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2 2014

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Characterization of coatings on grey cast iron fabricated by hot-dipping in AlSi11 alloy

Mola R., Depczyński W.

Archives of Materials Science and Engineering

2014

Vol. 68, nr 1

20--23

Purpose: In this study, grey cast iron was aluminized by hot-dip coating with AlSi11 alloy. The microstructure and chemical composition of the coatings were analyzed to determine the effect of the bath temperature on the thickness of the coating. Design/methodology/approach: Flake graphite cast iron was aluminized by hot-dipping in AlSi11 alloy at 700°C or 750°C for 20 min. The microstructure and phase composition of the coatings were determined by means of an optical microscope and a scanning electron microscope with an EDS X-ray analyzer. Findings: It was found that the overall thickness of a coating was dependent on the temperature of the bath. The coatings consisted of an outer layer with the composition similar to the aluminizing bath and an inner intermetallic layer and dispersed graphite. The outer layer was much thicker for coatings fabricated at a temperature of 750°C. The thickness of the inner layer was similar for both bath temperatures. The inner layer was composed of two zones: the Al5Fe2 phase, adjacent to the cast iron substrate and the Al5FeSi phase, adjacent to the Al-Si outer layer. The interface between the layer of the Al5Fe2intermetallic phases and the substrate showed flat morphology. The Al5FeSi phase-outer layer interface was irregular. Practical limitations/implications: The results obtained through the investigations show that the temperature of the Al-Si bath has influence on the overall thickness of the coating. The thickness of the outer layer increases with an increase in the bath temperature. The thickness of the inner layer, however, is not affected by the bath temperature. Originality/value: Coatings produced by hot-dipping in pure aluminium are characterized by a microstructure with a relatively thick inner layer of intermetallic phases.

Characterization of Coatings on Grey Cast Iron Fabricated by Hot-dipping in Pure Al, AlSi11 and AlTi5 Alloys

Mola R., Bucki T., Wcisło K.

Archives of Foundry Engineering

2014

Vol. 14, iss. 1

85--90

Flake graphite cast iron was hot-dip coated with pure aluminium or aluminium alloys (AlSi11 and AlTi5). The study aimed at determining the influence of bath composition on the thickness, microstructure and phase composition of the coatings. The analysis was conducted by means of an optical microscope and a scanning electron microscope with an EDS spectrometer. It was found that the overall thickness of a coating was greatly dependent on the chemical composition of a bath. The coatings consisted of an outer layer and an inner intermetallic layer, the latter with two zones and dispersed graphite. In all the cases considered, the zone in the inner intermetallic layer adjacent to the cast iron substrate contained the Al5Fe2 phase with small amount of silicon; the interface between this phase and the cast iron substrate differed substantially, depending on the bath composition. In the coatings produced by hot-dipping in pure aluminium the zone adjacent to the outer layer had a composition similar to that produced from an AlTi5 bath, the Al3Fe phase was identified in this zone. The Al3Fe also contained silicon but its amount was lower than that in the Al5Fe2. In the coatings produced by hot-dipping in AlSi11, the zone adjacent to the outer layer contained the Al3FeSi phase. The analysis results showed that when AlSi11 alloy was applied, the growth mode of the inner layer changed from inwards to outwards. The interface between the Al5Fe2 phase and the cast iron substrate was flat and the zone of this phase was very thin. Locally, there were deep penetrations of the Al5FeSi phase into the outer layer, and the interface between this phase and the outer layer was irregular. Immersion in an AlTi5 bath caused that the inner intermetallic layer was thicker than when pure aluminium or AlSi11 alloy baths were used; also, some porosity was observed in this layer; and finally, the interface between the inner layer and the cast iron substrate was the most irregular.