Microstructure and formability of ZnNi alloy electrodeposited sheet steel

Abstract

ZnNi alloy electrodeposited sheet steels were made from a chloride bath using a high-speed flow cell. A Ni-rich flash coating was deposited first, upon which the ZnNi coating, with Ni contents ranging from 8 to 16 wt pct, was subsequently electrodeposited. It is demonstrated that the Ni content of the coating affects the forming properties and microstructure of the ZnNi coatings. The hardness of the ZnNi coating increased with Ni content, leading to poor formability and inferior adhesion of the coated steels, as evident from the large amount of coating loss during swift cupping and coating peel-off during low-temperature adhesion tests. On the other hand, the friction force between the coated steel and cupping die decreased with increasing Ni content. At low Ni contents of 8 wt pct, the coating had a porous equiaxed grain structure. As the Ni content increased, the coating surface changed to dense faceted morphologies. A pyramid morphology was observed for 16 wt pct ZnNi coatings. An X-ray diffraction (XRD) analysis showed that all coatings containing up to 16 wt pct Ni contained only ␥ phase. Transmission electron microscopy (TEM) observations showed the 8 wt pct Ni coating to have a fine-grained structure, which changed to a columnar structure at 16 wt pct Ni. The formation of the columnar structure is explained by the smaller amount of hydrogen discharge as the bath Ni ion concentration increased.

Texture and surface morphology in zinc electrodeposits

“…The coating properties such as corrosion resistance, paintability and formability are closely related to the morphology and texture of the coating [1-7, Raeissi et al, submitted for publication]. Various morphologies and textures may develop by changing electrochemical deposition parameters such as current density, temperature, pH, substrate surface preparation and bath composition [7][8][9][10][11][12][13]. Although there has been work on the effect of electrochemical variables on the texture of zinc electrodeposits [7-13, Raeissi et al, submitted for publication], texture development and the reasons for its variation with changes of electrochemical parameters are not completely clear.…”

The properties and the effect of operating parameters on nickel plating (review)

“…The dimple rupture with small micro voids has been observed after the fracture of specimen. Lin et al (2000) investigated microstructure and formability of ZnNi alloy electrodeposited sheet steel. ZnNi alloy electrodeposited sheet steels were made from a chloride bath using a high-speed flow cell.…”

Prediction of Damage to the Vehicle Underbody due to Stone Chipping

“…The stone chipping problem can be passively solved by applying electroplating and ceramic coating for protecting the large body chassis against external impact [3]. However, it is difficult to design the external parts of a vehicle and set the safety factor for the parts exposed to the external environment.…”