Interfacial reactions between Al7075 alloy and BaAl₂Si₂O₈ + CaAl₂Si₂O₈ mixture

Abstract

The present work reports the SEM, EPMA and TEM examination of reactions at the interface of Al7075 alloy and a 50/50 wt% mixture of BaAl₂Si₂O₈ + CaAl₂Si₂O₈ feldspars at 850 °C, 1150 °C and 1250 °C. Sintering of the feldspar mixture at 1450 °C caused dissolution of ~1.0 wt% Ca in BaAl₂Si₂O₈ and 0.5 wt% Ba in CaAl₂Si₂O₈. The interaction of the Al alloy with the sintered feldspars shifted the alloy composition to the Al–Si–αBaAl₂Si₂ and Al–Si–βaAl₂Si₂ compatibility triangles. The feldspars underwent a series of phase transformations, leading ultimately to the formation of Al₂O₃.

Keywords:

• Aluminium alloys
• corrosion
• diffusion
• interfacial
• phase transformations

Notes

1. The radii for the ions in the present work are crystal radii [21].

2. Although TEM analyses were used in both transmission and scanning modes, only the STEM mode results are presented.

3. In the present work, celsian and anorthite are treated as stoichiometric phases for simplicity and the formation of spinel was disregarded owing to the low activity of Mg in the alloy