The introduction of small amounts of rare earth elements (REE), such as cerium (Ce), into aluminum alloys is an effective way to modify their microstructure and improve mechanical properties. In this paper, the effect of different cerium contents (0.2%, 0.4%, and 0.6% by weight) on the microstructure and thermal expansion coefficient (TEC) of vacuum cast Al-Cu-Fe alloys was investigated.
The experimental technique included melting the alloys in a vacuum furnace with subsequent chill casting. Microstructural analysis was performed using optical and electron microscopy. The phase composition was determined by X-ray phase analysis (XPA). The CTE was measured by the dilatometric method in the temperature range from 25 to 500 °C.
The results showed that the addition of cerium has a significant effect on the microstructure of Al-Cu-Fe alloys. The introduction of 0.2% Ce leads to grain refinement and a more uniform distribution of intermetallic phases. With an increase in the cerium content to 0.4%, further refinement of the structure and the formation of new cerium-containing phases are observed. A further increase in the cerium content to 0.6% leads to some coarsening of grains and the formation of large inclusions of cerium-containing phases along the grain boundaries.
CTE measurements showed that the addition of cerium reduces the CTE of Al-Cu-Fe alloys. The lowest CTE value was observed for the alloy containing 0.4% Ce. This is explained by the formation of cerium-containing phases having a lower CTE compared to the aluminum matrix.
Low thermal expansion alloys play a key role in the creation of modern materials for aviation and astronautics. This paper presents the results of studying various quasicrystalline alloys containing rare earth elements obtained by vacuum casting. The aim of the study was to systematically study the effect of cerium (Ce) addition on the structure, thermal properties and microhardness of the Al-Cu-Fe alloy.
During the experiments, a new microstructure of Al-Cu-Fe-Ce was revealed. It was found that increasing the concentration of added Ce leads to a more uniform distribution of phases. The lowest coefficient of thermal expansion of the alloy was recorded with the addition of 1 atomic percent of cerium. In this state, the alloy demonstrated maximum microhardness.
The microhardness of alloys with 1 at.% cerium was approximately 2.4 times higher than that of alloys without cerium addition. The reduction in the thermal expansion coefficient was approximately 20%. Thus, the use of vacuum casting in combination with the addition of an optimal amount of cerium opens up prospects for the development of new Al-Cu-Fe-Ce alloys with improved characteristics.
Thus, the introduction of cerium into Al-Cu-Fe alloys cast by vacuum casting allows modifying their microstructure and reducing the CTE. The optimum cerium content for achieving the best properties is 0.4% by weight.
Author: Huang Wang, Zhong Yang, Zhijun Ma, Yelping Bai, Hongbo Duan, Dong Tao, Guoqing Shi, Jiachen Zhang, Zhen Wang and Jianping Li
Institute: School of Materials Science and Chemical Engineering, Xi’an University of Technology, Xi’an 710021, People’s Republic of China