Phase Composition of Al-Si Coating from the Initial State to the Hot-Stamped Condition.

Vojtech Kucera,Dalibor Vojtech,Jaroslav Petr-Soini,Marcello Cabibbo,Tomas Pilvousek,Jaroslav Fojt,Filip Prusa,Marie Kolarikova

doi:10.3390/ma14051125

Abstract

The chemical and phase composition of the coating and the coating/substrate interface of an Al-Si-coated 22MnB5 hot stamped steel was investigated by means of SEM-EDS, XRD, micro-XRD and electron diffraction. Moreover, the surface profile was analyzed by XPS and roughness measurements. The XPS measurements showed that the thickness of the Si and Al oxide layers increased from 14 to 76 nm after die-quenching, and that the surface roughness increased as well as a result of volume changes caused by phase transformations. In addition to the FeAl(Si) and Fe2Al5 phases and the interdiffusion layer forming complex structures in the coating, electron diffraction confirmed the presence of an Fe2Al5 phase, and also revealed very thin layers of Fe3(Al,Si)C, Fe2(Al,Si)5 and Al-bearing rod-shaped particles in the immediate vicinity of the steel interface. Moreover, the scattered nonuniform layer of the Fe2Al8Si phase was identified in the outermost layer of the coating. Despite numerous studies devoted to researching the phase composition of the Al-Si coating applied to hot stamped steel, electron diffraction revealed very thin layers and particles on the coating/substrate interface and outermost layer, which have not been analyzed in detail.

Highlights

With incessantly increasing pressure on the automotive industry, manufacturers are being forced to develop new technologies and materials to reduce car body weight
The Al-Si coating was commercially produced by continuous immersion in a bath with an approximate chemical composition of 90 wt.% Al and 10 wt.% Si
The hot-dipped Al-Si coating was first investigated as the initial state for austenitization and die-quenching by means of Scanning electron microscope (SEM)-EDS, XRD and micro-XRD

Summary

Introduction

With incessantly increasing pressure on the automotive industry, manufacturers are being forced to develop new technologies and materials to reduce car body weight. This can be achieved by hot stamping technology capable of producing press-hardened steel (PHS), reaching an ultimate tensile strength of up to 2000 MPa. Hot stamping significantly suppresses the spring-back effect compared to conventional cold press forming, and ensures the geometric accuracy of pressed parts. PHS is used mostly to produce safety components such as A-pillars, B-pillars, bumpers, roof rails, rocker rails and tunnels. PHS enhances the toughness of the vehicle frame and passenger safety. Its proportional content in car bodies attracts increasing attention [1,2,3]

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