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Coatings 2017, 7(12), 222; doi:10.3390/coatings7120222

Identification of Intermetallic Compounds and Its Formation Mechanism in Boron Steel Hot-Dipped in Al-7 wt.% Mn Alloy

1
Department of Material Science and Engineering, Pusan National University, Busan 46241, Korea
2
Department of Hybrid Materials & Machining Technology, Graduate School of Convergence Science, Pusan National University, Busan 46241, Korea
*
Author to whom correspondence should be addressed.
Academic Editor: Joaquim Carneiro
Received: 10 November 2017 / Revised: 27 November 2017 / Accepted: 1 December 2017 / Published: 6 December 2017
(This article belongs to the Special Issue Hybrid Surface Coatings & Process (Selected Papers from HyMaP 2017))
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Abstract

In laser welding and hot stamping Al-Si-coated boron steel, there is a problem that the strength of the joint is lowered due to ferrite formation in the fusion zone. The purpose of this study is to develop an Al-7 wt.% Mn hot-dip coating in which Mn, an austenite stabilizing element, replaces the ferrite stabilizing element Si. The nucleation and formation mechanism of the reaction layer was studied in detail by varying the dipping time between 0 and 120 s at 773 °C. The microstructure and phase constitution of the reaction layer were investigated by various observational methods. Phase formation is discussed using a phase diagram calculated by Thermo-CalcTM. Under a 30 s hot-dipping process, no reaction occurred due to the formation of a Fe3O4 layer on the steel surface. The Fe3O4 layer decomposed by a reduction reaction with Al-Mn molten alloy, constituent elements of steel dissolved into a liquid, and the reaction-layer nucleus was formed toward the liquid phase. A coated layer consists of a solidified layer of Al and Al6Mn and a reactive layer formed beneath it. The reaction layer is formed mainly by inter-diffusion of Al and Fe in the solid state, which is arranged on the steel in the order of Al11Mn4 → FeAl3 (θ) → Fe2Al5 (η) phases, and the Fe3AlC (κ) in several nm bands formed at the interface between the η-phase and steel. View Full-Text
Keywords: hot-dipped coating; Fe–Al–Mn phases; nucleation and growth; phase transformation; diffusion; advanced high-strength steel hot-dipped coating; Fe–Al–Mn phases; nucleation and growth; phase transformation; diffusion; advanced high-strength steel
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Kwak, S.-Y.; Yun, J.-G.; Lee, J.-H.; Shin, D.-I.; Kang, C.-Y. Identification of Intermetallic Compounds and Its Formation Mechanism in Boron Steel Hot-Dipped in Al-7 wt.% Mn Alloy. Coatings 2017, 7, 222.

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