L. C. Tsao

Active Soldering of Indium Tin Oxide (ITO) With Cu in Air Using an Sn3.5Ag4Ti(Ce, Ga) Filler

Indium tin oxide (ITO) ceramics are bonded with ITO and Cu at 250 °C in air using an active solder Sn3.5Ag4Ti(Ce, Ga). The mechanism for such low temperature soldering of ITO ceramics in air has been investigated. Electron probe microanalyzer (EPMA) analyses reveal that the element oxygen distributes uniformly within the solder matrix after soldering, while Ti segregates effectively at the ITO/solder and Cu/solder interfaces at such a low temperature, giving satisfactory joining results of Cu/Cu, ITO/ITO, and ITO/Cu in air.

Effects of zinc additions on the microstructure and melting temperatures of Al–Si–Cu filler metals

Abstract For the development of a low-melting-point filler metal for brazing aluminum alloys, a series of Al–Si–Cu–Zn alloys has been studied. Through differential thermal analysis (DTA) analysis, the melting temperatures of such Al–Si–Cu–Zn filler metals were determined. The results show that the addition of 10–30 wt.% copper into the traditional Al–12 wt.% Si filler metal causes its solidus temperature to decrease by about 60 °C. An addition of 10–30 wt.% zinc into such Al–Si–Cu ternary alloys will cause their solidus temperatures to drop further to a value lower than 500 °C. Metallographic observations indicate that the addition of zinc into the Al–Si–Cu alloys inhibits the formation of the Al–Si, Al–Cu and Al–Si–Cu eutectic phases. The remaining phases are a CuAl 2 intermetallic compound, an α-Al solid solution and silicon particles.

Morphology and growth kinetics of Ag3Sn during soldering reaction between liquid Sn and an Ag substrate

For the soldering of recycled Ag sputtering targets, the interfacial reaction between liquid Sn and an Ag substrate at temperatures ranging from 250 –425°C has been investigated. Experimental results show that a scallop-shaped layer of Ag3Sn intermetallic compounds formed during the soldering reaction. Kinetics analysis indicated that the growth of such interfacial Ag3Sn intermetallic compounds is diffusion-controlled with activation energy of 70.3kJ/mol. During the reaction, the Ag substrate dissolves into the molten Sn solder and causes the appearance of needle-shaped Ag3Sn precipitates in the Sn matrix.

Brazeability of a 3003 Aluminum alloy with Al-Si-Cu-based filler metals

Al-Si-Cu-based filler metals have been used successfully for brazing 6061 aluminum alloy as reported in the authors’ previous studies. For application in heat exchangers during manufacturing, the brazeability of 3003 aluminum alloy with these filler metals is herein further evaluated. Experimental results show that even at such a low temperature as 550 °C, the 3003 alloys can be brazed with the Al-Si-Cu fillers and display bonding strengths that are higher than 77 MPa as well. An optimized 3003 joint is attained in the brazements with the innovative Al-7Si-20Cu-2Sn-1Mg filler metal at 575 °C for 30 min, which reveals a bonding strength capping the 3003 Al matrix.

Brazeability of the 6061-T6 aluminum alloy with Al-Si-20Cu-based filler metals

The bond strength of the 6061-T6 aluminum alloy brazed with Al-12Si, Al-9.6Si-20Cu, and Al-7Si-20Cu-2Sn filer metals at a low temperature of 550°C is evaluated. The fractography of these brazements after tensile tests was observed using scanning electron microscopy (SEM). It was found that joints with good integrity can be produced with Al-7Si-20Cu-2Sn filler metal because it can be used in a temperature range of 504 to 526 °C, about 70 °C lower than the traditional Al-12Si filler metal. It was shown that joints of 6061-T6 aluminum alloy as the base metal, when brazed at 550 °C for 60 min using this new filler metal and ward, and after being subjected to a T6 treatment, possessed a high bonding strength of about 121 Mpa.

Interfacial reactions of liquid Sn and Sn-3.5Ag solders with Ag thick films

The interfacial reactions of liquid Sn and Sn-3.5Ag solders with Ag thick films are investigated in the temperature range from 250–325 °C, and the morphology of intermetallic compounds formed after such soldering reactions is observed. In kinetics analysis of the growths of intermetallic compounds, it was found that both Sn/Ag and Sn-3.5Ag/Ag reactions were interfacial-controlled, and the growth rates for both cases were similar. The rate of Ag dissolution into liquid solder attendant on the formation of interfacial intermetallic compounds after Sn/Ag reaction was about four times higher than that after Sn-3.5Ag/Ag reaction, as evidenced by experimental results.

Corrosion behavior of al–si–cu–(sn, zn) brazing filler metals

Abstract The corrosion behavior of Al–Si–Cu–(Sn, Zn) filler metals in a 3.5% NaCl aqueous solution were studied using electrochemical tests. The results showed that the addition of Sn or Zn to the Al–Si–Cu filler metal raised its corrosion current density sharply and caused its corrosion potential to become more active. Sn or Zn elements exert harmful effects on such low-melting-point brazing filler metals in that the corrosion resistance is degenerated, and damage is accelerated with an increase in the Sn or Zn content. Scanning electron microscopy (SEM) micrographs of the corroded surfaces of these Al–Si–Cu–(Sn, Zn) filler metals indicate that the Al-rich phase (i.e., Al–Si, Al–Si–Cu, and Al–Si–Cu–Sn eutectic phases) dissolves preferentially, while the Si particles and CuAl 2 ( θ ) intermetallic compounds remain intact.

Corrosion behaviors of Al-Si-Cu-based filler metals and 6061-T6 brazements

The corrosion behaviors of a series of Al-Si-Cu-based filler metals and the 6061-T6 butt joints brazed with these filler metals are evaluated by polarization tests and immersion tests in a 3.5% NaCl aqueous solution. For comparison, a traditional Al-12Si filler metal is also employed. The results indicate that the Al-Si-Cu-based filler metals before brazing possess much higher corrosion current densities and pitting tendencies than the Al-12Si filler metal. However, brazing of the 6061-T6 alloy with an Al-12Si filler metal produces a wider butt joint, which, in this case, creates a more extensive corrosion region. Severe galvanic corrosion occurs at the 6061-T6 joints when brazed with Al-Si-Cu-based filler metals. However, in the case of the 6061-T6/Al-12Si brazements, selective corrosion of the Al-12Si eutectic phase can be observed. The bonding strengths of the 6061-T6 butt joints brazed with various filler metals are also measured before and after the immersion tests.

Effects of microstructures on corrosion and stress corrosion behaviors of an Al-12.1 at.% Zn alloy

Various heat treatments of an Al-12.1 at.% Zn alloy would bring forth various types of microstructures such as solid solution (SS), continuous precipitation (CP), and discontinuous precipitation (DP), each of which contain respective shares of distribution of the aluminum-rich phases (α0, α) and the zinc-rich phase (β), and the corrosion behaviors of the said alloy may be affected as a result. Electrochemical measurements conducted in a 3 wt.% NaCl solution indicate that respective corrosion rates should be evinced in the following order: supersaturated SS<DP<CP. The difference in microstructures can also exert an influence on stress corrosion cracking (SCC) of the said alloy. Stress corrosion cracks propagate predominantly in an intercrystalline mode. However, the severe corrosion of precipitation sites may incur a change in crack propagation under applied stress. In that case, patches of transgranular fractures are found interspersed in the intergranular mode.