Luhai Wu

Welding by Metal-Electrolyte Discharge

A new welding method by using metal-electrolyte discharge has been demonstrated. This method that needs only a common 220 V power supply and a common salt solution, can be used to weld metal wires and foils. At 220 V, the successfully welded maximal wire diameter is 2 mm, 1.5 mm, and 0.3 mm for Al, Fe, and Cu, respectively, in a saturated KCl solution at room temperature. At the same conditions the successfully welded maximal foil thickness is 1 mm, 0.4 mm, and 0.2 mm for Al, Fe, and Cu, respectively. The higher voltage and higher electrolyte concentration imply higher welding ability. With further comprehensive investigation and the processing modification, this method may be developed as a simple and low-cost in situ welding method especially for metal wire connection.

Diffusion bonding of mismatch dental alloys.

The diffusion bonding of Ti-6Al-4V and Co-Cr-Mo dental alloys has been investigated in terms of the atoms diffusion, the microstructure evolution, and the bonding strength. The bonding performance reveals asymmetry diffusion profiles for both the Co and Cr in Ti-6Al-4V and the Ti in Co-Cr-Mo alloy. Their diffusion coefficients (Arrhenius relations) have been established based on the experiments. Co and Cr diffusion into Ti-6Al-4V leads to alpha --> beta transformation and the intermetallics-formation. Maximum bonding strength occurs at about 840 degrees C. The bonding joint fails under the shear stress in the Ti-6Al-4V side near the bonding interface in brittle manner. The intermetallics in the diffusion layer together with the unbonded areas and other flaws in the bonding interface are responsible for the shear brittle fracture, which also weaken the bonding strength.