A new filler metal with low contents of Cu for high strength aluminum alloy brazed joints

The effect of Cu with low contents of 10, 12, 15 wt.% on the microstructure and melting point of Al–Si–Cu–Ni alloy has been investigated. Results showed that low-melting-point properties of Al–Si–Cu–Ni alloys with low contents of Cu were attributed to disappearance of Al–Si binary eutectic reaction and introduction of Al–Si–Cu–Ni quaternary reaction. With raising Cu content from 10 to 15 wt.%, the amount of complex eutectic phases formed during low temperature reactions (Al–Cu, Al–Si–Cu and Al–Si–Cu–Ni alloy reactions) increased and the melting temperature of Al–Si–Cu–Ni filler metals declined. Brazing of 6061 aluminum alloy with Al–10Si–15Cu–4Ni (all in wt.%) filler metal of a melting temperature range from 519.3 to 540.2 °C has been carried out successfully at 570 °C. Sound joints can be obtained with Al–10Si–15Cu–4Ni filler metal when brazed at 570 °C for holding time of 60 min or more, and achieved high shear strength up to 144.4 MPa.     

Effects of indium addition on properties and wettability of Sn–0.7Cu–0.2Ni lead-free solders

This paper reports the investigation on indium addition into Sn–0.7Cu–0.2Ni lead-free solder to improve its various performances. The effects of indium addition on melting temperature, coefficient of thermal expansion (CTE), wettability, corrosion resistance and hardness of the solder alloys were studied. The results showed that when the addition of indium was ⩽0.3 wt.%, the change in melting temperature of Sn–0.7Cu–0.2Ni–xIn solders was negligible, but the melting range of the solder alloy increased. The CTE and spreading area of Sn–0.7Cu–0.2Ni–xIn solders on copper both increased with the addition of indium. An optimal CTE was 17.5 × 10⁻⁶/°C by adding 0.3 wt.% indium. At this concentration, the spreading area of solder on copper was about 15.6% larger than that of Sn–0.7Cu–0.2Ni indium-free solder. The corrosion resistance also increased with the addition of indium increasing, and the corrosion rate of Sn–0.7Cu–0.2Ni–0.3In solder was reduced by 32.8% compared with Sn–0.7Cu–0.2Ni alloy after 14 days in 5% hydrochloric acid solution at room temperature. However, a decrease of 11.7% in hardness of the solder was found when 0.3 wt.% indium was added.     

Effect of weld peak temperature on the microstructure,hardness, and transformation kinetics of simulated heat affected zone of hot rolled ultra-low carbon high strength Ti–Mo ferritic steel

We describe here the microstructural evolution, precipitation behavior, and microhardness in simulated heat affected zone (HAZ) of Ti–Mo ferritic steel with the objective of elucidating the effect of weld peak temperature (PT) and defining the transformation kinetics. The study indicated that the microstructure of the hot rolled steel comprised of polygonal ferrite with average effective grain diameter of 5.5 μm, 85% high angle grain boundary, and high volume fraction of nanoscale (Ti,Mo)C precipitates. The microstructure continued to consist of ferrite when the PT was in the range of 650–1050 °C. However, the microstructure was altered to bainite with increase in the PT to 1350 °C. At PT of 650 °C, the precipitates were stable, while they coarsened at 850 °C, partially dissolved at 1050 °C, and completely dissolved at 1350 °C. The hardness of the subcritical HAZ was marginally decreased because of the addition of Mo, while the intercritical HAZ was softened because of coarsening of nanoscale precipitates. The transformation kinetics was related to prior austenitic grain size, change in C-content, which was controlled by the dissolution of (Ti,Mo)C precipitates, and supercooling.     

Martensitic transformation behaviors of rapidly solidified Ti–Ni–Mo powders

For the fabrication of bulk near-net-shape shape memory alloys and porous metallic biomaterials, consolidation of Ti–Ni–Mo alloy powders is more useful than that of elemental powders of Ti, Ni and Mo. Ti₅₀Ni_49.9Mo_0.1 shape memory alloy powders were prepared by gas atomization, and transformation temperatures and microstructures of those powders were investigated as a function of powder size. XRD analysis showed that the B2–R–B19 martensitic transformation occurred in powders smaller than 150 μm. According to DSC analysis of the as-atomized powders, the B2–R transformation temperature (T_R) of the 25–50 μm powders was 18.4 °C. The T_R decreased with increasing powder size, however, the difference in T_R between 25–50 μm powders and 100–150 μm powders is only 1 °C. Evaluation of powder microstructures was based on SEM examination of the surface and the polished and etched powder cross sections and the typical images of the rapidly solidified powders showed cellular morphology. Porous cylindrical foams of 10 mm diameter and 1.5 mm length were fabricated by spark plasma sintering (SPS) at 800 °C and 5 MPa. Finally these porous TiNi alloy samples are heat-treated for 1 h at 850 °C, and then quenched in ice water. The bulk samples have 23% porosity and 4.6 g/cm³ density and their T_R is 17.8 °C.     

High temperature tensile deformation behavior and failure mechanisms of an Al–Si–Cu–Mg cast alloy — The microstructural scale effect

In this study the high temperature tensile deformation behavior of a commercial Al–Si–Cu–Mg cast alloy was investigated. The alloy was cast with two different cooling rates which resulted in average secondary dendrite arm spacing of 10 and 25 μm, which is typical of the microstructure scale obtained from high pressure die casting and gravity die casting. Tensile tests were performed at different strain rates (10^− 4 s^− 1 to 10^− 1 s^− 1) and over a wide temperature range from ambient temperature to 500 °C. The fine microstructure had superior tensile strength and ductility compared to the coarse microstructure at any given temperature. The coarse microstructure showed brittle fracture up to 300 °C; the fracture mode in the fine microstructure was fully ductile above 200 °C. The fraction of damaged particles was increased by raising the temperature and/or by microstructure coarsening. Cracks arising from damaged particles in the coarse microstructure were linked in a transgranular-dominated fashion even at 500 °C. However, in the fine microstructure alloy the inter-dendritic fracture path was more prevalent. When the temperature was raised to 300 °C, the concentration of alloying elements in the dendrites changed. The dissolution rates of Cu- and Mg-bearing phases were higher in the fine microstructure.     

Effect of heat treatment and Fe content on the microstructure and mechanical properties of die-cast Al–Si–Cu alloys

The effect of solution and ageing heat treatment on the microstructure and mechanical properties of the die-cast Al–9 wt.%Si–3.5 wt.%Cu alloys containing 0.1–1.0 wt.% Fe was investigated. The results showed that the dendritic primary α-Al phase was varied from 20 to 100 μm in size and the globular α-Al grains were smaller than 10 μm in size. The Fe-rich intermetallics exhibited coarse compact or star-like shapes with the sizes from 10 to 20 μm and the fine compact particles at an average size of 0.75 μm. The solution treatment of the alloys could be achieved in a short period of time, typically 30 min at 510 °C, which dissolved the Cu-rich intermetallics into the primary α-Al phase and spheroidised the eutectic Si phase. During the subsequent ageing treatment, numerous fine precipitates of θ′ and Q′ phases were formed to provide effective strengthening to the α-Al phase, significantly improving the mechanical properties. Therefore, Fe content in the die-cast Al–Si–Cu alloys needs to be controlled at a low level in order to obtain the improved ductility and strength under solution and aged condition.     

Effects of copper addition on the in-situ synthesis of SiC particles in Al–Si–C–Cu system

In this research work, SiC particles have been successfully in-situ synthesized in Al–Si–Cu matrix alloy utilizing a novel liquid–solid reaction method. The effect of copper addition on the synthesis of SiC in Al–Si–C–Cu system was investigated. The composites mainly contain spherical SiC particles and θ-Al₂Cu eutectic phases, which are embedded in the α-Al matrix. Results indicated that the temperature for forming in-situ SiC particles significantly reduced from 750 °C to 700 °C with the copper addition. The size of in-situ synthesized SiC particles can be as low as 0.2 μm. Further study found that the addition of 10 wt.% copper into Al–Si–C alloy causes its solidus temperature to decrease by about 65 °C. Additionally, the Rockwell hardness value of SiCp/Al–18Si–5Cu composites has an average of 92, which is 50% higher than that of the sample without copper addition.     

Effect of microstructure and overaging on the tensile behavior at room and elevated temperature of C355-T6 cast aluminum alloy

The present study was focused on the microstructural and mechanical characterization of the Al–Si–Cu–Mg C355 alloy, at room and elevated temperature. In order to evaluate the influence of microstructural coarseness on mechanical behavior, samples with different Secondary Dendrite Arm Spacing (SDAS) (20–25 μm for fine microstructure and 50–70 μm for coarse microstructure), were produced through controlled casting conditions. The tensile behavior of the alloy was evaluated at T6 condition and at T6 with subsequent high temperature exposure (41 h at 210 °C, i.e. overaging), both at room and elevated temperature (200 °C). Microstructural investigations were performed through optical and electron microscopy.The results confirmed the important role of microstructure on the tensile behavior of C355 alloy. Ultimate tensile strength and elongation to failure strongly increased with the decrease of SDAS. Larger SDAS, related to lower solidification rates, modify microstructural features, such as eutectic Si morphology and size of the intermetallic phases, which in turn influence elongation to failure. Overaging before tensile testing induced coarsening of the strengthening precipitates, as observed by STEM analyses, with consequent reduction of the tensile strength of the alloy, regardless of SDAS. A more sensible decrease of tensile properties was registered at 200 °C testing temperature.     

Phase,microstructure and properties evolution of fine-grained W–Mo–Ni–Fe alloy during spark plasma sintering

Fine-grained tungsten (W) heavy alloy containing molybdenum (Mo) with W particle sizes of less than 5 μm were fabricated by spark plasma sintering (SPS) pre-milling W–2Mo–7Ni–3Fe powder at a lower temperature of 1000–1250 °C. Phase, microstructure and mechanical properties evolution of W–Mo–Ni–Fe alloy during spark plasma sintering were studied in detail. As increasing sintering temperature, the hardness of the alloy decreased rapidly. However, bending strength of the alloy demonstrated a fall–rise–fall trend, and the maximum strength was obtained at 1150 °C. The W–2Mo–7Ni–3Fe alloy microstructure was composed of white W-grain, gray W-rich structure, black γ-(Ni, Fe, W, Mo) binding phase, and deep-gray W-rich structure. The intergranular fracture along the W/W grain boundary is the main fracture modes of W–2Mo–7Ni–3Fe alloy.     

Experimental investigation and thermodynamic calculation of the phase equilibria in the Cu–Mo–Ni ternary system

The phase equilibria at 900 °C, 1000 °C, 1100 °C, 1200 °C and 1300 °C in the Cu–Mo–Ni system were experimentally determined by means of optical microscopy (OM), electron probe microanalyzer (EPMA) and X-ray diffraction (XRD) on the equilibrated alloys. The experimental results firstly found that the fcc-type miscibility gap exists at 900 °C, 1000 °C, 1100 °C and 1200 °C in the Cu–Mo–Ni system, and the solubility of Cu in the MoNi phase at 900 °C, 1000 °C, 1100 °C and 1200 °C are about 0.5 at.%, 1.5 at.%, 1.7 at.% and 4.0 at.%, respectively. The as-cast Cu₂₀Mo₂₀Ni₆₀ (at.%), Cu₂₀Mo₃₀Ni₅₀ (at.%), Cu₁₀Mo₆₀Ni₃₀ (at.%), Cu₇₀Mo₁₀Ni₆₀ (at.%), Cu₂₀Mo₆₀Ni₂₀ (at.%) and Cu₈₀Mo₁₀Ni₁₀ (at.%) alloys appear the separated macroscopic morphologies, which are caused by the liquid phase separation on cooling, while the as-cast Cu₁₀Mo₂₅Ni₆₅ (at.%), Cu₃₂Mo₅Ni₆₃ (at.%) and Cu_30.7Mo_6.3Ni₆₃ (at.%) alloys show the homogenous microscopic morphologies. On the basis of the experimental data investigated by the present and previous works, the phase equilibria in the Cu–Mo–Ni system were thermodynamically assessed by using CALPHAD (Calculation of Phase Diagrams) method, and a consistent set of the thermodynamic parameters leading to reasonable agreement between the calculated results and experimental data was obtained.     

Influence of evolving microstructure on magnetic-hysteresis characteristics in polycrystalline nickel–zinc ferrite,Ni0.3Zn0.7Fe2O4

We report some research findings on the parallel evolutions of microstructural properties and magnetic hysteresis-loop properties; we attempt to elucidate their relationships. The Ni_0.3Zn_0.7Fe₂O₄ toroidal samples were prepared via high-energy ball milling and subsequent moulding; the samples with nanometer/submicron sized compacted powder were sintered from 600 °C to 1400 °C using 100 °C increments. An integrated analysis of phase, microstructural and hysteresis data would point to the existence of three distinct shape-differentiated groups of B–H hysteresis loops which belong to samples with weak, moderate and strong magnetism. The observed grain size with respect to the magnetic-hysteresis behaviour varied from 0.19 μm to 0.23 μm, 0.24 μm to 0.43 μm and 1.07 μm to 4.98 μm for weak, moderate and strong ferromagnetic behaviour respectively. The first occurrence of a strikingly erect and well-defined sigmoid-shape was observable only when sufficient single-phase purity and crystallinity and a sufficiently high volume fraction of multi-domain grains (>0.25 μm) were attained.     

Diffusion bonding of 410 stainless steel to copper using a nickel interlayer

In the present work, plates of stainless steel (grade 410) were joined to copper ones through a diffusion bonding process using a nickel interlayer at a temperature range of 800–950 °C. The bonding was performed through pressing the specimens under a 12-MPa compression load and a vacuum of 10^? 4 torr for 60 min. The results indicated the formation of distinct diffusion zones at both Cu/Ni and Ni/SS interfaces during the diffusion bonding process. The thickness of the reaction layer in both interfaces was increased by raising the processing temperature. The phase constitutions and their related microstructure at the Cu/Ni and Ni/SS diffusion bonding interfaces were studied using optical microscopy, scanning electron microscopy, X-ray diffraction and elemental analyses through energy dispersive spectrometry. The resulted penetration profiles were examined using a calibrated electron probe micro-analyzer. The diffusion transition regions near the Cu/Ni and Ni/SS interfaces consist of a complete solid solution zone and of various phases based on (Fe, Ni), (Fe, Cr, Ni) and (Fe, Cr) chemical systems, respectively. The diffusion-bonded joint processed at 900 °C showed the maximum shear strength of about 145 MPa. The maximum hardness was obtained at the SS–Ni interface with a value of about 432 HV.     

Influence of heat treatment on microstructure and adhesion of Al2O3 fiber-reinforced electroless Ni–P coating on Al–Si casting alloy

Influence of heat treatment regime on microstructure, phase composition and adhesion of Al₂O₃ fiber-reinforced Ni–P electroless coating on an Al–10Si–0.3 Mg casting alloy is investigated in this work. The pre-treated substrate was plated using a bath containing nickel hypophosphite, nickel lactate and lactic acid. Al₂O₃ fibers pretreated with demineralised water were placed into the plating bath. Resulting Ni–P–Al₂O₃ coating thickness was about 12 μm. The coated samples were heat treated at 400–550 °C/1–8 h. LM, SEM, EDS and XRD were used to investigate phase transformations. Adhesion of coating was estimated using scratch test with an initial load of 8.80 N. It is found that annealing at high temperatures (450 °C and above) leads to the formation of hard intermetallic products (namely Al₃Ni and Al₃Ni₂ phases) at the substrate–coating interface. However, as determined by the light microscopy and by the scratch test, these phases reduce the coating adhesion (compared to coatings treated by the optimal annealing regime 400 °C/1 h). The analysis of scratch tracks proves that fiber reinforcement significantly reduces the coating scaling. However, due to the formed intermetallic sub-layers, partial coating delamination may occur on the samples annealed at 450 °C and above.     

An investigation of the effect of SiC particle size on Cu–SiC composites

In this study mechanical properties of copper were enhanced by adding 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles into the matrix. SiC particles of having 1 μm, 5 μm and 30 μm sizes were used as reinforcement. Composite samples were produced by powder metallurgy method and sintering was performed in an open atmospheric furnace at 700 °C for 2 h. Optical and SEM studies showed that the distribution of the reinforced particle was uniform. XRD analysis indicated that the dominant components in the sintered composites were Cu and SiC. Relative density and electrical conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Hardness of the composites increased with both amount and the particle size of SiC particles. A maximum relative density of 98% and electrical conductivity of 96% IACS were obtained for Cu–1 wt.% SiC with 30 μm particle size.     

Effects of rare earth La on microstructure and properties of Ag–21Cu–25Sn alloy ribbon prepared by melt spinning

Ag–21Cu–25Sn alloy ribbon as a promising intermediate temperature alloy solder (400–600 °C) was prepared by melt spinning technique in this paper. Rare earth La was added into Ag–21Cu–25Sn alloy to refine the microstructures and improve the wettabilities of as-prepared alloy solders. The phase constitutions, microstructures, melting temperatures and wettabilities of selected specimens were respectively tested. The results showed that the dominant phase constitutions of Ag–21Cu–25Sn–xLa alloy ribbons were Ag₃Sn and Cu₃Sn. The grain size of Ag–21Cu–25Sn–xLa alloy decreased with the addition of La increasing. La addition reduced the melting temperatures of Ag–21Cu–25Sn–xLa alloy ribbons, and effectively improved the wettabilities of the alloy ribbons. When the addition of La was 0.5 wt%, the wettability of as-prepared alloy solder achieved the optimal value of 158 cm² g⁻¹ under brazing temperature 600 °C and dwell time 15 min. In addition, raising brazing temperature and prolonging dwell time could improve the wettability of Ag–21Cu–25Sn–xLa alloy ribbon.     

Correlation between microstructure and tensile properties in powder metallurgy AZ91 alloys

The ultrafine-grained (0.3–1.3 μm) AZ91 alloys, which were fabricated by powder extrusion in the range of 200 to 350 °C and subsequent aging at 100 °C for 8 h, exhibit a remarkable yield stress of 360–478 MPa and moderate tensile elongations of 6–8%. A composite structure was developed after extrusion with uniform β (Mg₁₇Al₁₂) particles dispersed in magnesium matrix. The extrusion temperature has an indirect role on yield stress since partial dissolution of β particles induced by high extrusion temperature fails to retard grain growth. Moreover, the strength was further enhanced by the formation of nano-scale precipitates during artificial aging. The high strength could be attributed to a combination effect of grain refinement, particle reinforcement and precipitation hardening.     

Study on the microstructure and mechanical properties of diffusion brazing joint of C17200 Copper Beryllium alloy

In order to study the microstructure and mechanical properties of Copper Beryllium alloy, spreadability test was carried out at two temperatures under Argon atmosphere for different filler metals of Ag content. The results show that BAg2a (Ag–26Cu–21Zn–19Cd) and BAg1a (Ag–18.5Cu–17Zn–14.5Cd) are the best choice for brazing of Copper Beryllium. Zn affects the wetting of interlayer because it spreads preferentially. The bonding process was carried out at a temperature ranging of 650–800 °C for various times under Argon atmosphere using of BAg2a (Ag–26Cu–21Zn–19Cd) film with 100 μm thickness as interlayer.Interfacial microstructures were examined by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The eutectic and intermetallic compounds such as CuZn, AgZn3 and AgCd3 were formed at the interfaces between the interlayer and substrate. Microhardness and tensile tests were used for evaluating the mechanical properties. Average of hardness at the center of brazed seam decreased with increasing time and temperature that associated with diffusion of main elements to substrate and intermetallic formation at the interface. Maximum tensile strength of 170 MPa was obtained at 750 °C for 20 min for filler metal BAg2a without heat treatment and 227 MPa with heat treatment.     

A study on in situ growth of TaC whiskers in Al2O3 matrix powder for ceramic cutting tools

In situ growth of tantalum carbide (TaC) whiskers was synthesized in an α-Al₂O₃ matrix powder via a carbothermal reduction technique within a temperature range of 1350–1500 °C in an argon atmosphere. The starting materials consisted of Ta₂O₅, C, Ni and NaCl powders. Different mixing methods and various reaction temperatures were employed. Most of the prepared whiskers were 0.2–0.5 μm in diameter and 5–15 μm in length. The reaction temperature of 1400–1450 °C was suitable for the growth of TaC whiskers and a wet mixing method was beneficial to increase the whisker yield. Some of the whiskers exhibited the needle shape while others exhibited the screw shape. The growth mechanism of the whiskers was a complex mechanism involving a helical screw dislocation mechanism and a vapor–liquid–solid process. No obvious influences of the Al₂O₃ matrix powder on the growth of TaC whiskers were found and the major impurities in the obtained powder were TaC particles, nickel and unreacted carbon.     

Growth of SiC particles in reaction sintered SiC

For reaction sintered SiC (RSSC) prepared at 1600°C by conventional melt infiltration technique, experimentation with two different particle sizes of initial SiC, viz., 0.2 and 23.65 μm, showed that the large SiC particles remained unaltered and the sizes of the fine-grained SiC increased several times yielding well-developed faceted crystals in the final material. To study the process further, compacts of SiC powder of particle sizes varying between 0.20 and 8.99 μm were reacted with pure Si at 1600°C and the resulting SiC–Si boundaries were studied by optical microscopy. A distinct boundary layer with no penetration of Si in the compact of SiC of 0.2 μm was observed and the width of the SiC–Si boundary was found to be increasing linearly with time. Detailed SEM examination establishes the growth of the SiC upto around 4 μm from 0.2 μm starting powder. No such growth was observed in the case of starting SiC powder coarser than 0.2 μm. The growth of SiC is explained in terms of solution-reprecipitation mechanism.     

High temperature mechanical properties of low alloy steel foams produced by powder metallurgy

Cu–Ni–Mo and Mo based steel foams having different porosity levels for high temperature applications were produced by the space holder-water leaching technique in powder metallurgy. Steel powders were mixed with binder (polyvinylalcohol) and spacer (carbamide), and compacted. Spacer in the green compacts was removed by water leaching at room temperature and porous green compacts were sintered at 1200 °C for 60 min in hydrogen atmosphere. The successful application of foams at higher temperatures requires a good understanding of their high temperature mechanical properties. Compression tests were carried out on steel foams with different porosities at temperatures varying from room temperature to 600 °C in argon atmosphere. Effect of high temperature on compressive properties of the steel foams was investigated. It was found that the compressive strength of steel foams was greater at elevated temperatures than that at room temperature. This occurs across a range of temperatures up to 400 °C. Beyond this point the compressive strength decreased as the temperature increased. The reason for the enhancement of the compressive strength of Cu–Ni–Mo and Mo based steel foams is expected to be due to the effect of the dynamic age-hardening.