Certain metal matrix composite systems allow designers to produce materials with tailored properties, such as a desired co-efficient of thermal expansion for electronics packaging.
Other key factors leading to the possible commercial use of such materials are the abilities to be able to manufacture them cost effectively and to tight dimensional tolerances. Silicon carbide reinforced aluminium has become a popular system for these reasons.
Manufacturing Al/SiC Metal Matrix Composites
Conventional Manufacturing Techniques
Initially conventional metals processing techniques such as extrusion, gravity casting and vacuum casting were used to produced Al/SiC MMC’s. Finished products were then produced from the ingots or billets.
These materials were in effect produced by suspending silicon carbide particles in the molten aluminium. The biggest technical problems associated with these techniques involved maintaining dispersion of the ceramic particles within the metal matrix. Further the silicon carbide content had to be limited to to avoid separation. As such the maximum ceramic content was about 30%.
Despite the limitation on ceramic content, the Al/SiC materials were produced with lower co-efficients of thermal expansion and improved strength and thermal conductivity compared to unreinforced aluminium.
Using patented processes, Al/SiC MMC’s can be manufactured with silicon carbide contents as high as 63volume%.
The first process Quick-SetTM produces a porous net shaped ceramic item in silicon carbide using a low pressure, low viscosity injection moulding process. This is followed by pressure assisted infiltrations of the ceramic form by molten aluminium by a process called Quick- CastTM.
The process features:
• The ability to use different material combinations
• The ability to produce complex shapes
• Low tooling costs
• No need for secondary machining operations