Aluminum Matrix Composites Fabricated By In-situ Reaction Technology In Al-ZrO₂, Al-ZrO₂-B Systems

In this article,Al-ZrO₂ and Al-ZrO₂-B systems aluminum matrix composites were fabricated by means of exothermic dispersion(XD).Thermodynamic analysis of reaction process was carried out.The reaction products and microstructures of composites were analysed by modern means such as optical microscope(OM),scanning electron microscopy (SEM),and X-Ray diffraction(XRD).The kinetics of the reaction process was investigated based on DSC and the influence of different technical parameters on the reaction process and results;the normal temperature mechanical performance was tested and its strengthening mechanism and fracture mechanism were explored.The study of mechanism shows that:with the raise of temperature,Al liquefied and formed fluid-solid interface with ZrO₂;when the temperature reached 830℃,α-Al₂O₃,which has stable thermodynamic properties,and active Zr atoms were produced.In Al liquation, owing to its poor wettability,α-Al₂O₃ particles were prone to segregate at the interface and hindered Zr atoms' dispersion;however,with the effect of concentration gradient and heat,Zr atoms diffused into Al matrix and then Al₃Zr generated.In Al-ZrO₂-B system,firstly B reacted with Al at 700℃to form AlB₂;as warming up to 840℃,AlB₂ reacted with ZrO₂ to generateα-Al₂O₃ and ZrB₂,which inhibited the formation of Al₃Zr.When B/ZrO₂ molar ratio was 2,Al₃Zr basically disappeared in the matrix;the reaction product only consists ofα-Al₂O₃ and ZrB₂.The activation energy value of Al-ZrO₂ system calculated from DSC curves with different heating rates and the Kissenger equation was shown to be 358 kJ/mol. When B/ZrO₂ molar ratio is 1,the activation energy rise to 393 kJ/mol.The research of mechanical properties shows that:as B/ZrO₂ molar ratio grew from 0 to 1,further to 2,the tensile strength of the composites whose reinforcement volume fraction were 20%and 30%firstly decrease from 135MPa and 186MPa to 130MPa and 163MPa respectively,but then rose to 189MPa and 209MPa.However,the elongation rate varied in the opposite way,increasing from 4.7%and 14.9%to 10.3%and 16.1%at first,and then falling to 8.1%and 12.3%.The strengthening mechanism of Al-ZrO₂ and Al-ZrO₂-B systems composites can be interpreted by dispersion strengthening,fine grain strengthening, dislocation strengthening;the fracture mechanism include dislocation nucleation mechanism and the vacancy mechanism.