The Role of Grain Refiner in the Nucleation of AlFeSi Intermetallic Phases During Solidification of a 6xxx Aluminum Alloy

Abstract

Primary grain refinement using inoculant additions and intermetallic compound (IMC) phase selection are critical aspects in the solidification of commercial aluminum alloys, controlling the final mechanical properties in service. Although there have been studies which suggest there are explicit interactions between the two phenomena, they have yet to be fully elucidated. Here, through study of intermetallic phase particles extracted from an inoculated casting, key features relating to the nucleation of different intermetallic phases via eutectic reactions are recognized and explained. In particular, rake-like IMCs are identified as initiation points for the deleterious b-AlFeSi IMC phase in a model 6xxx series Al alloy. A mechanism is proposed for how TiB 2 inoculant particles, which are commonly used for primary phase refinement, play a role in enhancing the nucleation of intermetallic phases during eutectic reactions at the liquid/a-Al interface in the final stages of solidification. The implication of this mechanism is that, after the event of primary grain refinement, any unused TiB 2 inoculant particles could be contributing to IMC formation thereby affecting the overall type, size, and distribution of intermetallic phases in the solidified alloy.

In-situ X-ray radiography of primary Fe-rich intermetallic compound formation

“…In AF-B, up to 45% of the primary IMCs were mobile regardless of thermal gradient or cooling rate, suggesting that they nucleated on TiB 2 particles. This provides evidence that TiB 2 can nucleate Fe-rich IMCs (at least as primary phase), as suggested by earlier researchers based on extraction and microscopy [29,44,45].…”

“…It was concluded that nucleation of platelet Fe-rich IMCs was not strongly influenced by the type of particle addition [18]. Extensive IMC extraction and microscopy by Lui et al [29] suggested that TiB 2 from the addition of commercial Al-5Ti-1B might be associated with nucleation of secondary Fe-rich IMCs, evidenced by observation of TiB 2 particles in physical contact with IMC platelets after extraction.…”

Grain Refinement of Alloys in Fusion-Based Additive Manufacturing Processes

“…The free growth model [12] developed by Greer et al is commonly used to determine the potency of particles. [13][14][15] Zhang et al further considered the importance of crystallographic matching by applying their edge-to-edge matching model to explain the effectiveness of grain refiners and have successfully applied this to Al and Mg alloys. [6,[16][17][18] More recently, Fan et al [19] explained the growth of grains by elucidating the mechanisms of heterogeneous nucleation by epitaxial growth from substrates.…”

Segregation in squeeze casting 6061 aluminum alloy wheel spokes and its formation mechanism

“…The segregation of Mg 2 Si and Al 5 Cu 2 Mg 8 Si 6 has been approved by some researchers [12][13][14] , but the formation of AlFeSi phase has aroused great controversy [15][16][17] . The types of the precipitation phase in 6061 alloy based on literature are shown in Table 3 [18][19][20] .…”