Relationship Between Microstructure and Mechanical Behavior of Cast Composite Materials with In Situ Intermetallic Reinforcement

The purpose of this study is to analyze the relationship between the parameters of the microstructure and the mechanical behavior of cast composite materials of the Al-Al₃Ti system, considering modern representations about the mechanisms of their structure formation and strengthening. 

Methods. Cast composite materials with endogenous intermetallic reinforcement were obtained by adding compacted titanium powder (>99.5% Ti) with a size of <300 μm in an amount of 3 wt.% into an aluminum melt of the composition Al + 7 wt.% Zn + 3 wt.% Mg. To study the obtained materials, computer methods of quantitative metallography and the method of measuring hardness were used. The relationship between the microstructure and mechanical behavior of aluminum matrix composites was analyzed using generally accepted theories of reinforcing.

Results. It is shown that during direct chemical interaction between powdered particles of metallic titanium with an aluminum melt of the Al-Zn-Mg system, the formation of dispersed Al₃Ti particles uniformly distributed over the volume of the material occurs. The synthesized particles had an average size of 11.42 µm and occupied an area fraction of 10.27%. The formation mechanism of Al₃Ti reinforcing particles is considered. The average values of the hardness of samples of aluminum matrix composites in the as-cast state were 141.6 HB, while the hardness of the unreinforced matrix was 92 HB. An analysis was made of the potential mechanisms of strengthening of cast composite materials that determine their mechanical behavior in conjunction with the processes of structure formation.

Conclusion. Direct synthesis of aluminum matrix composites with endogenous intermetallic reinforcement by adding compacted powder precursors into the matrix melt made it possible to achieve an excellent degree of uniformity in the distribution of reinforcing particles without the use of special technological equipment. Presumably, the predominant mechanism of strengthening of cast composite materials of the Al/Al₃Ti system should be considered strengthening due to a mismatch between the thermal expansion coefficients and elastic moduli of the components and Hall-Petch strengthening due to the modifying action of Al₃Ti particles with respect to crystals of the α-solid solution of matrix aluminum alloys.

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