The Effect of Electroplated Copper and Zinc Coatings on Friction Conditions

Abstract

The paper presents the results of investigation of dry friction coefficient for a pin-on-disk couple. The pin was made of steel while the steel disk was electrochemically coated with a 20 μm copper or zinc layer. The pins and disks were ground and subsequently matched to have the same roughness grade. The roughness grade of the disks was 9 before coating whereas after coating it was 9 for copper and 10 for zinc. On the basis of the analysis of the friction surface it was found that copper is characterized by adhesive wear while abrasive wear is characteristic of zinc. The wear after 3600 s of friction (equal to 360 m of distance covered) was of the order of 20 μm. Friction led to transfer of the electroplated metal from the disk onto the steel pin. This process was more intensive for copper than for zinc whereas transfer of iron from the pin onto the disk was considerably less intensive.
Tribological measurements were carried out using T-01M tester. Coefficient of friction as a function of time from 0 to 3600 s (distance covered – 360 m) was determined for three unit pressures: 0.4 MPa, 0.8 MPa and 1.2 MPa. For zinc the μ values ranged from 0.4 to 0.5 and did not depend strongly on time and loads. For copper the coefficient of friction (about 0.2) did not depend on load during the first 120 s; whereas its final values were different at different pressures: 0.63 at 0.4 MPa, 0.75 at 0.8 MPa and 0.8 at 1.2 MPa.