The interplay of precipitation of ordered compounds and interfacial segregation in Al-Cu-Hf-Si alloys for high-temperature strength

Achieving high yield strength (250-270 MPa) at elevated temperatures (250 degrees C and above) for precipitation strengthened aluminium-copper (Al-Cu) alloys still remains a challenge for the alloy designers. This paper presents a systematic progression of the microstructure evolution in a binary Al-0.3Hf, ternary Al-0.3Hf-0.3Si and quaternary Al-2Cu-0.3Hf-0.3Si (in at%) alloys. A quantitative understanding of the role that Hf and Si plays in promoting ordered precipitates and the metastable Al-Cu intermetallic compounds 0/ 0' has been attempted. The initial microstructure is guided by the initial precipitation of primary phases, triggering the formation of Hf-rich dendrites and finally, the Si/Cu segregation at boundaries. Ageing of binary Al-Hf alloy results in precipitation of L1 2 ordered phase via discontinuous (cellular) process. Si, however, promotes a continuous precipitation process, resulting in the formation of coherent and spherical L1 2 ordered phase in the matrix. The role of these ordered precipitates in influencing the precipitation of 0/ 0' compounds in quaternary copper containing alloy was explored in detail, including their coarsening and mechanical properties at elevated temperatures. The compact morphology developed in the alloy results in yield strength of 445 +/- 8 MPa at room temperature (25 degrees C). The yield strength evolves through the interaction of L1 2 and 0/ 0' ordered phases with the a-Al matrix. The coarsening of 0' phase was slowed down due to Hf segregation at a semi-coherent interface and led to a thermally stable microstructure that resulted in yield strength of 256 +/- 8 MPa at 250 degrees C. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study systematically investigates the microstructure evolution in Al-Cu alloys and explores the role of Hf and Si in ordered precipitates and intermetallic compound formation. With the promotion of Si, coherent and spherical ordered phases can be formed in the alloy matrix. These ordered precipitates play a significant role in the precipitation of metastable compounds in copper-containing alloys and exhibit good mechanical properties at elevated temperatures.