Crystallographic Characterization of an Electroplated Zinc Coating Prone to Whiskers

A Zn-electroplated steel prone to Zn whiskers has been investigated in order to obtain information about the microstructure of the Zn coating at the root of a whisker. Indeed, the characterization of the Zn coating is essential to understand the Zn whisker growth mechanism. Care was taken to prepare a sample at a whisker root by using a focused-ion beam in a dual-beam scanning electron microscope. The sample was analyzed using energy dispersive X-ray spectrometry and electron backscattered diffraction. Results show three different regions: 1) an inclusion enriched with Ca, Al, and C; 2) the Zn coating with columnar grains; and 3) the root of the whisker. An important point is that recrystallized grains are found at the whisker root. This observation supports recent whisker growth models based on recrystallization.