Rare Metals2020年第3期

Microstructure and properties of continuous casting Ag-28Cu-8Sn alloy fabricated by dieless drawing

Ji-Heng Fang Ming Xie Ji-Ming Zhang You-Cai Yang Yong-Tai Chen Song Wang Man-Men Liu Jie-Qiong Hu

State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metal

作者简介：*Ming Xie,e-mail:powder@ipm.com.cn;

收稿日期：18 October 2017

基金：financially supported by the National Natural Science Foundation of China (Nos.U1602271 and U1302272);

Microstructure and properties of continuous casting Ag-28Cu-8Sn alloy fabricated by dieless drawing

Ji-Heng Fang Ming Xie Ji-Ming Zhang You-Cai Yang Yong-Tai Chen Song Wang Man-Men Liu Jie-Qiong Hu

State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metal

Abstract：

Ag-28Cu-8Sn(wt%) alloy is a widely used brittle silver-based brazing filler metal.The wire of brazing filler metal was prepared by continuous casting process and dieless drawing technology.The phase structure was measured by X-ray diffraction(XRD),and the microstructure of wetting interface,cast states,processing states and fracture morphologies were characterized by the optical microscopy(OM) and scanning electron microscopy(SEM),respectively.The electrical conductivity,hardness,tensile strength and elongation rate were tested as well.Furthermore,the solid-liquid phase temperature was measured by a differential scanning calorimeter(DSC),and the wettability of brazing filler metal was tested by spreading method.The outcomes obtained show that the as-cast microstructure is a typical three-zone structure,including region of surface fine grain,zone of columnar grain and region of center equiaxed crystal.Ag-28Cu-8Sn alloy is mainly composed of Ag-rich a-phase,Cu-rich pphase and intermediate compounds.Grain refinement appears in the cross section,as for grains of the longitudinal section,the shape is changed from ribbon to fiber to form a silk texture.The strength and hardness improve with the increase in the true strain,while the conductivity and elongation are reduced.Furthermore,the solid-phase temperature is 605.9℃,and the liquid-phase temperature is 725.1℃.The spreading area of Ag-28Cu-8Sn brazing filler metal is 174 mm²,and the metallurgical bonding occurs between Ag-28Cu-8Sn brazing filler metal and Cu matrix.In addition,compared with cold drawing process,there are not any microcracks at the fracture morphology for the alloy fabricated by dieless drawing.The dieless drawing process overcomes some processing defects of traditional cold drawing,and the processing performance of Ag-28Cu-8Sn alloy is improved.

Keyword：

Continuous casting; Cold drawing; Dieless drawing; Microstructure; Properties;

Received： 18 October 2017

1 Introduction

With the advantages of low vapor pressure,moderate melting point,high strength of solder joints and excellent wettability on copper,nickel,steel and Kovar alloy [ 1, 2] ,Ag-28Cu-8Sn alloy becomes a new kind of brazing filler metal and plays a significant role in the aviation,aerospace,electronics,electrical and other fields [ 3, 4] .However,when Sn,In,Ge,Si and other low-melting-point components are added to the alloy system,a brittle intermediate compound is easily formed in these components in the alloy structure,which led to the deterioration of processing performance,and it is difficult to prepare the ideal alloy wire using rolling,cold drawing and other traditional pressure processing methods [ 5, 6] .The addition of Sn to the Ag-28Cu alloy reduces the melting point of brazing filler metal,but it also generates brittle intermediate compounds and deteriorates processing performance [ 7, 8, 9] .Ag-28Cu-8Sn is proved to be a typical brittle mid-temperature brazing filler metal with poor processing performance.Compared with the conventional cold drawing process,dieless drawing technology,a heat working method,realizes plastic forming by controlling heating temperature without drawing dies.There are several significant advantages of dieless drawing [ 10, 11, 12] ,such as no friction,smaller drawing force,larger cross section shrinkage,larger one-pass area reduction,easy to achieve automatic control.Therefore,the dieless drawing technology is applied to the preparation of Ag-28Cu-8Sn alloy in order to explore a more convenient and efficient processing technology to overcome the defects of traditional cold drawing processing.It is also helpful to solve the problem of poor processing performance of other brittle brazing filler metal.

Thus far,the domestic and foreign scholars have conducted numerous theoretical and experimental researches in the field of dieless drawing technology.Twohig et al. [ 13] observed the influence of key process parameters such as temperature,cooling rate and drawing speed on the drawing process of Ni-Ti alloy rods (5 mm).Furushima et al. [ 14] have been focused on the use of superplastic dieless drawing techniques for the fabrication of zirconia ceramic tubes.Chen et al. [ 15] and Liu et al. [ 16] simulated the temperature field of stainless steel bars fabricated by dieless drawing through the finite element method,and the temperature distribution of stainless steel bars was obtained.However,the effect of dieless drawing process on microstructure and properties of brittle alloys has not been explored,and the research on the application of the dieless drawing process in the precious metal alloy is rarely reported.Therefore,the purpose of this study is to reveal the effect of dieless drawing process on microstructure and properties of brittle Ag-28Cu-8Sn alloy.At the same time,the dieless drawing process can be extended to more brittle precious metal alloys.

In addition,compared with the ordinary casting techniques,the continuous casting technology remarkably enhances the quality of casting,increases yield of metal and achieves mechanical automation easily [ 17, 18, 19] .Therefore,Ag-28Cu-8Sn alloy bars are obtained by continuous casting technology.

2 Experimental

2.1 Processing of dieless drawing

Ag-28Cu-8Sn alloy bars (8 mm in diameter),obtained through continuous casting technology,were processed by vacuum annealing (400℃×1 h).Subsequently,the alloy bars were drawn to the target diameter (2 mm) on the intelligent dieless drawing equipment of the University of Science and Technology Beijing [ 20] ,and its working principle is depicted in Fig.1.And the optimal process parameters are as follows:deformation temperature of450℃,feeding speed of 0.5 mm·s^-1,drawing speed of0.8 mm·s^-1 and distance between cooler and heater of15 mm.The whole drawing procedure demanded 31 passes(cold drawing usually takes 85 passes,as a control group,the same alloy bars and annealing process were used in cold drawing,and the drawing speed was 0.3 mm·s^-1).In addition,the analytical samples were intercepted in the transverse and longitudinal direction of each dimension(Φ8 mm,Φ6 mm,Φ4 mm,Φ3 mm,andΦ2 mm).According to the true strain formula [ 21] η=ln(A₀/A₁),whereηis conductivity (%IACS),and A₀,A₁ are crosssectional area before and after deformation,respectively,the section size just corresponds to the true strain ofη=0,0.575,1.380,1.960,2.770.

Fig.1 Schematic diagram of continuous dieless drawing process [20]

2.2 Observation and testing of phase,microstructure and mechanical properties

The phase was investigated by means of D/max-RC X-ray diffractometer (XRD).Subsequently,the analytical samples were etched by corrosion solution (10 ml hydrogen peroxide,20 ml ammonia and 30 ml water),and the micro structure of wetting interface,casting states,working states and fracture morphologies were characterized by MM-4XC optical microscope (OM) and HITACHI S-3400N scanning electron microscope (SEM),respectively.Hardness was measured on the HV-5 Vickers hardness tester;tensile strength and elongation rate were measured on the AG-X100KN universal electronic testing machine.Eventually,the resistance was measured by the ZY9987 digital micro-ohmmeter,and it was converted to the electrical conductivity with formulaη=17.24L/(S×R) [ 22] ,where L is the effective length (mm),R is the resistance value (μΩ),and S is the average cross-sectional area (mm²).

2.3 Testing of brazing properties

The solidus-liquidus temperature was measured using NETZSCH STA409 PG/PC differential scanning calorimetry (DSC).According to the national standard GB11364-2008,wettability of brazing filler metal was tested by spreading method,which was tested in a vacuum tube furnace,and the experimental parameter are as follows:Cu as matrix (40 mm×40 mm×1 mm),brazing temperature of 640℃,0.2 g Ag-28Cu-8Sn brazing filler metal and holding time of 5 min;besides,the spread samples were scanned by scanner,and the spreading area of brazing filler metals was measured by graphic software.

3 Results and discussion

3.1 As-cast microstructure and phase of continuous casting Ag-28Cu-8Sn alloy

3.1.1 As-cast microstructure of continuous casting Ag-28Cu-8Sn alloy

The as-cast microstructure of Ag-28Cu-8Sn alloy is illustrated in Fig.2,showing that the microstructure of casting states is typical three-zone structure,including region of surface fine grain,zone of columnar grain and region of center equiaxed crystal [ 23, 24, 25] .Their characteristics are as follows.(1) Region of surface fine grain which possesses the average area width of 30μm is located in the chill crystal zone of castings.And uniformly distributed non-oriented fine equiaxed crystals are formed in this section.(2) As for the fine equiaxed crystal zone of ingot surface,grains grow preferentially when growth direction is parallel to the heat-extracted direction,but the growth of grains is inhibited when growth direction is not parallel to the heat-extracted direction.Owing to the difference in the growth rate of different directions,the number and shape of grains undergo changes in different directions.Eventually,the grains contact with each other to form columnar zone along the direction of heat dissipation.(3) The center of ingot is also composed of equiaxed crystals without orientation,although they are larger than the fine equiaxed grains in chill crystal zone.The nucleation of the grains begins at the geometric center of the grains,and the grains grow in a pergent manner,eventually forming a central equiaxed crystal.They are round or elliptical in shape,and the grain boundaries are intertwined with each other.

Fig.2 As-cast microstructure of continuous casting Ag-28Cu-8Sn alloy:a simulation result of ProCAST software and b metallographic image

3.1.2 Phase of continuous casting Ag-28Cu-8Sn alloy

According to the phase diagram of Ag-Cu-Sn [ 26] ,there are solid solution phase (α-phase) with Ag as solvent and solid solution phase (β-phase) with Cu as solvent.Additionally,Sn exists in solid Ag and solid Cu,and Sn found in Ag and Cu is mainly in the form of intermediate compounds.The Ag-28Cu-8Sn alloy was analyzed by energydispersive spectroscopy (EDS);the results are shown in Fig.3 and Table 1.The above results show that the white segregation phase is Ag solid solution phase,the black segregation phase is Cu solid solution phase and Sn is distributed in them.That is to say,Sn exists in solid-state Ag and solid-state Cu.The presence of phase in Ag-28Cu-8Sn alloy can be further analyzed by XRD pattern.

XRD pattern of Ag-28Cu-8Sn alloy is illustrated in Fig.4.Ag-28Cu-8Sn alloy is mainly composed of Ag-richα-phase (fcc structure) and Cu-richβ-phase (complex structure).In addition,there are also Ag_6.7Sn,Cu_0.85Sn_0.15,Cu₃Sn and other intermediate compounds.Among them,α-phase is plastic phase,butβ-phase and intermediate compounds are brittle phases.Sn content has a direct impact on the quantity ofβ-phase and intermediate compounds,and the higher the Sn content is,the more the brittle phases are,which leads to the deterioration of processing performance [ 27] .There are some defects in the cold drawing process of Ag-28Cu-8Sn alloy,such as serious work hardening,low drawing deformation rate,short service life of the mold,high frequency of broken wire,large energy consumption [ 28, 29, 30] .It is,therefore,an urgent task to find a kind of advanced preparation technology to overcome the defects of cold drawing.

Fig.3 BSE image of Ag-28Cu-8Sn alloy by continuous casting

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Table 1 EDS analysis results for component of marking points on microstructure of Ag-28Cu-8Sn alloy in Fig.3

Fig.4 XRD pattern of continuous casting Ag-28Cu-8Sn alloy

3.2 Effects of deformation on microstructure of continuous casting Ag-28Cu-8Sn alloy

Figure 5 shows the microstructures of Ag-28Cu-8Sn alloy under different deformations.Ag-28Cu-8Sn alloy presents clear morphology and homogeneous compositions,the white phase is Ag-richα-phase,and the black phase is Curichβ-phase.The phase size decreases gradually with true strain increasing on the cross section,which is attributed to the local slip and stress cracking of grain [ 31] .In addition,for the micros truc ture of the cross section,compared with the previous research on the preparation of Ag-28Cu-8Sn by cold drawing,the average phase size of dieless drawing is larger than that of cold drawing under the same true strain.This is due to the fact that,with the development of dieless drawing process,the diameter of the wire decreases with the increase in the applied tension,and the phase on the microstructure of the wire becomes thinner and longer.But dieless drawing belongs to hot working,and the heat treatment and deformation are going on simultaneously.After the moment of grains become elongated,the activation energy effect of high temperature and the enhanced grain boundary diffusion can cause the black and white phases to swallow up each other.Eventually,the average size of the phase becomes larger.For the longitudinal section,when the true strain is 0.575,the grains are elongated in the direction of stretch.White phase and black phase present a zonal distribution with irregular and undulating strip edge.With the increase in true strain,the banded structure gradually disappears into fibrous distribution which gives rise to the deformation texture.Fibrous structure is wide and uneven when the true strain is 1.96,but whenη=2.770,the fibrous tissue is more prolonged and consecutive.The two-phase distribution is more uniform as well,indicating that deformation can promote the composition homogenization and eventually may bring changes in the properties of alloy.

Fig.5 SEM images of a-d cross section and e-h longitudinal section of continuous casting Ag-28Cu-8Sn alloy:a,eη=0.575;b,fη=1.380;c,gη=1.960;d,hη=2.770

3.3 Effects of deformation on properties of Ag-28Cu-8Sn alloy

3.3.1 Effect of deformation on hardness of Ag-28Cu-8Sn alloy

Figure 6a shows the curve of hardness,as far as the change of hardness is concerned.On the one hand,with the increase in cold-drawn deformation,the dislocation density increases,the interaction between the dislocations increases,and a large number of entanglement and fixed dislocations are formed [ 32] .These changes aggravate the movement resistance of other residual dislocations.Eventually,the effect of work hardening comes into being.On the other hand,the grain size decreases gradually under the action of drawing force.Fine-grained metal has higher strength and hardness than coarse-grained metal at room temperature [ 33] ,that is,grain refinement strengthening.Ultimately,hardness increases under the combined action of work hardening and grain refinement strengthening.Compared to cold drawing,the dieless drawing belongs to the hot working.The softening effect caused by dynamic recovery and dynamic recrystallization partially counteracts the work hardening effect.In addition,recrystallization and grain growth during thermal processing lead to an increase in the average grain size and attenuate the grain refinement effect.Under the combined action of softening effect and grain refinement weakening,the hardness of dieless drawing decreases.

3.3.2 Effects of deformation on electrical conductivity of Ag-28Cu-8Sn alloy

Figure 6b shows the curve of electrical conductivity.The electrical conductivity gradually decreases with the increase in plastic deformation.In the first place,the lattice distortion,vacancy concentration and crystal defects increase as the deformation proceeds.These changes exacerbate the scattering of electromagnetic waves,which ultimately increases the resistivity [ 34] .Besides,the tensile stress increases the spacing of metal atoms and dynamic distortion of lattice,which also leads to larger resistivity.In addition,with the increase in the deformation,the phase structure becomes smaller,the boundary area becomes larger,and the scattering of electrons by the interface is large,which eventually leads to large resistivity.Ultimately,the electrical resistivities of the Ag-28Cu-8Sn alloy increase during the deformation process,resulting from the formation of intermediate metallic compounds(IMCs).IMCs have much higher electrical resistivity compared with Ag and Cu.The resistivity and conductivity are reciprocal,and electrical conductivity,therefore,decreases with the increase in true strain.Compared to cold drawing,the dynamic recovery of the dieless drawing process can reduce the crystal defects in the alloy,especially the concentration of vacancies and point defects,and improve the uniformity of the lattice electric field.As a result,the resistivity of the Ag-28Cu-8Sn alloy decreases.Finally,the electrical conductivity of the dieless drawing is improved.

Fig.6 Properties curves of continuous casting Ag-28Cu-8Sn alloy:a hardness-strain curve,b electrical conductivity-strain curve,c strength-strain curve and d elongation rate-strain curve

3.3.3 Effects of deformation on tensile strength of Ag-28Cu-8Sn alloy

Figure 6c shows the curve of tensile strength.The increase in tensile strength can be explained by the following reasons.(1) The smaller grain size corresponds to the larger total grain boundary area,which refers to more complicated grain boundaries and more severe blocking effect on the crack growth [ 35] .Eventually,the tensile strength has improved by the fine grain strengthening.(2) The grain shape changes from ribbon into a fibrous shape,which ultimately leads to the emergence of silk texture,and the tensile strength increases along the direction of deformation texture.(3) The work hardening effect also brings the increase in tensile strength.Compared to cold drawing,grain recovery,recrystallization and grain growth weaken the fine grain strengthening effect,and the softening effect partially offsets the work hardening caused by the deformation.Ultimately,the strength of the dieless drawing decreases.

3.3.4 Effects of deformation on elongation rate of Ag-28 Cu-8Sn alloy

Figure 6d shows the curve of elongation rate.In the first place,the effect of work hardening weakens the plasticity and toughness,and elongation rate,therefore,decreases as the deformation proceeds.Furthermore,the energy of plastic deformation is distributed to the smaller grains after grain refining,which results in more uniform plastic deformation and smaller stress concentration,and elongation rate increases at last [ 36] .The last but not the least,the elongation rate also increases with the effect of deformation texture.In the early stage of the drawing process,the effect of work hardening is dominant than the other considerations.Subsequently,the effects of grain refinement and deformation textures increase elongation rate with increasing true strain,which partially offsets the decrease in elongation rate caused by work hardening.Finally,after the stage of cold drawing,the decreased amplitude of elongation rate becomes small.Compared to cold drawing,although the weakening effect of grain refinement decreases the elongation,the softening effect of thermal processing partially counteracts the decrease in elongation caused by work hardening,and the softening effect plays a dominant role.Therefore,the ultimate performance of elongation increases.

3.4 Melting characteristics of Ag-28Cu-8Sn alloy

Figure 7 shows DSC curve of Ag-28Cu-8Sn brazing filler metal.The brazing filler metal has an endothermic peak at the position of 724.0℃.In addition to the main endothermic peak,there are several smaller endothermic peaks near the main endothermic peak.The presence of the smaller attached peaks indicates the generation of new phases,demonstrating the formation of intermediate compounds.The melting point of Ag-28Cu brazing filler metal is 780℃,and there is no temperature range for melting points [ 37] .But the solidus temperature of Ag-28Cu-8Sn is 605.9℃,liquidus temperature is 725.1℃,and melting temperature range is 119.2℃.These differences indicate that the addition of Sn significantly lowers the melting point but generates intermediate compounds accompanied with phase transition.This expands melting temperature range,and the greater the melting temperature range is,the worse the dispersion properties are,so the dispersion properties of Ag-28Cu-8Sn brazing filler metal are deteriorated.

3.5 Brazing properties of Ag-28Cu-8Sn alloy

The average spread area of the five tests was taken as the final result value,and the spreading area of Ag-28Cu-8Sn brazing filler metal is 174 mm².Under the same conditions,the spreading area of Ag-28Cu solder is 213 mm²,and the reason for the decrease in the spreading area of Ag-28Cu-8Sn brazing filler metal is as follows.(1) Ag6 7Sn,Cu_0.85Sn_0.15,Cu₃Sn and other intermediate compounds are formed in the brazing filler metal,which hinders the diffusion of filler metal and reduces the fluidity of liquid brazing filler metal [ 38] .(2) With the addition of Sn,the temperature range of the solid-liquid phase becomes large,and the spreading property of the brazing filler metal is poorer than that of the eutectic alloy or the brazing filler metal with small temperature range [ 39, 40, 41] .The microstructure of wetting interface formed by Ag-28Cu-8Sn brazing filler metal and Cu matrix is depicted in Fig.8.The wetting interface is pided into three zones:Cu matrix,diffusion zone (DZ) and residual brazing filler metal zone (WZ).The energy spectra of DZ are analyzed,and the results are given in Table 2.This area is mainly Cu-based solid solution phase,which is composed of Cu,Sn and a small amount of Ag.The content of Sn in the diffusion region is higher than that in Ag,showing that Sn is more inclined to react with Cu matrix material in brazing filler metal.According to Ref. [ 42] ,the dissolution enthalpy of Sn and Cu in the liquid brazing filler metal is-6 kJ·mol^-1,which is lower than those of Sn and Ag.As a result,Sn preferentially reacts with Cu substrate.In addition,the wetting interface indicates that the metallurgical reaction occurs between brazing filler metal and Cu matrix,eventually forming a metallurgical combination [ 43] .The metallurgical bonding contributes to the formation of welded joints with excellent quality.

Fig.7 DSC curve of Ag-28Cu-8Sn alloy

3.6 Fracture morphology of Ag-28Cu-8Sn alloy fabricated by cold drawing and dieless drawing process

Fracture morphology of Ag-28Cu-8Sn alloy fabricated by two processing methods is shown in Fig.9.First of all,for the fracture morphology of Ag-28Cu-8Sn alloy prepared by cold drawing,whenη=0.575,the alloy surface is very rough,dimple size is not uniform,and part of the equiaxed dimple size is large.The average diameter can reach16μm,and the three-dimensional tensile stress causes the shape of the partially equiaxed dimple to change from regular circle to oval or rectangle.In addition,several microcracks are scattered on the fracture of the alloy,the average length of the crack is about 10μm,and its position is close to the large equiaxed dimple.These cracks are initiated by the intermediate compounds of the Ag-28Cu-8Sn alloy;similar to the inclusions and the second phases,cracks appear first in these regions.Whenη=1.960,the microcracks still exist in the fracture.Compared with the true strain of 0.575,the shape of the large dimple is more regular,and the depth of the dimple is only half of the former,indicating that the plasticity of the alloy has declined.Whenη=2.770,the large dimple disappears,and the fracture is distributed with uniform equiaxed dimples.The smaller the dimple shape is,the shallower the depth is,and the lower the plasticity is [ 44] .The fracture mechanism under the above true strain is all the micropore aggregation fracture in the shear fracture,which belongs to the ductile fracture [ 45] .

Fig.8 SEM image of wetting interface of Ag-28Cu-8Sn alloy with Cu matrix

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Table 2 EDS analysis results for component of marking points on wetting interfaces in Fig.6b

In conclusion,as the deformation increases,the fracture morphology shows that the plasticity of the alloy decreases gradually.And the previous mechanical performance data also show that the alloy elongation decreases with the increase in the deformation.In addition,the alloy contains more micro-crack defects under cold drawing process,indicating the poor processing performance.

The fracture morphology of Ag-28Cu-8Sn alloy prepared by dieless drawing is similar to that of alloy prepared by cold drawing.But there are some differences:the microcracks are not found in the fracture surface;in addition,whenη=1.960 and 2.770,the average size of the dimples is larger than that of the alloy prepared by cold drawing.The above phenomenon can be attributed to the following reasons:dieless drawing is hot working with the increase of temperature;on the one hand,due to the increase in thermal motion,the diffusion ability of metal atoms in alloy is improved so that alloy elements near the second phase or intermediate compound are easy to expand,the stress distribution gradually becomes uniform,and microcracks are eventually reduced.On the other hand,the high-temperature activation can reduce the dislocation resistance and density of dislocation ring.The expansion rate of the small dimple is accelerated,and the small dimples connect to each other,which are easy to translate into larger dimples.Finally,the dimple size becomes larger,indicating that the deformation of materials becomes more complete,and plastic has improved.

Fig.9 SEM images of fracture morphologies of continuous casting Ag-28Cu-8Sn alloy under a-c cold drawing and d-f dieless drawing process:a,dη=0.575;b,eη=1.960;c,fη=2.770

In summary,the microcracks do not appear in the fracture morphology of the Ag-28Cu-8Sn alloy prepared by the dieless drawing,the size of the dimple increases,and the plasticity is enhanced.The results show that the dieless drawing technology improves the processability of the Ag-28Cu-8Sn alloy.

4 Conclusion

The as-cast micros truc ture of Ag-28Cu-8Sn alloy is a typical three-zone structure.Its phases contain Ag67Sn,Cu_0.85Sn_0.15,Cu₃Sn and some other intermediate compounds,and these brittle intermediate compounds deteriorate the processing performance.The processing performance of Ag-28Cu-8Sn alloy is improved by the dieless drawing process,and the defects of the traditional cold drawing are overcome,such as serious work hardening,low drawing deformation rate,short service life of the mold,high frequency of broken wire,large energy consumption and other issues.Compared with Ag-28Cu brazing filler metal,the addition of Sn reduces the temperature of the solid-liquid phase at 100℃;this meets the lower-temperature requirements of the brazing filler metal.But it expands the temperature range of the solid-liquid phase at 119.2℃,which reduces the spreading area of the brazing filler metal at 39 mm².The brazing filler metal and Cu matrix material can achieve better metallurgical bonding,which is conducive to the formation of a good welded joints.In addition,the strength and hardness improve with the increase in the true strain,while the conductivity and elongation are reduced.The processing micro structure and fracture morphology also change with the increase in deformation.The analysis of the microstructure and performance reveals the effect of dieless drawing process on the micros tructure and properties of brittle alloys,which fills the gaps in research at home and abroad in this area.Finally,in the follow-up work,the dieless drawing process can be applied to more brittle precious metal materials,to explore its feasibility to improve the processing performance of brittle brazing filler metal.

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