Simultaneously improving thermal conductivity and mechanical properties of Al-Si alloys: Based on the influence of microscopic defects and second phase

To reveal the combined effect of defects and second phases on the thermal conductivity of Al-Si alloys, the defects and second phase of materials heat treatment was controlled by cryorolling and heat treatment. The correlation between thermal conductivity, grain boundaries, the morphology of the second phase, and dislocations was studied in this work. The results indicate that the Al-Si alloy possesses the highest thermal conductivity after heat treatment following 15% deformation, with an 11.8% increase compared to the as-cast alloy and a 59.44% increase in tensile strength. At 15% deformation, increased grain boundary density and dislocations due to grain fragmentation increased the probability of scattering of electrons and phonons, thereby limiting electron and phonon conduction. Nevertheless, electrons demonstrate a proclivity for traversing pathways with low resistivity to avoid passing through more grain boundaries, this reduces the effect of grain boundaries on electron conduction. The enhancement in thermal conductivity resulting from the decreases of second phase size has not been completely negated by the effectiveness of grain refinement. After the heat treatment, a large number of dislocations disappeared, and the second phase was broken into smaller segments and gradually spheroidized, which improved the electron and phonon conduction. Furthermore, the mechanical properties were also improved by dispersion strengthening and grain refinement strengthening. This work delved into the mechanism by which second phases and defects affect the thermal conductivity and mechanical properties of the alloys and provided an important theoretical basis for further research.