Growth mode of interfacial products of Csf/Mg-7.6Al composites

Abstract

Interfacial products are well accepted as an important factor to improve the interfacial status and forming quality of short carbon fibers (Csf) reinforced magnesium-7.6 wt% aluminum matrix (Csf/Mg-7.6Al) composites. Understanding the growth mode of the interfacial products to optimize interface reactions plays an essential role in the application of the composites. Here, the growth mode of the interfacial products of the Csf/Mg-7.6Al composites, as well as their thermodynamic properties are deeply investigated. SEM images reveal that a moderate degree of interfacial reactions can be obtained at the fabrication temperature of ∼873 K. TEM images show that the lateral growth rate of the Al4C3 is greater than the longitudinal growth rate. The in-situ Al4C3 phases have an orientation relationship with α-Mg as (012) Al4C3//(101) α-Mg, and their corresponding crystal axis relationship can be determined as [22‾ 1] Al4C3//[21 2‾] α-Mg. The orientation relationship of crystal planes and crystal axis between Mg17Al12 and α-Mg can be seen as (03 3‾) Mg17Al12//(10 1‾) α-Mg and [1 11‾] Mg17Al12//[212] α-Mg, respectively. There are semi-coherent and coherent interfaces between the interfacial products (Al4C3 and Mg17Al12) and α-Mg. More importantly, the standard Gibbs free energy changes of Al4C3 and Mg17Al12 are more negative than other reactions including MgC2, Mg2C3, and Al2MgC2.