Heat Testing

A common question about products that are manufactured with electroplated metal parts is: How are metal coatings tested? Included in the many metal coating quality control checks is an electroplating test for adhesion. One of the more reliable and commonly applied adhesion testing processes is a method known as a heat-quench test.

How Is Heat Used to Test for Adhesion?

As the name implies, a heat-quench test relies on subjecting electroplated parts to elevated temperatures to determine the sufficiency of coating adhesiveness. The process entails placing the parts into an oven and heating them until they reach the appropriate temperature, which varies depending on the type and chemical composition of the metal. Special accommodations should be made for metal coatings that are susceptible to oxidation, such as heating them in an inert environment or suitable liquid.

Once the heating process is complete, the parts are then “quenched” by dousing them with water or another suitable room-temperature liquid. The appearance of flaking or peeling after quenching is a sign of insufficient adhesion. Blistering may also occur during heating or quenching as the result of the plating liquid becoming trapped in pits or pores on the substrate surface. However, this is not necessarily a sign of improper adhesion.

Which Metal Coatings Are Best Suited for Heating Testing for Adhesion?

The heat-quench test is most effective when used on parts with the following metal coatings:

• Chromium
• Copper
• Lead
• Nickel
• Nick/Chromium
• Silver
• Tin
• Gold

This process is not recommended for use with cadmium, rhodium, palladium or zinc coatings.

Oven temperature is a key factor that will affect the reliability of the heat-quench test outcome. The appropriate temperature can vary widely depending on the substrate and coating combination. For instance, a steel substrate with a tin coating should be heated to 150° C, while an aluminum base with a gold or silver coating should be heated to 220° C. It is also important to maintain the temperature within 10° C of the desired level throughout the heating process.

Is the Heat-Quench Test Safe for Metal Parts?

The heat-quench test will not have any harmful effects on finished parts, as long as the appropriate oven temperature is maintained for the duration of the process. In some cases, a brittle top layer may form during heating that may result in peeling. However, this is an indication of fracturing of the newly formed layer as opposed to poor adhesion.