High temperature deformation behaviors of hot dip 55 wt% Al-Zn coated steel

Abstract

The high temperature tensile test of hot dip 55 wt% Al-Zn coated steel was performed to study the fracture behaviors of hot dip 55 wt% Al-Zn coating as a protective coating for hot-stamping steel. During austenitization, the 55 wt% Al-Zn coating had transformed to an alloy layer composed an Fe2Al5Znx (with few FeAl and Zn) outer layer and an FeAl inner layer. When the austenitization heat treatment was fixed at 5 min, the sample heated at a higher heating rate (20 K/s) was subjected to a longer soaking time at 900 °C. This resulted in a thicker FeAl inner layer at the steel/Fe2Al5Znx (FeAl, Zn) interface. During the initial stages of deformation, cracks formed in Fe2Al5Znx (FeAl, Zn) layer. Subsequently, cracks developed in the FeAl inner layer. With continued deformation, cracks widened and debonding occurred at the FeAl/Fe2Al5Znx (FeAl, Zn) interface for the samples heated at lower heating rates (5 K/s or 10/s). Finally, crack widening accelerated the exposure and subsequent oxidation of the steel substrate. The absence of debonding can be beneficial for reducing the susceptibility to powdering during hot stamping.