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In this work, a novel processing method called powder thixoforming was proposed to prepare composites reinforced with 50 vol % of SiC particles (SiCp) that were used for electronic packaging in order to investigate the effects of remelting duration on its microstructure and properties. Optical Microscope (OM), Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) methods were applied for the material characterization and the corresponding physical and mechanical properties were examined in detail. The obtained results indicate that the remelting duration exerted a large effect on the microstructure as well as the SiCp/Al interfacial reaction. The density and hardness of the composite continuously increased with increasing remelting duration. The thermal conductivity (TC) and bending strength (BS) first increased during the initial 90 min and then decreased. The remelting duration exerted a limited influence on the coefficient of thermal expansion (CTE). The optimal TC, BS, and hardness of these composites were up to 135.79 W/(m·K), 348.53 MPa, and 105.23 HV, respectively, and the CTE was less than 6.5 ppm/K after the composites were remelted at 600 °C for 90 min. The properties of the composites could thus be controlled to conform to the application requirements for electronic packaging materials.

Microstructural and mechanical characterization of 10 vol% SiC particles (SiCp) reinforced 6061 Al-based composite fabricated by powder thixoforming (PTF) was investigated in comparison with the PTF and permanent mold cast (PMC) 6061 monolithic alloys. The results reveal that the microstructure of the PMC alloy consists of coarse and equiaxed α dendrites and interdendritic net-like eutectic phases. However, the microstructure of the PTF composite, similar to that of the PTF alloy, consists of near-spheroidal primary particles and intergranular secondarily solidified structures except SiCp, which are distributed in the secondarily solidified structures. The eutectics amount in the PTF materials is distinctly lower than that in the PMC alloy, and the microstructures of the former materials are quite compact while that of the latter alloy is porous. Therefore, the PTF alloy shows better tensile properties than the PMC alloy. Owing to the existence of the SiC reinforcing particles, the PTF composite attains an ultimate tensile strength and yield strength of 230 MPa and 128 MPa, representing an enhancement of 27.8% and 29.3% than those (180 MPa and 99 MPa) of the PTF alloy. A modified model based on three strengthening mechanisms was proposed to calculate the yield strength of the PTF composite. The obtained theoretical results were quite consistent with the experimental data.

A new method, powder thixoforming, has been proposed to fabricate an in situ Al3Tip/2024Al composite. During partial remelting, the microstructural evolution of the bulk alloy prepared by cold pressing of the Ti, Al, 2024Al powder mixture was investigated, and the formation mechanism of the Al3Ti particles produced by the reaction between the Ti powder and the Al alloy melt is also discussed in detail. The results indicate that the microstructural evolution of the 2024 alloy matrix can be divided into three stages: a rapid coarsening of the powder grains; a formation of primary α-Al particles surrounded with a continuous liquid film; and a slight coarsening of the primary α-Al particles. Simultaneously, a reaction layer of Al3Ti can be formed on the Ti powder surface when the bulk is heated for 10 min at 640 °C The thickness (X) of the reaction layer increases with the time according to the parabolic law of \(X = -0.43t^{2} + 4.21t + 0.17\). The stress generated in the reaction layer due to the volume dilatation can be calculated by using the equationσ \(\sigma_{Al_{3}Ti} = -\frac{ E_{Al_{3}Ti} }{6(1-v{Al_{3}Ti})} \frac{ t^{3}_{Al_{3}Ti} }{t_{Ti}} \left(\frac{1}{R} - \frac{1}{R_{0}} \right) \). Comparing the obtained data with the results of the drip experiment, the reaction rate for the Ti powder and Al powder mixture is greater than that for the Ti plate and Al alloy mixture, respectively.