Changes

The manufacturing of strips and wires by internal oxidation starts with a molten alloy of silver and cadmium. During a heat treatment below it's melting point in a oxygen rich atmosphere in such a homogeneous alloy the oxygen diffuses from the surface into the bulk of the material and oxidizes the Cd to CdO in a more or less fine particle precipitation inside the Ag matrix. The CdO particles are rather fine in the surface area and are becoming larger further away towards the center of the material <xr id="fig:fig2.83Micro structure of AgCdO9010"/> (Fig. 2.83).

During the manufacturing of Ag/CdO contact material by internal oxidation the processes vary depending on the type of semi-finished material. For Ag/CdO wires a complete oxidation of the AgCd wire is performed, followed by wire-drawing to the required diameter <xr id="fig:Strain hardening of internally oxidized AgCdO9010"/> (Figs. 2.77) and <xr id="fig:Softening of internally oxidized AgCdO9010"/> (Fig. 2.78). The resulting material is used for example in the production of contact rivets. For Ag/CdO strip materials two processes are commonly used: Cladding of an AgCd alloy strip with fine silver followed by complete oxidation results in a strip material with a small depletion area in the center of it's thickness and a Ag backing suitable for easy attachment by brazing (sometimes called “Conventional Ag/CdO”). Using a technology that allows the partial oxidation of a dual-strip AgCd alloy material in a higher pressure pure oxygen atmosphere yields a composite Ag/CdO strip material that has besides a relatively fine CdO precipitation also a easily brazable AgCd alloy backing <xr id="fig:fig2.85Micro structure of AgCdO9010ZH"/> (Fig. 2.85). These materials (DODURIT CdO ZH) are mainly used as the basis for contact profiles and contact tips.

During powder metallurgical production the powder mixed made by different processes are typically converted by pressing, sintering and extrusion to wires and strips. The high degree of deformation during hot extrusion produces a uniform and fine dispersion of CdO particles in the Ag matrix while at the same time achieving a high density which is advantageous for good contact properties <xr id="fig:fig2.84Micro structure of AgCdO9010P"/> (Fig. 2.84). To obtain a backing suitable for brazing, a fine silver layer is applied by either com-pound extrusion or hot cladding prior to or right after the extrusion <xr id="fig:fig2.86Micro structure of AgCdO8812WP"/> (Fig. 2.86).

<xr id="fig:fig2.80Softening of AgCdO9010P after annealing"/> Fig. 2.80: Softening of Ag/CdO 90/10 P after annealing for 1 hr after 40% cold working

<xr id="fig:fig2.81Strain hardening of AgCdO8812"/> Fig. 2.81: Strain hardening of Ag/CdO 88/12 WP

<xr id="fig:fig2.82Softening of AgCdO8812WP after annealing"/> Fig. 2.82: Softening of Ag/CdO 88/12WP after annealing for 1 hr after different degrees of cold working

<xr id="fig:fig2.83Micro structure of AgCdO9010"/> Fig. 2.83: Micro structure of Ag/CdO 90/10 i.o. a) close to surface b) in center area

<xr id="fig:fig2.84Micro structure of AgCdO9010P"/> Fig. 2.84: Micro structure of Ag/CdO 90/10 P: a) perpendicular to extrusion direction b) parallel to extrusion direction

<xr id="fig:fig2.85Micro structure of AgCdO9010ZH"/> Fig. 2.85: Micro structure of Ag/CdO 90/10 ZH: 1) Ag/CdO layer 2) AgCd backing layer

<xr id="fig:fig2.86Micro structure of AgCdO8812WP"/> Fig. 2.86: Micro structure of AgCdO 88/12 WP: a) perpendicular to extrusion direction b) parallel to extrusion direction

<figure id="fig:fig2.80Softening of AgCdO9010P after annealing">

<figure id="fig:fig2.81Strain hardening of AgCdO8812">

<figure id="fig:fig2.82Softening of AgCdO8812WP after annealing">

<figure id="fig:fig2.83Micro structure of AgCdO9010">

<figure id="fig:fig2.84Micro structure of AgCdO9010P">

<figure id="fig:fig2.85Micro structure of AgCdO9010ZH">

<figure id="fig:fig2.86Micro structure of AgCdO8812WP">