In-Situ  Processing of Composites

Discontinuously Reinforced Aluminum-based Composites (DRACs) are listed among the most promising structural materials owing to their lightweight and improved mechanical properties including wear resistance. The DRACs manufactured by traditional solidification and powder metallurgy methods so far, however, are still not profitable, in comparison with the widely used structural steel parts. In traditional techniques, expensive reinforcing particles manufactured separately are used. The objective of this project is to develop an in-situ molten metal technique, through which the reinforcing particulates such as SiC and AlN are formed in-situ in the aluminum alloy matrix with low cost and improved reinforcing properties.

To develop this novel technique, thermodynamic properties of the reinforcements in Al alloy matrix, and the influence of process variables on the formation of equilibrium reinforcing particulates were modeled using Gibbs energy minimization method. It is found that the thermodynamic stability of SiC in Al-alloy matrix is affected by the compositions of the alloy matrix and temperature. AlN is thermodynamically stable in Al-Si alloy over the whole range of processing and application temperatures. Experimental studies showed that the novel molten metal technique is technologically feasible. The reinforcing particulates formed in-situ were small in size and were uniformly dispersed in the alloy matrix. It was also found that the formation of reinforcing particulates was influenced by the composition of alloy matrix, temperature, N2 gas bubble size, and the oxygen content in the bubbling gas.

The work in progress includes the development of a kinetic model to understand the process mechanism, investigation of the microstructure and properties of the DRACs, and optimization of the materials and process parameters.