Baohong Tian

Cyanide-free silver electroplating process in thiosulfate bath and microstructure analysis of Ag coatings

Abstract Cyanide-free silver electroplating was conducted in thiosulfate baths containing AgNO 3 and AgBr major salts, respectively. The effects of major salt content and current density on surface quality, deposition rate and microhardness of Ag coatings were investigated. The optimized electroplating parameters were established. The adhesion strength of Ag coating on Cu substrate was evaluated and the grain size of Ag coating was measured under optimized electroplating parameters. The optimized AgNO 3 content is 40 g/L with current density of 0.25 A/dm 2 . The deposited bright, smooth, and well adhered Ag coating had nanocrystalline grains with mean size of 35 nm. The optimized AgBr content was 30 g/L with current density of 0.20 A/dm 2 . The resultant Ag coating had nanocrystalline grains with mean size of 55 nm. Compared with the bath containing AgBr main salt, the bath containing AgNO 3 main salt had a wider current density range, and corresponding Ag coating had a higher microhardness and a smaller grain size.

Hot deformation behavior and processing map of Cu–Ni–Si–P alloy

Abstract The high-temperature deformation behavior of Cu–Ni–Si–P alloy was investigated by using the hot compression test in the temperature range of 600-800 °C and strain rate of 0.01–5 s −1 . The hot deformation activation energy, Q , was calculated and the hot compression constitutive equation was established. The processing maps of the alloy were constructed based on the experiment data and the forging process parameters were then optimized based on the generated maps for forging process determination. The flow behavior and the microstructural mechanism of the alloy were studied. The flow stress of the Cu–Ni–Si–P alloy increases with increasing strain rate and decreasing deformation temperature, and the dynamic recrystallization temperature of alloy is around 700 °C. The hot deformation activation energy for dynamic recrystallization is determined as 485.6 kJ/mol. The processing maps for the alloy obtained at strains of 0.3 and 0.5 were used to predict the instability regimes occurring at the strain rate more than 1 s −1 and low temperature (≤650 °C). The optimum range for the alloy hot deformation processing in the safe domain obtained from the processing map is 750–800 °C at the strain rate of 0.01–0.1 s −1 . The characteristic microstructures predicted from the processing map agree well with the results of microstructural observations.

Electrotribological behavior of Cu−Ag−Zr contact wire against copper-base strip

Cu−Ag−Zr alloy has an excellent combination of mechanical strength and electrical conductivity, and is a promising contact wire material for high-speed electrified railways. An investigation of the electritrobological behavior of Cu−Ag−Zr wire is presented here. Wear tests are conducted under laboratory conditions with a specified sliding wear tester that simulated train motion under an electrical current applied across the sliding interface. The Cu−Ag−Zr alloy wire is slid against a copper-based powder metallurgy strip used in railway systems under unlubricated conditions. Worn surfaces of the Cu−Ag−Zr alloy wire are analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrum (EDS). Within the studied range of electrical current, normal pressure, and sliding speed, the wear rate increases with increasing electrical current and sliding distance. Adhesive wear, abrasive wear, and electrical erosion are the dominant mechanisms during the electrical sliding processes. Compared with a Cu−Ag contact wire under the same test conditions, the Cu−Ag−Zr alloy wire has much better wear resistance.

Hot Deformation and Dynamic Recrystallization Behavior of the Cu-Cr-Zr-Y Alloy

To study the workability and to optimize the hot deformation processing parameters of the Cu-Cr-Zr-Y alloy, the strain hardening effect and dynamic softening behavior of the Cu-Cr-Zr-Y alloy were investigated. The flow stress increases with the strain rate and stress decreases with deformation temperature. The critical conditions, including the critical strain and stress for the occurrence of dynamic recrystallization, were determined based on the alloy strain hardening rate. The critical stress related to the onset of dynamic recrystallization decreases with temperature. The evolution of DRX microstructure strongly depends on the deformation temperature and the strain rate. Dynamic recrystallization appears at high temperatures and low strain rates. The addition of Y can refine the grain and effectively accelerate dynamic recrystallization. Dislocation generation and multiplication are the main hot deformation mechanisms for the alloy. The deformation temperature increase and the strain rate decrease can promote dynamic recrystallization of the alloy.

Electrotribological property of the Cu−Ag−Cr alloy with high-strength and high-conductivity

By means of a vacuum induction furnace, a Cu−Ag−Cr alloy was produced. The electrotribological property and mechanism of the Cu−Ag−Cr alloy wear studied via wear property tests, scanning electron microscope (SEM), energy dispersive X-ray spectrum (EDS) and transmission electron microscopy (TEM). Wear tests were conducted with a specially designed sliding wear tester, which simulated the tribological conditions of sliding current collectors on contact wires in a railway system. The alloy wire was slid against a copperbased powder metallurgy strip under non-lubricated conditions. The results showed that the wear rate of Cu−Ag−Cr alloy increases as the sliding speed increases under a normal load. Adhesive wear, abrasive wear, and electrical erosion wear are the governing wear mechanisms under the electrical current sliding processes. Under the same conditions, the wear resistance of the Cu−Ag−Cr alloy is 2–3 times that of the Cu−Ag alloy.

Internal stress analysis of electroplated films based on electron theory

Abstract Cu films on Fe, Ni and Ag substrates, Ni films on Fe and Ag substrates, Ag film on Cu substrate, Cr film on Fe substrate, Ag film on Ag substrate, Ni film on Ni substrate and Cu film on Cu substrate were deposited by electroplating. The average internal stress in all films, except Cr, was in-situ measured by the cantilever beam test. The interfacial stress is very large in the films with different materials with substrates and is zero in the films with the same material with substrates. The interfacial stress character obtained from the cantilever beam bending direction is consistent with that obtained from the modified Thomas-Fermi-Dirac electron theory.

Study on thermal deformation behavior of Cu-Zr-Ce alloy

The flow stress curves of Cu-1.0%Zr-0.15%Ce alloy during high temperature deformation were analyzed by using a Gleeble-1500D thermal simulation machine at the hot deformation temperature of 550 C, 650 C, 750 C, 850 C and 900 C, the strain rate of 0.001 s -1 、 0.01 s -1 、0.1 s -1 、1 s -1 、10 s -1 , respectively. The results show that the hot deformation mechanism of the alloy is mainly based on the dynamic recovery under relative lower hot deformation temperature or higher strain rate. The thermal deformation mechanism of the Cu-1.0%Zr-0.15%Ce alloy is the dynamic recrystallization under relative higher hot deformation temperature or lower strain rate. The constitutive equation of the alloy was calculated and established respectively on the basis of the relationships among the flow stress, strain rates and deformation temperature. The thermal activation energy of the alloy is about 430.51 kJ/mol.

Influence of neodymium on microstructure and mechanical properties of AZ31B wrought magnesium alloy

Abstract The influences of rare earth neodymium on microstructure and mechanical properties of as cast and hot rolled AZ31B wrought magnesium alloy were investigated. The results show that the mechanical properties of both as cast and hot rolled AZ31B alloys decrease due to Nd addition. Nd reacts with Al to form Al2Nd phase when Nd is added. Bulky and brittle Al2Nd intermetallic degrades the mechanical properties. Moreover, the addition of Nd weakens the grain refining effect of Al on as cast AZ31B alloy, resulting in grain coarsening. Coarse grains also cause the decline of the mechanical properties of as cast AZ31B–Nd alloy. The negative influence of the bulky and brittle intermetallics on mechanical properties of AZ31B alloy can be relieved by large deformation because the intermetallics can be sufficiently broken up during the deformation process.