On the grain refinement of aluminum alloys
Abstract
Aluminum grain refinement has been widely used by aluminum alloy manufacturers more than 60 years. It primarily consists of adding aluminum master alloys to pure aluminum or aluminum alloy melts. The purpose of adding the grain refiner is to make alloy castable for ingots and castings by reducing grain size to prevent hot tearing from formation. However, there is still no agreement on the mechanism of the grain refinement process despite availability of the nucleate and solute paradigms. The nucleant paradigm supporters believe that finer grain size is the result of adding foreign particles as nucleant sites for grain refinement while the solute paradigm supporters suggest that the segregation ability of the solute elements is the main reason of refinement. This study briefly examines the paradigms and moves on to develop a new approach for evaluating the mechanism and effectiveness of aluminum in grain refinement. Popular grain refiners Al-3Ti-1B and Al-5Ti-1B from different manufacturers have been used in this study to test their effectiveness. The criteria for grain refinement based on the growth restricting factors have been discussed and compared with experimental data in the study. Detailed microscopic evaluations of the test samples show the effectiveness of grain refiner by comparing the grain size. Furthermore, the morphologies of compound particles, such as TiB 2 and Al3Ti, in different grain refiners and from different makers have been observed by deep etching and SEM images. The function and formation of the compound particles on grain refinement of aluminum alloys are also discussed in the paper.
Degree
Ph.D.
Advisors
Han, Purdue University.
Subject Area
Mechanical engineering|Materials science
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