For connectors of electronic components installed in automobiles, Sn plating is used as surface treatment. Demand is increasing recently for reduction of connector insertion force and for improvement of connection reliability in high-temperature environments. To meet those demands, various processes using Sn-based intermetallic compounds have been developed as alternative surface treatments for Sn plating. Needs for automotive connectors are expected to continue their expansion. Therefore, we investigated a Sn-Cu plating process able to provide more stable characteristics. After stacking Sn-Cu plating and Sn plating, thermal treatment was used to form intermetallic compounds. Just below the surface, Cu6 Sn5 intermetallic compound layers with low roughness are formed. A pure Sn layer is then formed on it. Forming a pure Sn layer with high connection reliability and an intermetallic compound layer with high hardness in a stable state can be expected to improve various characteristics. Evaluation of the friction coefficients and the contact resistance obtained using the investigated process revealed that good characteristics were obtained.
To improve red rust resistance at the initial stage of corrosion in exposed steel parts of Zn-11 mass%Al-3 mass%Mg-0.2 mass%Si coated steel sheets, we investigated the mechanism and effects of applying a chemical conversion coating including a corrosion inhibitor to the zinc alloy coating.
A pure-water-spray cyclic corrosion test revealed effects of combining a zinc alloy coating and chemical conversion coating. Red rust resistance in the exposed part of the steel substrate at the initial stage of corrosion is improved by application of a phosphoric-acid-containing chemical conversion coating. When the phosphoric-acid-containing chemical conversion coating was applied, Mg, Zn, and P of the coating components moved farther from the coating layer - steel substrate interface. Because the Mg2＋, Zn2＋, PO43−, CO32−, and OH− compound protected the steel substrate, the steel substrate corrosion was suppressed even when the water film became thin or island-shaped and when the sacrificial anticorrosive action of the coating worked only with difficulty.
As the electrical conductivity of the water film increased, the increase in the sacrificial protection distance to the steel substrate by the coating component probably also contributed to suppression of the steel substrate corrosion when the water film became thick.