The Effect of Ductile Cast Iron Matrix on Zinc Coating During Hot Dip Galvanising of Castings

Abstract

The growth kinetics of the zinc coating formed on the surface of casting made from ductile iron grade EN-GJS-500-3 was investigated. To produce homogenous metal matrix in test samples, the normalising and ferritising annealing was carried out. Studies showed a heterogeneous structure of cast iron with varying content of the phases formed. This was followed by hot dip galvanising treatment at 450°C to capture the growth kinetics of the zinc coating (the time of the treatment ranged from 60 to 600 seconds). Nonlinear estimation of the determined growth kinetics of the alloyed layer of a zinc coating was made and an equation of the zinc coating growth was derived. Based on the results of the investigations it was concluded that thickness of the zinc coating formed on the surface of casting with a 100% pearlitic matrix makes 55% of the thickness of coating formed on the surface in 100% ferritic.

Shaping optimal zinc coating on the surface of high-quality ductile iron casting. Part I – Moulding technologies vs. zinc coating

“…The cast iron chemical composition and various grades used in the tests are compared in Table 1. Castings were made in the form of plates and from those plates the test samples were cut out [12]. Chemical treatment of the casting surface as well as cleaning and hot-dip galvanizing were carried out in a conventional manner [13].…”

Growth Law For Peritectic Phases Formation In The Zinc Coating

“…The δ -phase is again the dominant phase in the coating at time t = 300 s. At this time, the first solid / solid transformation begin to occur. Then, the sublayer of the δ -phase grow at the expense of the ζ -phase sub-layer, [1][2][3][4][5][6][7][8][9][10][11][12][13]. Qualitative analysis of the sequence of the coating formation allows estimating the time, t M as equal to 300 seconds.…”

“…The known analyses have proved that the coatings obtained from the hot-dip galvanizing are composed of two main layers, [1][2][3][4][5][6][7][8][9][10][11][12][13]. The first layer, directly contacting the substrate, is an alloyed layer usually composed of a few sub-layers of the intermetallic phases/compounds.…”

“…The first layer, directly contacting the substrate, is an alloyed layer usually composed of a few sub-layers of the intermetallic phases/compounds. The external layer, solidifying on the surface of the alloyed layer, is formed when the galvanized product is emerged from the bath, [10][11][12][13][14][15].…”

Flux Effect Onto Peritectic Phases Growth In The Zinc Coating

“…As the (Zn) -coating consists of two layers: first layer being directly in the contact with substrate and second layer being the result of the substrate/ coating system emerging from the zinc bath, the adhesion between substrate and first layer is of the main significance for the technology, [12][13][14][15].…”