Recycling of an Aluminium-based Composite 
using Disintegrated Melt Deposition Technique

Metal matrix composites (MMCs) provide the opportunity to combine the metallic properties of the matrices with the ceramic properties of the reinforcements, leading to greater modulus, strength, wear resistance and thermal stability. They are a new class of materials suitable for advanced structural, aerospace, automotive, electrical, thermal management and wear applications. Commercially, producers have concentrated on composites with particulate reinforcement because of cost issues. Currently, the most common type of MMC is silicon carbide particulates in aluminium-based matrix.

Given the limited natural resources and the ever increasing demand for energy and materials, along with accumulating waste has forced us to think about recycling as a solution. In the present study, Al/SiC composite was synthesized and recycled using the Disintegrated Melt Deposition (DMD) technique. The DMD process is a modification of the more conventional dispersion and spray processes. This method of processing circumvents the disadvantages associated with the dispersion and the spray processes. The deposited composites were secondarily processed by hot extrusion. Microstructural characterization and mechanical properties determination were conducted using scanning electron microscopy and tensile testing, respectively.

Chemical analysis was employed to determine the weight percentage of reinforcement in the composites and it was found that the recycled composites contain slightly less SiC. However, they have a lower level of porosity when compared to the originally fabricated composite (Table 1). Microstructural characterization studies revealed that the original and recycled composites had similar grain morphology, uniform distribution of SiC and good interfacial integrity between the matrix and the reinforcement (Figure 1).

Table 1: Results of Characterization Studies.

Process

SiC (wt%)

r (g/cm3)

Porosity (Vol%)

New

12.9

2.73

0.93

Recycled 1X

12.8

2.74

0.45

Recycled 2X

12.2

2.73

0.75

For the ambient mechanical properties of the composites, tensile testing results (Table 2) revealed that the recycled composites had superior elastic modulus (E), 0.2% yield strength (0.2% YS), ultimate tensile strength (UTS) and ductility. This can be attributed to the improved density of the composites as well as good interfacial integrity. Work is currently continuing to establish the relationship between microstructure and mechanical properties.

Table 2: Summary of Mechanical Properties.

Process

E (GPa)

0.2% YS (MPa)

UTS (MPa)

Ductility (%)

New

77

94

117

4.7

Recycled 1X

85

104

135

7.5

Recycled 2X

83

112

138

6.4

In conclusion, the DMD technique was successfully utilized to synthesize and recycle Al/SiC. Recycling through the DMD technique has no adverse effect on the properties of the MMC and has in fact, shown to be able to improve the mechanical properties of the composite.



(a)


(b)

Figure 1: Representative SEM micrographs of Al/SiC (Recycled 1X) showing (a) distribution of SiC and (b) interfacial integrity between the matrix and the reinforcements.

Contact Person: Assoc Prof M Gupta 
Tel: 874 6358, Fax: 779 1459
Email: mpegm@nus.edu.sg