Influence of minor additions on characteristics of Cu–Al–Ni alloy

Abstract

The aluminium and nickel contents of Cu–Al–Ni alloy are varied to relate the parent phase chemistry to its shape memory behaviour. Rare earth and grain refining elements (titanium, zirconium, boron, etc.) are added in minor quantities to assess their effects on the grain refinement of the alloy and also on its shape recovery behaviour. It is observed that increasing the aluminium and nickel contents decreases the shape recovery temperature whereas minor additions are found to increase it. The alloys have been aged in the parent as well as the martensitic phase to investigate the influence of minor additions on their aging response. It is observed that precipitation of γ₂ phase occurs during the initial stage of aging of the ternary alloy. The aging behaviour is monitored via changes in resistivity and hardness of the alloys during aging. Minor additions are found to retard the precipitation of γ₂ phase during aging. Titanium and rare earths particularly reduce the tendency for grain coarsening in the alloy. It is further observed that two types of martensite, β′₁ and γ′₁, are produced in the alloys under investigation. The transformation temperatures of these martensites are also related to the aluminium content of the alloy.

MST/1744     

Influence of minor POSS molecules additions on the microstructure and hardness of Sn3Ag0.5Cu–xPOSS composite solders

The influence of minor POSS (polyhedral oligomeric silsesquioxanes) molecules additions on the microstructure and hardness of SnAgCu–xPOSS (x?=?1, 3 and 5) was investigated. A mechanical mixture method was adopted by adding POSS molecules as dispersoids into SnAgCu solder to fabricate SnAgCu–xPOSS composite solders. The microstructural evolution and the hardness of the solders were investigated in details by microstructural observations, Vickers hardness tester and nanoindentation tests. The results showed that the effects of the dispersed POSS molecules in eutectic SnAgCu structure and the refined Ag₃Sn IMC particles increased the hardness of eutectic SnAgCu phase and then increased the hardness of composite solder. In addition, because of the agglomeration of POSS molecule, a coarse lath-shaped structure (composed of POSS molecules, Ag₃Sn phase and minor Cu₆Sn₅ phase) formed in SnAgCu–5POSS solder matrix, which reduced the hardness of SnAgCu–5POSS solder.     

Influence of small Sb nanoparticles additions on the microstructure, hardness and tensile properties of Sn–9Zn binary eutectic solder alloy

In the present study, different weight percentages of Sb nanoparticles (100–120 nm) ranging from 0 to 1.5 wt% were added to Sn–9Zn eutectic solder alloy to investigate the effect of third element addition on the microstructure, mechanical properties as well as thermal behavior of the newly developed composite solder alloys. The results indicate that the Sb nano-particle based intermetallic compounds (IMC) were found uniformly distributed, refined the microstructure and formed IMC particles in the eutectic solder alloy. After the addition of nano Sb particles in Sn–9Zn solder, fine α-Zn phase and ε-Sb₃Zn₄ IMC particles were clearly observed in the β-Sn matrix. The ε-Sb₃Zn₄ IMC particles were uniformly distributed in the β-Sn phase, which resulted in an increase in the tensile strength due to the second phase dispersion strengthening mechanism. However, in the doped Sn–9Zn/1.5Sb alloys, α-Zn phases were broken enormously, depleted and round shaped compared to the normal rod shaped α-Zn phase microstructure in plain Sn–9Zn solder. In comparison, the ε-Sb₃Zn₄ IMC particle in the doped Sn–9Zn/1.0Sb alloy were star shaped. The average tensile strength and micro-hardness of the Sb doped Sn–9Zn solder alloys were consistently higher than the plain un-doped Sn–9Zn solder. The tensile strength and the microhardness increased with increasing Sb nano-particle content, up to 1.0 wt% of Sb content, and then decreased beyond that threshold value. Consequently the percentage (%) elongation of the Sb nanoparticle doped Sn–9Zn solder decreased with increasing Sb nano-particle content, up to 1.0 wt% of Sb content, and then increased beyond that threshold value.     

Effect of ZnO nanoparticles addition on thermal, microstructure and tensile properties of Sn–3.5 Ag–0.5 Cu (SAC355) solder alloy

Regarding to the development of Sn–Ag–Cu (SAC) lead-free solders for advance electronic components, the effect of 0.5 wt% nano-sized ZnO particles on the thermal, microstructure and tensile properties of Sn–3.5 wt% Ag–0.5 wt% Cu (SAC355) lead-free solder alloy is investigated. The results showed that addition of 0.5 wt% nano-sized ZnO particles into the conventional lead-free SAC355 solder caused a slight increase of its liquidus temperature by about 1.1 K. Metallographic observations of SAC355–0.5 wt% ZnO (composite solder) revealed an obvious refinement in the microstructure compared with the SAC355 (non-composite) solder. Consequently, addition of nano sized-ZnO particles could improve the stress–strain characteristics proof stress (σ_y0.2) and ultimate strength (σ_UTS). This was rendered to suppressing effect of ZnO on the coarsening of the intemetallic compounds (IMCs) Ag₃Sn and Cu₆Sn₅ during the solidification process in the composite solder and subsequently dispersion strengthening is considered to be the dominating mechanism. This will allow the use of SAC355 composite lead-free solder alloy, to be consistent with the conditions of usage for conventional SAC solder alloys and to overcome the serious problem of the excessive growth of IMCs and the formation of microvoids in the SAC lead-free solder alloys.     

Effects of Ga–Ag, Ga–Al and Al–Ag additions on the wetting characteristics of Sn–9Zn–X–Y lead-free solders

The effects of Ga–Al, Ga–Ag and Al–Ag binary additions on the wetting characteristics of Sn–9Zn–X–Y lead-free solders are studied by the wetting balance method. Experimental results show that Sn–9Zn–1.0Ga–0.3Ag, Sn–9Zn–0.005Al–0.3Ag, and Sn–9Zn–0.3Ga–0.002Al possess better wettability than the other alloys tested. The mechanism by which Ga, Al, and Ag additions improve the wettability is also proposed. It appears that dense aluminum oxide film formation and the enrichment of Ga on the surface may protect the bulk liquid solder from further oxidation. Moreover, results also indicate that, AgZn₃ IMCs layer formed at the interface, which may release reaction energy during the wetting, results in improving the wettability of the solder.     

Effects of TiO2 nanoparticles addition on microstructure,microhardness and tensile properties of Sn–3.0Ag–0.5Cu–xTiO2 composite solder

The effects of TiO₂ nanoparticles addition on the microstructure, microhardness, and tensile properties of Sn–3.0 wt.%Ag–0.5 wt.%Cu–x wt.%TiO₂ (x = 0, 0.05, 0.1, and 0.6) composite solders were systematically investigated. Scanning electron microscope (SEM) was used to observe the microstructural evolution of the composite solders, measure the size of the Ag₃Sn grains, and estimate the spacing between the Ag₃Sn grains in the solder matrix. Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD) were used to identify the phases of eutectic areas in the composite solder matrix. Results show that both the average size of Ag₃Sn grains and the spacing between the Ag₃Sn grains decrease significantly, which might owe to the strong adsorption effect and high surface free energy of the TiO₂ nanoparticles. The microhardness is improved by 37% compared with TiO₂-free noncomposite solder as the weight percentage of TiO₂ nanoparticles is 0.1 wt.%. The improvement is due to the microstructural change of the composite solders, which is in good agreement with the prediction of the classic theory of dispersion strengthening. Tensile tests reveal that the TiO₂-containg composite solder alloys have higher ultimate tensile strength (UTS) than TiO₂-free noncomposite solder alloy due to solid solution hardening. UTS of solder alloys have a logarithmic increase relation with strain rate ranging from 10⁻³ s⁻¹ to 10⁻¹ s⁻¹ and decreases with an increase of test temperatures ranging from 25 °C to 125 °C.     

Effects of nano-structured particles on microstructure and microhardness of Sn–Ag solder alloy

In this research, the typical nano-structured Polyhedral Oligomeric Silsesquioxane (POSS) particles were incorporated into the Sn–3.5Ag eutectic solder paste by mechanically mixing to form lead-free composite solder. The effects of nano-structured POSS additions on the microstructure and mechanical properties of as-fabricated composite solder alloys were systematically investigated. Experimental results indicated that the average size and spacing distance of Ag₃Sn intermetallic compounds (IMCs) in composite solder matrix decreased as compared to the Sn–3.5Ag eutectic solder. The 3 wt% addition of nano-structured POSS particles could enhance the microhardness of composite solder by 18.4% compared with the Sn–3.5Ag eutectic solder matrix. The average grain size and spacing distance of Ag₃Sn IMCs in Sn–Ag + 3 wt% POSS composite solder matrix reduced from 0.35 to 0.23 μm and from 0.54 to 0.32 μm, respectively. The refined Ag₃Sn IMCs, acting as a strengthening phase in the solder matrix, could enhance the microhardness of the composite solders.     

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.     

Influence of Sc and Zr additions on microstructure and properties evolution of Al–Zn–Mg alloy

Journal of Materials Science - In this study, the effects of different Sc?+?Zr compound addition on the tensile properties, impact toughness, stress corrosion cracking (SCC) properties,...     

Effects of minor additions of Ce and Y on as cast microstructure of Mg–3Sn–2Ca magnesium alloy

Abstract

The effects of minor additions of Ce and Y on the as cast microstructure of Mg–3Sn–2Ca (wt-%) magnesium alloy are investigated and compared. Results indicate that adding minor Ce or Y to Mg–3Sn–2Ca alloy does not cause formation of any new phases in the alloy. The as cast Mg–3Sn–2Ca alloy with addition of 0·5 wt-%Ce or Y is still composed of α-Mg, CaMgSn and Mg₂Ca phases. However, after adding 0·5 wt-%Ce or Y to Mg–3Sn–2Ca alloy, not only the formation of CaMgSn phase in the alloy is suppressed but also the CaMgSn phases in the alloy are effectively refined. In addition, adding 0·5 wt-%Ce to Mg–3Sn–2Ca alloy exhibits higher refinement efficiency to the CaMgSn phase in the alloy than adding 0·5 wt-%Y. Further investigations need to be considered in order to understand the difference of minor Ce and Y with regard to the refinement of CaMgSn phase in the Mg–3Sn–2Ca alloy.     

Effect of microstructure and Ag3Sn intermetallic compounds on corrosion behavior of Sn–3.0Ag–0.5Cu lead-free solder

In this paper, the effects of microstructure on the corrosion behavior of Sn–3.0Ag–0.5Cu (SAC305) lead-free solder were investigated by potentiodynamic polarization and atmospheric corrosion test. Scanning electron microscopy and X-ray diffraction were used to characterize the samples after the electrochemical and atmospheric corrosion tests. Results showed that commercial SAC305 solder exhibits better corrosion resistance than air-cooled and furnace-cooled SAC305 solders both in 3.5 wt% NaCl solution and at 60 °C/100 % relative humidity condition.     

Effect of zinc additions on structure and properties of Sn–Ag eutectic lead-free solder alloy

The effects of a third element, i.e., Zn in the range of 0.5–2.5 wt.%, on structure and properties of the binary Sn–Ag eutectic lead-free solder alloy were investigated. To identify the structure of the resulting alloys, X-ray diffraction analysis has been carried out. Resistivity, contact angles, Vickers microhardness and Young’s modulus have been measured. The results showed that all Zn contents were restricted in formation of Ag-Zn compound indicated by X-ray diffraction peaks, which increased continuously in the number and intensity as Zn content increased. Adding Zn up to 1.5 wt.% improved the wetting and mechanical properties. Above that, wetting angle increased due to the increase in AgZn compound, which may accumulated at the interface between solders and copper- substrate resulting a decrease in the adhesive strength. The alloy of composition Sn-3.5Ag-1.5Zn has the most improved properties between the others.     

Effect of trace additions of Sn on microstructure and mechanical properties of Al–Cu–Mg alloys

The work is aimed at investigating the influence of trace additions of Tin (Sn) on the microstructure, mechanical properties and age-hardening behavior of Al–6.2%Cu–0.6%Mg alloy system. Al–6.2%Cu–0.6%Mg alloys containing varying weight percentages (from 0 to 0.1 wt.%) of Sn were prepared by casting technique. The mechanical properties and microstructure of these alloys were investigated in the as-cast as well as different heat treated conditions. The composition of the different phases present in the microstructure was determined by energy dispersive X-ray (EDS) analysis. The average grain size of the annealed alloy was found to be maximum with trace content of 0.06 wt.% Sn. The hardness and strength of the alloy increased but the ductility reduced with increase in Sn content up to 0.06 wt.%. Precipitation hardening behavior of the alloys was investigated by analyzing the aging time required to attain the peak hardness value. Addition of trace percentage of Sn was observed to have no significant influence on the peak ageing time of the investigated alloy system.     

Effect of Al on the microstructure and properties of Sn–0.7Cu solder alloy

Effect of Al on the microstructure and mechanical properties were investigated. The results showed that Al could depress the formation of eutectic phase in Sn–Cu–Al solder alloy. The intermetallic compounds of Sn–0.7Cu–0.03Al were refined compared with that of Sn–0.7Cu–0.015Al. Segregated CuAl intermetallic compound was observed in Sn–0.7Cu–0.15Al and Sn–0.7Cu–0.5Al solder alloy. Sn-whisker was observed on the polished surface of Sn–0.7Cu–0.15Al and Sn–0.7Cu–0.5Al. The ultimate tensile strength of Sn–0.7Cu–0.03Al and Sn–0.7Cu–0.5Al was found to be higher than that of Sn–0.7Cu–xAl (x = 0, 0.015 and 0.15). The elongation of Sn–0.7Cu–0.015Al was the highest. The creep performance of Sn–0.7Cu–0.03Al and Sn–0.7Cu–0.5Al was similar and higher than that of Sn–0.7Cu and Sn–0.7Cu–0.15Al.     

Combined effects of Ag content and cooling rate on microstructure and mechanical behavior of Sn–Ag–Cu solders

Sn–0.7 wt%Cu–1.0 wt%Ag and Sn–0.7 wt%Cu–2.0 wt%Ag alloys were directionally solidified under transient conditions undergoing cooling rates varying from 0.1 to 25 K/s. The microstructure was characterized along the castings lengths and the present experimental results include the secondary dendrite arm spacing (λ₂) and its correlation with: the tip cooling rate ($\dot{T}$) during solidification and microhardness (HV), yield tensile strength (σ_y), ultimate tensile strength (σ_u) and elongation to fracture (δ). The aim is to examine the effects of Ag content and tip cooling rate on both the microstructure and mechanical properties. The initiation of tertiary branches within the dendritic arrangement, as well as the distinct morphologies of the intermetallic compounds (IMC) related to the solidification cooling rate was also assessed for both examined alloys. While the Cu₆Sn₅ phase appeared as large faceted crystals along the entire casting length, very fine Ag₃Sn spheroids prevailed at higher cooling rates (>7.5 K/s and > 4.0 K/s for 1.0 wt%Ag and 2.0 wt%Ag alloying, respectively) with a mixture of Ag₃Sn coarser spheroids and fibers predominating at lower cooling rates. The Sn–0.7 wt%Cu–2.0 wt%Ag alloy exhibited smaller dendritic spacings and HV of about two times higher than the corresponding values of the Sn–0.7 wt%Cu–1.0 wt%Ag alloy. A single Hall–Petch equation is proposed relating δ to λ₂ for both alloys, which means that the increase in Ag content from 1.0 to 2.0 wt% does not affect the elongation. It is shown that δ decreases with the increase in λ₂.     

Influence of hot pressing temperature on the microstructure and mechanical properties of 75% Cu–25% Sn alloy

The alloy of 75% Cu–25% Sn was utilised and hot-pressed for 4 min at 421, 520 and 600 °C to obtain a self-sharpening bond for diamond honing stones at low sintering temperature. Densification and mechanical tests were performed, and structures were investigated by X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. Results showed that the porous structures changed into microporous structures when the hot pressing temperature was increased from 421 °C to 600 °C. The mechanical properties improved from HRB 79.1 to HRB 105.1 in hardness and from 104.2 MPa to 201.4 MPa in transverse rupture strength. After hot pressing at 600 °C, the microstructure consisted of α(Cu) + δ eutectoid and micropores, which meets the requirements of bonds for honing stones.     

Effects of Ga addition on microstructure and properties of Sn–0.5Ag–0.7Cu solder

The effects of rare element Ga on solderability, microstructure, and mechanical properties of Sn–0.5Ag–0.7Cu lead-free solder were investigated. The experimental results show that Ga plays a positive role in improving the wettability and the microstructure of the solder. When the content of Ga is at 0.5 wt%, the grain size of the solder is smaller and the shear force is enhanced greatly. It is also found that the thickness of the IMCs at the solder/Cu interface is reduced with proper addition of Ga. The increase of mechanical properties may be related to the refining of IMCs of the solder due to Ga addition.     

Effect of tin on melting temperature and microstructure of Ag–Cu–Zn–Sn filler metals

Abstract

To develop low melting point filler metals for brazing TiNi shape memory alloy (SMA) and stainless steel (SS), a series of Ag–22Cu–Zn–Sn (wt-%) filler metals have been studied. Using differential thermal analysis (DTA) analysis, the melting temperatures of Ag–22Cu–Zn–Sn filler metals were determined. The results show that the increase of zinc and tin contents drastically decreases the solidus and liquidus temperatures of the Ag–22Cu–Zn–Sn filler metals and the melting temperatures of the Ag–22Cu–18Zn–Sn filler metals with 5–8 wt-%tin are < 650°C. Metallographic observations indicate that the increase of zinc and tin in the Ag–22Cu–Zn–Sn filler metals helps the formation of eutectic structure and inhibits the formation of α-Ag and α-Cu solid solutions, but the increase of tin also causes the formation of Ag₃Sn and Cu₄₁Sn₁₁ brittle compounds. The results of mechanical property tests of the laser brazed joints of TiNi SMA and SS show that the proper increase of zinc and tin in Ag–22Cu–Zn–Sn filler metals is favourable for improving the strength of the laser brazed joints of TiNi SMA and SS.     

Influence of quenching rate on microstructure and dimensional stability of Al–Cu–Mg–Si alloy

With the development of precision instrument in space industry fields, increasing attention has been devoted to improve the dimensional stability of structural materials. In this study, the influence of quenching rate on microstructure, residual stress and dimensional stability of Al–Cu–Mg–Si alloy was studied. The results showed that boil water quenching resulted in very low residual stress but unsatisfactory mechanical properties. In contrast, low residual stress and good mechanical property were achieved by quenching the sample into 80°C water. Residual stress has a significant influence on the thermal dimensional stability. The thermal dimensional stability of sample quenched in 80°C water is better than that of sample quenched in 20°C water due to lower residual stress in 80°C water-quenched sample.     

Influence of sulphur on the microstructure and properties of Ag–Cu–Zn brazing filler metal

Abstract

The effect of sulphur on the microstructure and properties of Ag45–Cu30–Zn25 brazing filler metal was investigated. Under the given experimental conditions, the sulphuration products mainly consisted of CuS, ZnS, Ag₂S, Cu₂S and Ag₃CuS₂. These sulphides not only distributed on the surface but also diffused into the interior of the filler metal and cut apart the matrix thereby significantly damaging the tensile strength of the filler metal from 658 to 283 MPa. The corresponding fracture characterisation turned from ductile fracture to brittle fracture. The sulphides existed as solid particles, which hinder the spreading of the liquid filler metal and the spreading area dramatically decreased from 317?09 to 18?55 mm², which indicates that the filler metal rarely wets the base metal.