Abstract
The naturally formed inclusions in an Al-3Fe alloy were investigated using a pressurized melt filtration technique. Naturally formed AlN particles with a rodlike morphology and a size distribution between 200 nm and 4 µm coexist with the native Al2O3 particles in the Al-3Fe alloy. These native AlN particles were investigated with scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). A well-defined orientation relationship (OR) between AlN and α-Al was found from the AlN particle embedded in α-Al. A tilt angle of 5.8 deg was observed between {111}α-Al and {0001}AlN at the α-Al/AlN interface. The atomic matching for the α-Al/AlN interface was investigated by considering interfacial segregation on the AlN particles. The heterogeneous nucleation potency of the native AlN particles was investigated. Although these native AlN particles can nucleate the α-Al, the contribution is very small. This contribution reveals the heterogeneous nucleation of α-Al on the native AlN particles and the competitive relationship between the native Al2O3 and AlN as the nucleation substrates. The surface modification of the native AlN in Al alloys containing multiple alloy elements and the corresponding effects on the heterogeneous nucleation were preliminarily investigated.
Highlights
THE naturally forming inclusions in Al melts were generally considered to be harmful to casting alloys, as these large inclusion films in the melts generate casting defects
The magnified image (Figure 1(b)) shows that the primary Al13Fe4 phase has starlike morphology and the associated binary eutectic-Al13Fe4 connected with the primary Al13Fe4 particles
A large number density of a-Al2O3 was observed as the major native inclusions, and a smaller number density of native AlN particles was observed along the double-side oxide films in an Al-3Fe alloy
Summary
THE naturally forming inclusions in Al melts were generally considered to be harmful to casting alloys, as these large inclusion films in the melts generate casting defects. With the recent developments in heterogeneous nucleation theory,[1,2,3,4] pathways are developed to use these inclusion particles to nucleate a-Al and primary intermetallic phases. Melt conditioning technologies, such as intensive melt shearing,[5, 6] which aims to break the inclusion films and distribute the particles uniformly through the melt, have been developed. AlN was observed to naturally form in Al-3Fe alloy and coexist with Al2O3 particles.
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