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Studies on microyield behavior of SiCp/2024Al composite materials

Microyield behavior of silicon carbide particles reinforced 2024 aluminum alloy (SiCp/2024Al composites) with three volume fractions of SiCp were investigated in this paper. The results of the studies showed that the composites exhibited some types of notable strain relaxation before microyielding when subjected to an applied stress far lower than conventional yielding stress. The microyield mechanism did not conform to the classical linear relation between the applied stress (σ) and square root of plastic strain (εp ½), proposed by Brown and Lukens. Microyield strength could be strongly affected by heat treatment routes. The thermal processing with large temperature change, such as high temperature quenching or annealing, rapid cooling to liquid nitrogen temperature, thermal cycling with large upper-lower cyclic temperature interval, etc., would lead to deterioration of microyield strength, whereas an appropriate aging treatment would significantly increase microyield strength of the SiCp/2024Al composites. TEM and X-ray diffraction analyses revealed the relationship between microyield behavior and microstructures. In general, dispersed strengthening phase S′, lower residual stresses and lower population of movable dislocations would be beneficial to microyield strength of the SiCp/2024Al composite materials. The effect of SiCp on microyield strength was dependent to thermal processing history.