Abstract
An experimental and theoretical investigation of the strength properties of aluminum alloys strengthened by dispersed nanoparticles, as well as the determination of the significance of various mechanisms responsible for the strengthening of the material, was carried out. Results of experimental investigation demonstrate that the hardening of aluminum alloy A356 by Al2O3 and ScF3 nanoparticles leads to an increase in the yield strength, ultimate tensile strength, and plasticity. Despite the similar size of Al2O3 and ScF3 nanoparticles, the physicomechanical properties of nanoparticles significantly affect the possibility of increasing the mechanical properties of the A356 aluminum alloy. A physicomathematical model of the occurrence of thermal stresses was developed caused by the mismatch of the coefficients of thermal expansion (CTEs) of the matrix and strengthening particles on the basis of the fundamental principles of mechanics of a deformable solid and taking into account the elastic properties of not only the matrix, but also the particle. The forming of thermal stresses induced due to the mismatch of the coefficients of thermal expansion of the matrix and the strengthening particle in aluminum-based composites was investigated. In the case of thermal deformation of dispersion-hardened alloys, when the CTE of the matrix and particles noticeably differ, an additional stress field is created in the vicinity of the strengthening particle. Thermal stresses increase the effective particle size. This phenomenon can significantly affect the result of the assessment of the yield strength. The strengthening caused by thermal mismatch makes the largest contribution to the yield strength improvement. The yield strength increments due to Nardon×Prewo and Orowan mechanisms are much lower.
Highlights
Aluminum-based alloys are widely used in the automobile industry because they are castable in complex forms and because of their excellent wear resistance, light weight, and good strength, which make them widely used in the manufacture of numerous automotive parts, such as engine blocks and wheels
ScF3 nanoparticles are concentrated in the A356 aluminum alloy around the silicon inclusions (Figure 2c,d) and along the grain boundaries
A considerable improvement in yield strength of the composite was recorded with integration into the improvement in yield strength of the composite was recorded with integration into the matrix of the 1% Al2 O3 and 1% ScF3 disperse phase
Summary
Aluminum-based alloys are widely used in the automobile industry because they are castable in complex forms and because of their excellent wear resistance, light weight, and good strength, which make them widely used in the manufacture of numerous automotive parts, such as engine blocks and wheels. According to continuum linear elastic dislocation theory, Orowan [7] proposed that the interaction between dislocation and hardening particles leads to the formation of shear loops around the particles. This dislocation interaction scenario leads to what is known as Orowan strain hardening. Humphreys and Hirsch [11] proposed an alternative mechanism in which, if all dislocations are edge-oriented, each dislocation/particle interaction leads to two pairs of prismatic loops, one on each side of the particle. The material hardening depends on the types of particles, their volume fraction and homogeneous distribution in the matrix, and the interaction between matrix and strengthening particles
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