On the technique of prolonged thermal exposure of Al-alloys – Static and Dynamic techniques are almost the same!

Significance 

Aluminum alloys are widely used in numerous applications such as automobile engines owing to their excellent mechanical properties. However, aluminum alloys are susceptible to mechanical degradation when exposed to high temperatures due to the induced microstructural changes. Going with the current trend, the use of aluminum alloys under high temperatures is expected to increase. Therefore, enhancing the high-temperature performance of aluminum alloys is highly desirable.

In a recently published literature, Al-Si-Cu-Mg cast alloys have been identified as suitable alternatives for high-temperature applications. Unfortunately, the effect of prolonged exposure to elevated temperatures on the mechanical properties of these alloys has not been fully explored. Alternatively, the addition of transition elements has been identified as a promising solution for controlling the alloy microstructure to improve their properties. Among the available transition elements, Zirconium is widely used with aluminum alloys due to their ability to form stable precipitates to prevent precipitates coarsening under high temperatures.

To this note, Dr. Abdelaziz and Professor Fawzy Samuel from University of Québec in Chicoutimi together with Dr. H.D. Doty from General Motors Company and Dr. Salvador Valtierra from Nemak-Mexico investigated the effects of adding transition elements on the mechanical performance of Al-Si-Cu-Mg cast alloys under the prolonged exposure to elevated temperatures. They also employed static (continuous) and dynamic (interrupted) exposure techniques to describe the material behaviors and their corresponding effects on mechanical properties. In particular, they used several techniques such as transmission electron microscopy to examine and evaluate the associated morphological changes of the strengthening precipitates. Their research work is currently published in the journal, Materials Science and Engineering A.

In brief, the collaborative research team initiated their studies by cross-examining the effectiveness of adding Zr, Ni and Mn transition metals in controlling the microstructure of Al-Si-Cu-Mg cast alloys. Next, they varied the thermal exposure technique from static to dynamic and analyzed its influence on the mechanical behavior of the alloys. Lastly, a case study was performed to compare the influence of dynamic and static exposure of the transition elements on the mechanical properties of the alloys.

The authors observed that varying thermal exposure technique had insignificant influence on the mechanical properties of the alloys and especially tensile and hardness properties. On the other hand, an increase in the ductility and decrease in the yield strength were noted to be as a result of heating and subsequently the coarsening of precipitates at a temperature of 250°C for a longer time. In addition, the simulated results illustrated the real-time behavior of the material under dynamic thermal exposure.

One more interesting observation, the degradation in strength values and the associated increase in the values of elongation to fracture were clearly noticeable in the first 100 hours of thermal exposure. However, the second 100 hours of exposure (i.e. from 100 hours till 200 hours) did not witness a considerable variations in the mechanical properties of the alloys under investigation.

In summary, the study demonstrated the effectiveness of adding Zr, Ni and Mn elements in enhancing the mechanical performance of Al-Si-Cu-Mg cast alloys based on the static and dynamic exposure techniques; besides the fact that varying the stabilization technique did not significantly affect the results. Altogether, the study provides vital information that will advance future work in improving high-performance aluminum alloys in high-temperature applications such as automotive engine components.

About the author

M. H. Abdelaziz is currently an assistant professor at the French University in Egypt (UFE). In 2018, He received his PhD in Manufacturing and Materials Engineering from University of Quebec at Chicoutimi (UQAC), Canada. Dr. Abdelaziz received his MSc and BSc degrees in Mechanical Design and Production Engineering from Cairo University, Egypt in 2012, and 2006, respectively.

His research focuses on the development and characterization of light innovative materials aiming at reducing harmful emissions and promoting greener societies. Specifically, he is interested in metallic alloys and composite materials that can be achieved via casting and additive manufacturing techniques.

Reference

Abdelaziz, M., Doty, H., Valtierra, S., & Samuel, F. (2019). Static versus dynamic thermal exposure of transition elements-containing Al-Si-Cu-Mg cast alloyMaterials Science and Engineering: A739, 499-512.

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