Fabrication And Properties Of Sicp/2024al Composite Foams

SiCp/2024Al composite foams were fabricated by powder metallurgy using calcium carbonate as foaming agent. The fabrication technology, compression behavior and damping properties of the composite foams were researched. In the process of the fabrication of SiCp/2024Al composite foams, firstly characteristics of thermal decomposition of CaCO₃ were researched by Differential Scanning Calorimetry(DSC), and then the situation that the porosity and the average pore dimension were influenced by the hot extrusion of precursor materials, the volume fraction of foaming agent, the temperature of foaming, the holding time and the volume fraction of SiC particles were investigated. Quasi-static compression experiments of SiCp/2024Al composite foams were tested on Gleeble 1500 thermal simulation testing machine, the situation that the quasi-static compression properties were influenced by the structure of pore and the volume fraction of SiC particles were analyzed. The damping properties were investigated by the damping-strain and damping-temperature capacity of SiCp/2024Al foams tested on dynamic mechanical thermal analyzer (DMA).CaCO₃ started to decompose around 600℃by the DSC experiments, and the decomposition rate accelerated when the temperature increased. The time of complete decomposition of CaCO₃ was 24, 19, 8 and 6 minutes respectively at 660, 680, 700 and 720℃. The precursor materials containing SiC particles and CaCO₃ by powder metallurgy were hot extruded. The observation of microstructure showed uniform distribution of SiC particles and CaCO3. This benefited the nucleation and growth of the bubble. The research of the volume fraction of CaCO₃ showed that the porosity of foams was low while the volume fraction of CaCO₃ was small, the uniformity of pore structure got worse. With temperature and holding time increasing, the porosity showed the trend that increased first and decreased later, but the average pore dimension always inlarged. The uniformity of pore structure got worse, and more pores interconnected to form a gap. SiC particles increased the viscosity of liquid Aluminum. This resulted the resistance of the movement of the gas-liquid interface increased. In the process that the volume fraction of SiC changed from 0 to 10%, the porosity and pore size of foams decreased under the same foaming conditions.In the quasi-static compression, Aluminum composite foams had a characteristic compression stress-strain curve. It was consisted of three distinct regions: linear elastic, collapse and densification. Al foams compression stress-strain curve was smooth. Hower, the yield platform of the stress-strain curve appeared jagged fluctuations, because the SiC particles increased the brittleness of the matrix. The content of SiC almost didn't change the length of the yield platform, but increased the compressive yield strength and energy absorption capacity. While the porosity increasing, the compressive yield strength of SiCp/2024Al foams decreased, the length of the yield platform increased, energy absorption capacity decreased.The damping-strain capacity of SiCp/2024Al foams had the typical characteristics of the dislocation damping. As the porosity increased, SiCp/2024Al foams damping properties increased first and then decreased. Two damping peaks of the damping-temperature capacity were found in the 250²80℃and 330³85℃temperature range, which were denoted as P1 and P2. It was proved that P1 was the peak of dislocation damping and P2 was the peak of grain boundary or interface damping. As the porosity increased, the height of P2 peak dereased and the location moved to the high temperature. The addition of SiC particles increased the damping of room temperature.