[X-MAT]’s Master Thesis of Sandra Gonzaga is now online!

Exploring Alloys in the Al-Mg-Si System for Space Applications

The Master Thesis of our postgraduate researcher Ms. Sandra Gonzaga is now online and available for download at: https://pureadmin.unileoben.ac.at/portal/en/publications/development-and-characterisation-of-an-ultrafinegrained-almgsi-alloy-for-space-applications(5be5ba38-321f-47bf-99e5-4f72ccebef4e).html?customType=theses

In the race to conquer the cosmos, materials science plays a pivotal role in enabling the development of spacecraft and satellites capable of withstanding the harsh realities of space. In Sandra’s research we delved into the Al-Mg-Si alloy system, focusing on its potential for space applications. Aluminum and its alloys, renowned for their lightweight and high-strength properties, have emerged as strategic materials for future space programs. Their ability to undergo age-hardening to enhance strength makes them particularly promising. However, the challenges posed by the space environment, particularly radiation-induced degradation, necessitate innovative solutions.

Key Requirements for Space-Grade Alloys

For an alloy to thrive in space, it must exhibit:

High strength-to-weight ratio: Essential for optimizing payloads.
Thermal performance: To endure extreme temperature variations.
Radiation resistance: Protection against degradation caused by solar energetic particles.

While aluminum alloys meet many of these criteria, their performance under prolonged energetic particle irradiation can suffer due to precipitate dissolution and the formation of dislocation loop networks.

The Role of Ultrafine-Grained (UFG) Aluminum Alloys

To mitigate radiation-induced damage, UFG aluminum alloys have been proposed as a solution. Their abundant grain boundaries facilitate the rapid annihilation of radiation damage, making them a suitable candidate for space applications. However, achieving high thermal stability against recrystallization in UFG alloys remains a formidable challenge.

Synthesis and Analysis of UFG AA6061 Alloy

Sandra’s research focused on synthesizing a UFG AA6061 alloy using high-pressure torsion (HPT), a severe plastic deformation (SPD) technique. After successful synthesis, she explored the precipitation behavior in UFG AA6061 compared to its coarse-grained (CG) counterpart using:

Differential Scanning Calorimetry (DSC): For thermal analysis.
Scanning Transmission Electron Microscopy (S/TEM): For microstructural characterization.
In situ TEM experiments: To study thermal stability and recrystallization behavior.

Key Findings

Precipitation Behavior:
Precipitation hardening in UFG AA6061 alloys depends significantly on grain size.
The UFG alloy exhibited accelerated precipitation compared to the CG alloy.
Metastable phases, such as beta” (reading beta-double-prime), were absent in the UFG alloy. The equilibrium phase beta formed rapidly at lower temperatures.

Thermal Stability:
Precipitation in UFG AA6061 occurs primarily at intra-granular positions, resulting in low volumetric densities.
These characteristics led to recrystallization of the UFG microstructure at approximately 180°C.

Comparison with novel AlMgZnCuAg crossover alloys:
Unlike UFG AA6061, UFG crossover alloys like AlMgZnCuAg demonstrated superior grain boundary stability due to the high-density T-phase precipitates. The highly negative enthalpy of T-phase formation restricted grain boundary movement and delayed recrystallization.

Implications for Space Applications

Sandra’s work underscores the potential of UFG aluminum alloys, particularly AA6061, for space applications. However, it also highlights critical differences between UFG AA6061 and advanced UFG alloys such as AlMgZnCuAg. These differences shape their suitability for specific space missions. While UFG AA6061 excels in certain areas, further refinement is needed to overcome challenges like recrystallization and precipitation density.

Conclusion

The study advances our understanding of how UFG aluminum alloys behave under space-relevant conditions, paving the way for the development of next-generation materials capable of supporting humanity’s aspirations in space exploration.