Title: Electrospark deposition of ZrB2-TiB2 composite coating on Cu-Cr-Zr alloy electrodes

Authors: Ping Luo; Shijie Dong; Anzhuo Yangli; Shixuan Sun; Zhong Zheng

Addresses: College of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China ' Hubei Provincial Key Laboratory of Green Materials for Light Industry, Hubei University of Technology, Wuhan, 430068, China ' Hubei Provincial Key Laboratory of Green Materials for Light Industry, Hubei University of Technology, Wuhan, 430068, China ' Capital Aerospace Machinery Corporation, Beijing 100076, China ' Hubei Provincial Key Laboratory of Green Materials for Light Industry, Hubei University of Technology, Wuhan, 430068, China

Abstract: To improve electrode life during the resistance spot welding of aluminium alloy sheets, a ZrB2-TiB2 composite coating was synthesised on the surfaces of spot-welding electrodes through an electrospark deposition process. The microstructure, elemental composition, phase structure, and mechanical properties of the coating were characterised using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and microhardness testing. It was found that extensive cracking occurred in the monolithic ZrB2-TiB2 coating and at the coating-electrode interface. When the ZrB2-TiB2 coating was deposited on electrodes precoated with Ni, the number of defects decreased significantly. Further, delamination did not occur, fewer cracks were formed, and metallurgical bonds formed at the interface. The average hardness of the multilayered ZrB2-TiB2/Ni coating was approximately HV 1050 and lower than that of the monolithic ZrB2-TiB2 coating (HV 1280). For all the investigated coating conditions, a narrow, softened zone was observed near the coating-substrate interface. The softening mechanism was different for the two cases. In the case of the monolithic ZrB2-TiB2 coating, a heat-affected zone (HAZ) with large crystallites was formed. In the case of the multilayer ZrB2-TiB2/Ni coating, the zone was formed owing to the metallurgical reaction of Ni with the substrate as well as the mixing of Ni with the substrate.

Keywords: electrospark deposition; ESD; copper alloy electrodes; zirconium diboride; titanium diboride; ZrB2; TiB2; composite coatings; electrode life; resistance spot welding; aluminium alloy sheets; aluminium alloys; microstructure; phase structure; mechanical properties; microhardness; cracking; coating-substrate interface; nickel precoating.

DOI: 10.1504/IJSURFSE.2016.075316

International Journal of Surface Science and Engineering, 2016 Vol.10 No.1, pp.41 - 54

Received: 23 Oct 2014
Accepted: 24 Nov 2014

Published online: 11 Mar 2016 *

Full-text access for editors Access for subscribers Purchase this article Comment on this article