Recent advances in grain refinement of light metals and alloys

Abstract

Grain refinement leads, in general, to a decreased tendency to hot tearing, a more dispersed and refined porosity distribution, and improved directional feeding characteristics during solidification. Reduced as-cast grain size can also lead to improved mechanical properties and wrought processing by reducing the recrystallized grain size and achieving a fully recrystallized microstructure. It is now well established that the two key factors controlling grain refinement are the nucleant particles including their potency, size distribution and particle number density, and the rate of development of growth restriction, Q, generated by the alloy chemistry which establishes the undercooling needed to trigger nucleation events and facilitates their survival. The theories underpinning our current understanding of nucleation and grain formation are presented. The application of the latest theories to the light alloys of Al, Mg and Ti is explored as well as their applicability to a range of casting and solidification environments. In addition, processing by the application of physical processes such as external fields and additive manufacturing is discussed.To conclude, the current challenges for the development of reliable grain refining technologies for difficult to refine alloy systems will be presented.

Powder Metallurgy Strategies to Improve Properties and Processing of Titanium Alloys: A Review

“…A suitable microstructure design can be essential to fully exploit the property range of a material. Recent findings provide an important opportunity to advance the understanding of the control of microstructure in PM titanium . Moreover, current investigations offer new insights into the feasible production of wrought‐like PM titanium microstructures…”

3D characterization of ultrasonic melt processing on the microstructural refinement of Al Cu alloys using synchrotron X-ray tomography

“…The Image J [30] software used to adjust the contrast between Fe-rich phases and Al2Cu phase. The 3D segmentation and volume rendering were performed using Avizo Lite v9.0.1 (VSG, 7 France). The 3D bilateral filter was applied to the raw images in order to increase the contrast and reduce noise.…”

Potential of an Al-Ti-MgAl2O4 Master Alloy and Ultrasonic Cavitation in the Grain Refinement of a Cast Aluminum Alloy

“…[2,3] The grain refinement mechanisms as well as some technological issues related to Si or Zr poisoning of Al-Ti-B grain refiners are thoroughly scrutinized by theoretical models and experiments. [11,12] Despite the commercial success of Al-Ti-B and Al-Ti-C grain refiners, some drawbacks are related to their application such as reduced performance in high-Sior Zr-containing alloys and agglomeration of borides in Al-Ti-B master alloys and a narrow process-parameter window for Al-Ti-C master alloys. [1,2,5,6,12] A search for new grain refining systems that may substitute that currently used is ongoing.…”

“…[11,12] Despite the commercial success of Al-Ti-B and Al-Ti-C grain refiners, some drawbacks are related to their application such as reduced performance in high-Sior Zr-containing alloys and agglomeration of borides in Al-Ti-B master alloys and a narrow process-parameter window for Al-Ti-C master alloys. [1,2,5,6,12] A search for new grain refining systems that may substitute that currently used is ongoing. In recent times, interest has grown on using oxides such as Al 2 O 3 , MgAl 2 O 4 , and MgO as nucleation substrates in Al.…”