms under this novel technology will be discussed.In details,the welding tool design,welding parameters setting,and the influence of processing on the lap shear and fatigue properties,as well as the corrosion resistance will be mainly discussed.Moreover,the roadmap of RFFSW is also discussed.

Characterization of ceramic coating on ZK60 magnesium alloy prepared in a dual electrolyte system by micro-arc oxidation

Micro-arc oxidation （MAO） process was cartied out in an optimized dual electrolyte system to fabricate a compact, smooth, and corrosion resistant coating on ZK60 Mg alloy. The microstructural characteristics of coating were investigated by scanning electron microscopy （SEM） coupled with an energy dispersive spectrometer （EDS） and X-ray diffraction （XRD）. Test of mass loss was conducted at a 3.5 % NaCl solution to assess the resistance to corrosion. The bonding strength between the coating and ZK60 substrate was evaluated using scratch experiment. The results reveal that MgA1204 and MgO are the main phases of ceramic coating obtained in the dual electrolyte system. The corrosion rate of coating prepared in the optimized dual electrolyte is only 0.0061 g.m-2.h-1, which demonstrates excellent corrosion resistance. This is mainly due to the compact, uniform coating with high bonding strength.

Effects of Ga and In on the properties of cadmium-free Ag-Cu-Zn filler metal

Melting temperature, spreadability, mechanical properties and the microstructures of joints brazed with silver-base filler metals including different amounts of Ga and/or In were studied respectively in this paper, and the results show that the melting temperature of the silver-base filler metals is decreased, spreadability of the silver-base filler metals is improved, and the microstructures of silver-base filh, r metals are refined obviously with the addition of Ga and/or In. Using copper and brass plates as base metal and brazing with flame method, the mechanical properties of the lap-joint and butt joint were also examined and analyzed respectively, and the results indicate that the fracture position of two kinds of brazed joints occurred on the base metal, except for the lap-joint of brass, which shows better mechanical properties of the joints brazed with the silver- based filler metals including Ga. For the lap-joint of brass, the tensile strength gradually increased with the increase of Ga content, while the addition of In has little effect on mechanical properties. It is also found that the best comprehensive properties of cadmium-free Ag-Cu-Zn filler metals are obtained when Ga content is about 3.0 wt. % and In content is between 1.5 wt. % and 2. 0 wt. %.

Microstructure evolution of HAZ in the multi-pass underwater wet welded joints

The microstructure evolution of heat-affected zone （HAZ） in the multi-pass underwater welded joints is investigated in the present work, and it can be characterized by four zones, marked as Region A, B, C and D, respectively. The microstructure in Region A is the mixture of lath martensite and residual austenite. Besides this structure, lots of acicular ferrite appears in Region B as well, and the grain size becomes larger. Lath ferrite combined with granular bainite is observed in Region C. In Region D, tempered sorbite, granular bainite and fine acicular ferrite are found within the grains, while massive ferrite and Widmanstatten structure are distributed along the grain boundary： The thermal effect of multi-pass welding makes the microstructure and property more and more uniform in the ttAZ, and the largest hardness 356 HV in the HAZ appears in Region A.

Effect of Ce on solderability of Sn-Cu-Ni solder

Abstract A small amount of rare earth Ce was added to Sn-Cu-Ni solder alloy, and the solderability of Sn-0. 5Cu-0. 05Ni- xCe solders on Cu and Au/Ni/Cu substrates was determined by the wetting balance method. The effects of atmosphere, temperature, substrate, and Ce addition on the solderability of Sn-Cu-Ni-xCe solder were studied, respectively, and Auger electron spectroscopy （ AES） analysis in the depth direction of the alloy was carried out to discuss the effect of Ce addition on the solderability. The results indicate that the greatest improvement on the solderability of Sn-Cu-Ni-xCe is obtai^d with around O. 05wt. % -0. 07wt. % Ce addition, for Ce element keeps high content in a specific area in the depth direction from the surface of Sn-Cu-Ni alloy, which decreases the surface tension of molten solder. It is also found that the solderability of Sn-Cu-Ni-xCe solder on Au/Ni/ Cu substrate is better than that on Cu substrate. In N2 atmosphere, the wetting times of Sn- Ca-Ni-xCe alloys are reduced by 10% - 35% , below 1 s at 260 ℃ on Ca substrate, and about 1s at 250 ℃ on Au/Ni/Ca substrate.

Cyclic deformation behaviors of Ti-46Al-2Cr-2Nb-0.15B alloy during thermo-mechanical fatigue tests

Thermo-mechanical fatigue tests were carried out on the gamma-TiAl alloy in the temperature range of 500-800℃ under mechanical strain control m order to evaluate its cyclic deformation behaviors at elevated temperature. Cyclic deformation curves, stress-strain hysteresis loops under different temperature--strain cycles were analyzed and dislocation configurations were also observed by TEM. The mechanisms of cyclic hardening or softening during thermo-mechanical fatigue （TMF） tests were also discussed. Results showed that thermo-mechanical fatigue lives largely depended on the applied mechanical strain amplitudes, applied types of strain and temperature. On the hysteresis loops appeared two apparent asymmetries： one was zero asymmetry and the other was tensile and compressive asymmetry. Dislocations configuration and slip behaviors were contributed to cyclic hardening or cyclic softening.

The Corrosion Behavior of Ni-Y Binary Alloys in Air and in Molten (0.62Li,0.38K)_2CO_3 Mixture at 650℃

The corrosion behavior of pure Ni and of binary Ni-Y alloys containing 1wt%,3wt%,5wt% Y,respectively,was investigated in air and in the eutectic (0.62Li,0.38K)2CO3 mixture at 650 ℃.The alloys are two-phase composed of γ-Ni solid solution and intermetallic compound Ni17Y2.The experimental results indicated that the corrosion of Ni-Y alloys in air and in molten salts,respectively,produced an external NiO scale with a small amount of Y2O3 and an internal oxidation region composed of Ni and Y2O3 resulting from the oxidation of the intermetallic phase Ni17Y2.The presence of yttrium in the alloy had a positive effect on the lithiation reaction of NiO during immersion in the melt.

Effect of interlayer on the mechanical properties of YG8 hard carbide/40Cr steel brazed joints

The effects of Cu foil and Ni foil on the mechanical properties of YG8 hard carbide/4OCr steel brazed joints were investigated. The results show that both Cu foil and Ni foil were beneficial to decrease the residual stress and enhance the joint strength. Moreover, Ni foil exhibited the better impact on enhancing the joint strength relative to Cu foil. When Cu foil was used as interlayer material, the key factor to restrain the joint strength was the massive and quick dissolution of Cu. Therefore, in order to prevent the excessive dissolution of Cu foil, the process parameter should be controlled strictly in the brazing process.

Strength and interfacial microstructure of Si3N4 joint brazed with amorphous Ti-Zr-Ni-Cu filler metal

In this paper, the vacuum brazing of Si3N4 ceramic was carried out with Ti40Zr25Ni15Cu20 amorphous filler metal. The interfacial microstructure was investigated by scanning electron microscopy （ SEM ）, energy dispersive spectroscopy （EDS） etc. According to the analysis, the interface reaction layer was mode up of TiN abut on the ceramic and the Ti-Si, Zr-Si compounds. The influence of brazing temperature and holding time on the joint strength was also studied. The results shows that the joint strength first increased and then decreased with the increasing of holding time and brazing temperature. The joint strength was significantly affected by the thickness of the reaction layer. Under the same experimental conditions, the joint brazed with amorphous filler metal exhibits much higher strength compared with the one brazed with crystalline filler metal with the same composition. To achieve higher joint strength at relatively low temperature, it is favorable to use the amorphous filler metal than the crystalline filler metal.

Interfacial structure and joint strengthening in arc brazed galvanized steels with copper based filler

Galvanized steel sheets were joined by tungsten inert gas(TIG) and metal inert gas(MIG) brazing process using copper based filler. The results show that the joint zone hardness is higher than that of the base material or copper filler from the microhardness tests of TIG brazing specimens, and the fracture spot is at the base materials zone from the tensile tests of MIG brazing specimens. Examination using energy dispersive X-ray analysis reveals the presence of intermetallic compound Fe5Si3(Cu) in the joint. The dispersal of fine Fe5Si3(Cu) particles is the main strengthening factor for the joint. The Fe5Si3(Cu) particles are determined to arise from three sources, namely, spot micro-melt, whisker-like fragmentation and dissolve-separation actions.

FEM simulation on residual stress distribution during diffusion bonding between Ti （ C, N） metallic ceramic/interlayer/40Cr steel

Based on ANSYS FEM software, the distribution of residual stress in the diffusion bonding joints between Ti（ C,N） metallic ceramic/interlayer/4OCr steel was calculated and experimentally ver^ed. The results showed that the trend on the distribution of residual stress field in the joints was not changed with the use of interlayer. The maximum residual stress was always located in metallic ceramic with area ranging from 1 mm to 4 mm to the interlayer. The maximum residual stress in the joints was also affected by diffusion temperature. The satellite pulse current during the initial stage on diffusion bonding can promote the formation of liquid film at the interface, by which diffusion temperature and loading pressure can be greatly decreased. The crack initiation was easily produced at the corner of Ti （ C, N） metallic ceramic close to the interlayer. If a higher residual stress produced in the joints, the crack was propagated into the whole ceramic.

Effect of combinative addition of mischmetal and titanium on the microstructure and mechanical properties of hypoeutectic Al-Si alloys used for brazing and/or welding consumables

Effects of mischmetal（RE） and/or Ti modifier on the microstructure including α-Al dendrites, eutectic Si phases and other secondary phases of Al-Si brazing and/or welding alloys were investigated by differential scanning calorimetry（DSC）, optical microscopy（OM）, scanning electron microscopy（SEM）. The DSC results showed that an addition of RE decreased the eutectic temperature and caused supercooling, promoting the nucleation of eutectic Si crystals. In addition, the maximum temperature of the first endothermic peak varied with the different RE contents, which had a good correlation with the microstructural modification of the eutectic Si phase. The α-Al dendrites were well refined by increasing the cooling rate or adding 0.08 wt.% of Ti. When 0.05 wt.% RE was added to the Al-5Si-0.08 Ti alloy, the morphology of eutectic Si phase was transformed from coarse platelet to fine fibers and the mechanical properties of the resulting welding rod were well improved. Whereas, when excess RE was added, a large number of β-Fe phases appeared and the aspect ratios of β-Fe phases increased. The morphologies and chemical components of two kinds of RE-containing intermetallic compounds（IMCs） were also discussed.

Ti/Fe EUTECTIC REACTION PROCESS

To obtain satisfactory joining between titanium alloys end stainless steel, it is of great significance to study the process of Ti-Fe eutectic reaction. The preliminary studies about the liquid forming, spreading end the structure of the contact reaction between pure Ti and pure Fe are carried out at 1 120℃ for different holding times in high-frequency induction heated vacuum furnace. The results show that for Fe（particle-like）/Ti（plate-like） contact reaction couples, owing to Fe＇s higher density then titanium＇s, the Fe/Ti eutectic reaction develops in the thickness direction of plate-like Ti, named ＂deposition effect＂. Then the eutectic reaction can be realized without the inter-diffusion between Ti end Fe atoms, so the formation rate of the liquid phase is very quick. For Ti （particle-like）/ Fe （plate-like） contact reaction couples, the eutectic reaction has a strong direction, i.e. the eutectic liquid is formed mostly at the Ti side, which leads to much dissolution of Ti particle end very little dissolution of the Fe base metal. It can be seen that the diffusion rate of Fe in Ti determines the whole process of the eutectic reaction, behaved as that the dissolution rate of Ti （particle-like）/ Fe （plate-like） is much lower then that of Fe（particle-like）/Ti（plate-like）, end the dissolution rate of Ti obeys the square root law. Whatever means the Ti, Fe are assembled by, only dissolution process can be founded, the spread phenomena is unobvious, which is concerned with the formation of the inter- metallic compounds end the ＂deposition effect＂ of Fe.

Microstructures and properties of SnZn-xEr lead-free solders

The Sn9Zn eutectic alloy is the nontoxic lead-free solders alternative having a melting temperature which is closest to that of the eutectic SnPb alloy. In order to improve the properties of SnZn lead-free solders, 0-0.5 wt.% of rare earth Er was added to the base alloys, and the microstructures were studied. Results showed that the addition of rare earth Er could enhance the wettability of SnZn solders, with 0.08%Er addition, the spreading area gavc an 19.1% increase. And based on the mechanical testing, it was found that the tensile force and shear force of SnZn-xEr solder joints could be improved significantly. Moreover, the oxidation resistance of SnZn0.08Er solder was better than that of SnZn solder, in addition, it was found that trace amounts of rare earth Er could refine the microstructures of SnZn solders, espe- cially for Zn-rich phases, and excessive amount of rare earth Er led to a coarse microstructure.

Improving friction stir weldability of Al/Mg alloys via ultrasonically diminishing pin adhesion

Formation of intermetallic compounds （IMCs） during friction stir welding （FSW） of alu- minum/magnesium （AI/Mg） alloys easily results in the pin adhesion and then deteriorates joint formation. The severe pin adhesion transformed the tapered-and-screwed pin into a tapered pin at a low welding speed of 30 mm/min. The pin adhesion problem was solved with the help of ultrasonic. The weldability of Al/Mg alloys was significantly improved due to the good material flow induced by mechanical vibration and the fragments of the IMCs on the surface of a rotating pin caused by acoustic streaming, respectively. A sound joint with ultrasonic contained long Al/Mg interface joining length and complex mixture of AI/Mg alloys in the stir zone, thereby achieving perfect metallurgical bonding and mechanical interlocking. The ultrasonic could broaden process window and then improve tensile properties. The tensile strength of the Al/Mg joint with ultrasonic reached 115 MPa.

Effect of LaCrO_3 coating on high temperature oxidation of type 316 stainless steel

A dense and conductive LaCrO3 coating was prepared on type 316 stainless steel （316 SS）, aiming at exploring its potential appli-cations in SOFC and in other high temperature environments. Powder of LaCrO3 with perovskite structure was synthesized by sol-gel method. LaCrO3 coating on 316 SS substrate was obtained by slurry coating technique. The microstructure of the coating on 316 SS after sintering in air at 800 and 900 ℃ for 200 h was characterized. The effect of LaCrO3 coating on oxidation resistance of the steel in air was also investi-gated. The results showed that the coating was adhesive to the substrate and improved greatly the oxidation resistance of the alloy.

Microstructure,phase composition and wear resistance of low valence electron concentration Al_(x)CoCrFeNiSi high-entropy alloys prepared by vacuum arc melting

The low valence electron concentration(VEC)Al_(x)CoCrFeNiSi(x=0.5,1.0,1.5 and 2.0)high-entropy alloys(HEAs)were designed by the fundamental properties of the constituent elements and prepared by vacuum arc melting method.The effects of Al addition on the crystal structure and microstructure were investigated.The microhardness and wear property were also researched.The results showed that the microstructure transformed from dendritic crystal to equiaxed crystal.It was found that FCC phase gradually decreased with the increasing Al content and disappeared until in a composition of 1.0 in Al_(x)CoCrFeNiSi HEAs.Little FCC phase was found with continuously adding Al,while the phase fraction of BCC increased from 85.0% to 91.8%,and VEC decreased from 7.00 to 6.14.The microhardness was increased gradually from 598 up to 909 HV with addition of Al from 0.5 to 2.0.It was the same of the compressive strength results,which improved from 1200 to 1920 MPa.The wear coefficient and mass loss were in line with mechanical properties evolution,which was attributed to the microstructure transformation into equiaxed crystal and the increase in BCC phase.