Wt Pct Ag Research Articles

Eutectic Solidification Morphologies in Rapidly Solidified Hypereutectic Sn–Ag Solder Alloy

The effect of rapid solidification upon hypereutectic Sn–Ag solder alloy has been investigated using a 6.5 m drop tube. Powder sizes ranging from > 850 to < 38 μm were produced, with equivalent cooling rates of 250 to 14,800 K s−1 for 850 and 38 μm droplets, respectively. At all cooling rates investigated, dendritic β-Sn was observed as the primary solidification phase, not proeutectic Ag3Sn as predicted by the phase diagram. The volume fraction of interdendritic eutectic was observed to decrease with increasing cooling rate, with the Ag concentration in the residual interdendritic liquid estimated at 12.5–15 wt pct Ag, far in excess of the eutectic concentration of 3.8 wt pct. Much of the Ag3Sn observed within the eutectic had a blocky, divorced eutectic appearance. A model is proposed which can explain these observations in terms of sluggish nucleation of the Ag3Sn intermetallic, coupled with a metastable phase diagram that permits significant supersaturation of Ag at modest undercooling.

Influence of Ir Additions and Icosahedral Short Range Order (ISRO) on Nucleation and Growth Kinetics in Au-20.5Wt Pct Cu-4.5Wt PctAg Alloy

Based on detailed EBSD analyses, Kurtuldu et al. (Acta Mater. 70:240–248, 2014) have explained the grain refinement of Au-12.5 wt pctCu-12.5 wt pctAg (yellow gold) by the addition of minute amounts of Ir in terms of “icosahedral quasicrystal (iQC)-mediated nucleation”, i.e., Ir induced the formation of Icosahedral short range order (ISRO) of atoms in the liquid, leading to the formation of iQC on which the fcc-phase forms. In the present contribution, we show that: (i) this mechanism is also responsible of the grain refinement in Au-20.5 wt pctCu-4.5 wt pctAg (pink gold) with Ir addition; (ii) ISRO also influences the morphology and growth kinetics of the fcc phase: at solidification rate of a few mm/s, $$\langle 100\rangle $$ dendrites are replaced by a cellular-type morphology growing along $$\langle 111\rangle $$ when 100 wt ppm of Ir is added to the melt; (iii) iQC-mediated nucleation is accompanied by a spinodal decomposition of the liquid, which is revealed at high cooling rate by the formation of Cu-rich particles or dendrites, some of them being also twinned, in parallel to iQC-mediated grain refinement and twin formation.

Direct Observation of Pure Cu and Cu-Ag Anode Passivation in H2SO4-CuSO4 Aqueous Solution by Channel Flow Double Electrode and Optical Microscopy

The dissolution and passivation of pure Cu and Cu-5 wt pct Ag anodes in H2SO4-CuSO4 electrolyte were investigated by a direct observation method that combined the techniques of optical microscopy and channel flow double electrode. Linear sweep voltammetry of the anodes showed that the dissolution of Cu transited from the charge transfer-controlled reaction to the mass transfer-controlled reaction, followed by the passivation of the electrodes. The direct observation of the pure Cu anode revealed that Cu particles were generated on the surface and the particles fell away during passivation. On the other hand, a slime layer of Ag particles that adhered to the surface was generated during the dissolution of the Cu-5 wt pct Ag anode. The Cu-5 wt pct Ag anode was passivated with a lower current density than the pure Cu anode, which suggested that the morphology and adhesive characteristics of the slime on the anode affected the passivation. The direct observation method described herein is useful for understanding reactions on electrodes that undergo drastic changes in their surface morphology. Information obtained from this method can help with the development of new processes for the effective utilization of limited natural resources and energy, such as the recycling of Cu by electrorefining.

Microstructural and Hardness Evaluations of a Centrifuged Sn-22Pb Casting Alloy Compared with a Lead-Free SnAg Alloy

A great preoccupation with replacing the traditional Sn-Pb alloy with a Pb-free alloy (“green alloy”) is recognized. There are industrial sectors that demand metallurgical improvements to attain certain unsoundness and adequate properties as a function of imposed operational parameters. In this experimental investigation, two distinctive centrifuged casting alloys (i.e., Sn-2 wt pct Ag and Sn-22 wt pct Pb) are compared. It is found that centrifuged castings have similar microstructure constituents, although distinctive cooling rates and solute contents are considered. It is also found that Ag3Sn intermetallic particles are responsible for attaining similar tensile strength, since more dislocations between Ag3Sn particles and the Sn-rich phase are provided. In order to replace the Sn-Pb alloys with a successor alloy containing sustainability and environmental aspects associated with castability and to guarantee the desired properties, it seems that a green alloy (Pb free) with intermetallic particles finely and homogeneously distributed provides an interesting benefit to various industrial applications.

Distribution of Precious Metals (Ag, Au, Pd, Pt, and Rh) Between Copper Matte and Iron Silicate Slag

The distributions of precious metals (Ag, Au, Pd, Pt, and Rh) between copper matte and silica-saturated iron silicate slag were determined at 1523 K to 1623 K (1250 °C to 1350 °C), in controlled CO-CO2-SO2-Ar gas mixtures. The experiments were done in silica crucibles and a fixed partial pressure of sulfur dioxide for matte grades of 55, 65, and 75 wt pct Cu. High-temperature equilibration/quenching/electron probe X-ray microanalysis technique was used to obtain compositions of the equilibrated matte and slag. The technique was applied for the first time to the distributions of precious metals in simulated flash smelting conditions. The resolution of electron probe microanalysis became critical as the detection limits were insufficient to measure reliably the precious metals concentrations (except silver) in the slag. The distribution coefficient of silver, L m/s[Ag] = [wt pctAg in matte]/(wt pctAg in slag), was found to be between 200 and 300, which agrees well with the latest studies in the literature. For other precious metals, the minimum values of distribution coefficients were determined according to the detection limits in the slag. The values obtained were for gold and platinum >250, for palladium >1000, and for rhodium >900. The distribution coefficients of palladium, although locating above distribution coefficient of the detection limit, formed a clear dependency with a good repeatability as a function of the matte grade. It increased along with matte grade and was approximately 1000 at 50 pct Cu and 2000 to 3000 at 70 pct Cu. The precious metals replace metal in the matte structure and they are present as sulfides in the copper matte.

Electrochemical and Mechanical Behavior of Lead-Silver and Lead-Bismuth Casting Alloys for Lead-Acid Battery Components

The present study focuses on the interrelation of microstructure, mechanical properties, and corrosion resistance of Pb-Ag and Pb-Bi casting alloys, which can be used in the manufacture of lead-acid battery components, as potential alternatives to alloys currently used. A water-cooled solidification system is used, in which vertical upward directional solidification is promoted permitting a wide range of microstructures to be investigated. Correlations between microstructural arrays, tensile strengths, and corrosion resistances of Pb-1 wt pct Ag, Pb-2.5 wt pct Ag, Pb-1 wt pct Bi, and Pb-2.5 wt pct Bi alloys are envisaged. It is shown that a compromise between corrosion resistance (represented by the corrosion current density) and mechanical properties (represented by the ultimate tensile strength) can be obtained. Comparisons between specific strengths and mechanical/corrosion ratios are also made. It is also shown that, for microstructures solidified under cooling rates higher than 10 K/s, the Pb-Ag alloys exhibit higher specific strength and mechanical/corrosion ratio. In contrast, for casting processes in which the cooling rates are lower than 5 K/s, the dilute Pb-Bi alloy (i.e., 1 wt pct Bi) is shown to have more appropriate requirements for lead-acid battery components. Comparisons between specific strengths, mechanical/corrosion ratio, and relative weight and cost with Pb-Sn and Pb-Sb alloys are also made.

Unusual Morphological Evolution of the Cu Pillar/Solder Micro-joints During High-Temperature Annealing

The morphological evolution of Cu pillars capped with Sn-1.8 wt pct Ag solder during high-temperature annealing was investigated. Two intermetallic compounds (Cu6Sn5 + Cu3Sn) formed at the Cu/solder interface which changed the pillar’s morphology. Surface diffusion enhanced the growth of Cu6Sn5 + Cu3Sn around the pillar brim and transformed the pillar top from a plane into a truncated cone. Bulk diffusion dominated after long-term annealing and the pillar top became hemispherical shaped. A mechanism was proposed to explain the unusual morphological evolution.

The Structure and Kinetics of the Nanoscale Precipitation Processes in Al-1.0 wt pct Mg2Si-0.4 wt pct Mg-0.5 wt pct Ag Alloy

The influence of addition of 0.4 wt pct Mg on the precipitation sequence in the balanced Al-1.0 wt pct Mg2Si bearing 0.5 wt pct Ag has been investigated during the continuous heating of the quenched alloy from the solid solution state. Differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy techniques have been used. The DSC experiments showed that all processes occurred are thermally activated. The activation energies of the precipitation processes have been determined and hence the kinetics of these precipitates have been determined. The obtained results have shown that the existence of excess Mg inhibits the formation of the early stage clusters of solute-vacancy clusters. These clusters can be assisted by the binding energies between solute Si, Mg, and Ag atoms and the excess vacancies. On the other hand, excess Mg accelerates the precipitation of random, β′-phase and β-phase precipitates.

Enhancement of Strength and Ductility of Al-Ag Alloys Processed by High-Pressure Torsion and Aging

This research was conducted by the application of high-pressure torsion (HPT) to Al-X wt pct Ag alloys (X = 5, 11, 20). Grain refinement was achieved to the size of ~300 nm after HPT processing at room temperature. The aging behavior of the alloys after HPT processing was investigated using Vickers microhardness measurement, tensile testing, scanning electron microscopy, and transmission electron microscopy. This study confirms the dual effect of grain refinement and fine precipitation on the enhancement of the strength. It is also shown that at peak-aged condition, the tensile strength is enhanced while maintaining considerable ductility.

Quantitative analysis of work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy based on true stress vs strain curves

Quantitative analysis of work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy based on true stress vs strain curves

Influence of External Stress on Discontinuous Precipitation Behavior in a Cu-Ag Alloy

The influence of an applied stress on discontinuous precipitation (DP) has been investigated for a Cu-5 wt pct Ag alloy aged at 573 K. A tensile stress enhances the growth of DP cells in both the loading direction (LD) and transverse direction (TD), but the cell growth rate in the TD, v CT , is faster than that in the LD, v CL . A compressive stress suppresses the cell growth in the TD, but does not significantly influence it in the LD. The tensile or compressive stress tends to produce discontinuous silver precipitates elongated in a $$ \left\langle {110} \right\rangle_{\alpha } $$ direction of the copper matrix in a DP cell, nearly perpendicular to or parallel to the LD. This result, along with the dependence of the cell growth rate on the sense of the applied stress, can be understood through the interaction energy between the external stress and the misfit strains of silver precipitates. An analysis of length-change measurement results has enabled estimation of the ratio of the growth rate of silver precipitates in the TD, v PT , to that in the LD, v PL , under tension or compression. The estimated values of v PT /v PL are in good agreement with the values of v CT /v CL , experimentally obtained, indicating that the anisotropy of the cell growth rate is determined by the growth behavior of silver precipitates.

Effects of Route on Microstructural Evolution and Mechanical Properties of Cu-8 Wt Pct Ag Alloy Processed by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) is applied to investigate the microstructural evolution and mechanical properties of Cu-8 wt pct Ag alloy subjected to one to four passes via four different routes (A, B(A), B(C), and C). It is demonstrated that better mechanical properties, a higher fraction of high-angle boundaries, and a smaller grain size can be obtained most rapidly with route A, whereas the specimen processed by route B(C) contains relatively inhomogeneous microstructure and has poor mechanical properties. The ultimate tensile stress (UTS) of the Cu-Ag alloy processed by route B(C) saturates after four passes; in contrast, the UTS of the Cu-Ag alloy processed by route A increases continuously in relation to the number of ECAP passes. Based on the experimental results, the strengthening mechanisms of the Cu-8 wt pct Ag alloy processed by different routes as well as the efficiency of different routes in refining the binary alloy are discussed.

Tin-silver-copper eutectic temperature and composition

A careful investigation of the Sn-Ag-Cu phase diagram near the ternary eutectic composition was undertaken using annealed alloys and differential scanning calorimetry to settle some uncertainties in the eutectic composition. The eutectic composition was found to be 3.5 wt pct Ag, 0.9 wt pct Cu, and the balance Sn. The published eutectic temperature, 217 °C, was confirmed. A value of 217.2 °C was obtained in the present research.

Dissolution kinetics of Widmanstätten γ-Ag2AI precipitates

A combination of scanning electron microscope and electron probe studies has been conducted on the dissolution of Widmanstatten γ-Ag2Al plates in Al-15.3 wt pct Ag alloys between the temperatures of 466 °C and 494 °C. Individual rather than averaged kinetic events have been monitored in all cases. The kinetics at the tip were observed to be linear with time and at the broadface to be parabolic with time. The broadface kinetics were slower than expected for volume diffusion control. Electron probe measurements round the dissolving precipitate gave similar diffusion profiles at the tip and the broadface. These indicated a slower dissolution rate at the tip than observed experimentally and a faster rate at the broadface than observed experimentally. A mechanism to explain the discrepancy between the kinetic and probe results is suggested.

An AEM investigation of the formation of precipitate-free zones in an AI-16 Wt Pct Ag alloy: Determination of equilibrium and metastable solvus lines

Precipitation of the equilibrium y-phase at grain boundaries in an aged Al-16 wt pct (∼4.5 at. pct) Ag alloy is responsible for the formation of a solute depleted region, free of metastable Guinier-Preston (GP) zones, in the immediate vicinity of the grain boundary. Solute concentration profiles have been obtained across these grain boundary regions using Analytical Electron Microscopy (AEM) in thin foils of the alloy aged at low temperatures. The Ag concentrations at the grain boundary (between γ precipitates) and at the edge of the precipitate-free zone have been used to determine the solid solubility of Ag in Al (the α/(α + γ) solvus) and the metastable GP zone solvus line, respectively.

Further observations on the formation mechanisms of precipitate-free zones in an aged AI-16 wt pct ag alloy

In summary solute diffusion effects can describe the presence of asymmetric solute concentration profiles and asymmetric PFZ around grain boundaries in an aged Al-16 wt pct Ag alloy. These effects are also responsible for the lack of precipitate (..gamma..) coarsening and cause reprecipitation during the initial aging treatment.

Macrosegregation in castings rotated and oscillated during solidification

The macrosegregation present in stationary, rotated, and oscillated castings of Al-3 wt pct Ag was determined by measuring the distribution of radioactive silver added to the melt. Considerable scatter was observed in the measurements, the scatter being dependent on the sampling technique used. It was found that no significant macrosegregation was present in the stationary and rotated castings. Extensive macrosegregation was detected in the oscillated casting. For the oscillating case the macrosegregation can be accounted for on the basis of the long range movement of dendrite fragments which break and/or melt off in the solid-liquid interface region. This movement is a direct result of turbulent waves associated with the oscillation. The maximum silver concentration is shown to be related to the columnar-to-equiaxed transition.