New evidence for the formation and growth mechanism of the intermetallic phase formed at the Al/Fe interface
- PDF / 586,543 Bytes
- 9 Pages / 584.957 x 782.986 pts Page_size
- 1 Downloads / 195 Views
To clarify the underlying mechanism of formation and growth of aluminum coating, the interface microstructures of as-prepared aluminum coating iron were investigated using various experimental methods. The liquid Al–Si, Al–Ge alloys were chosen as the dipping baths. In both cases, the total thickness of the reaction layer is controlled mainly by the well-known diffusion growth of g-Al5Fe2. The melt environment of the Al bath plays a decisive role in the formation and growth of the diffusion layer. The results show that Ge atoms could also decelerate reaction layer growth like Si atoms, which mainly restrain the diffusion of Al atoms. Meanwhile, Ge element represents an abnormal concentration gradient in the g-Al5Fe2 phase. The diverse growth behavior of the diffusion layer is attributed to the strong controlling role of the alloying element in Al baths based on the atomic diffusion and activity analysis.
I. INTRODUCTION
Aluminum (Al) and iron (Fe) are two most abundant metals in the earth’s crust and have been widely used in various applications due to their excellent physical and chemical properties. The dissimilar metal joints between Al and Fe present potential prospects because such joints provide a perfect combination of a higher strengthto-weight ratio, an extraordinary corrosion resistance and an excellent thermal conductivity.1 A precondition for realizing perfect aluminum coating of iron (or steel) is to obtain an effective bonding between aluminum alloys and iron at the initial stage of hot dipping. The metallurgical diffusion layer between Al and Fe has been proved to play a fundamental role in material properties during the process of manufacture and assembling. However, it is generally believed that interfaces are weaker in comparison to matrix in terms of shearing and bending, since atoms within interfaces usually have low coordination bonds2 and brittle intermetallic phases are commonly formed at the interfaces.3,4 During the solidification of Al/Fe joints, owing to the differences in the thermal expansion coefficients among Al substrate, intermetallic phases, and Fe substrate, a mass of microcracks appear in the intermetallic phases, which are detrimental to the mechanical properties of Al/Fe joints formed in welding and coating procedures.5,6 Apparently, it is essential to investigate the formation and growth mechanism of intermetallic phases between solid Fe and liquid Al alloys. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.345 J. Mater. Res., Vol. 28, No. 23, Dec 14, 2013
http://journals.cambridge.org
Downloaded: 11 Mar 2015
Previous works have confirmed the role of Al5Fe2 phase (dominant reaction product) at the interface between solid Fe and liquid Al and the existence of a thin layer of Al13Fe4 phase.7–10 Although the addition of Si into Al has been reported to make a difference in decelerating the reaction layer’s growth during solid Fe/liquid Al–Si interdiffusion experiments and the nearly flat growth front has been observed at the reaction la
Data Loading...
