I would say both composites , SiC &Al2O3, have the same strength & corrosion resistance.   However, the price of Al2O3 is more than SiC composites. 

Both the reinforcements produce almost similar properties in MMCs. i can say that the mechanical properties like tensile strength, impact toughness, hardness etc. for SiC reinforced MMCs is slightly better than that of alumina reinforced MMCs. The cost of SiC particles is higher than that of the alumina particles (microns).

The widely used reinforcing materials for these composites are silicon carbide, aluminum oxide and graphite in the form of particles or whiskers. The ceramic particles reinforced aluminum composites are termed as new generation material and these can be tailored and engineered with specific required properties for specific application requirements. Particle reinforced composites have a better plastic forming capability than that of the whisker or fiber reinforced ones, and thus they have emerged as most sought after material with cost advantage and they are also known for excellent heat and wear resistance applications. the castings of the base alloys were carefully machined specimens for density, hardness, mechanical, tribological tests and as well as for microstructural studies as per ASTM standards. The SiC and Al2O3 resulted in improving the hardness and density of their respective composites. Further, the increased %’age of these reinforcements contributed in increased hardness and density of the composites. The microphotographs of the composites studied revealed the uniform distribution of the particles in the matrix system.

To be precise  in answering ur question is

·         aluminium metal matrix composites with aluminium oxide (Al2O3) as particle reinforcements have higher density values compared to Aluminium metal matrix composites with Silicon Carbide (SiC) as particle reinforcements, since the density value for aluminium oxide (Al2O3) is relatively higher than that of silicon carbide (SiC).

·         Al-SiC composites exhibit relatively higher hardness and tensile strength compared to Al-Al2O3 composite materials for 10% and 15% particle reinforcements.

·         aluminium metal matrix composites with SiC as reinforcement particles have lower wear rates compared to aluminium metal matrix composites with Al2O3 reinforcement particles,

·         the wear rate decreases significantly with the increase of particle reinforcements for both type of composite materials.

·         For instance, the wear rate for Al with 15% SiC composite is about 50% of the wear rate of 1005 Al . The wear rate decreases significantly with the addition of reinforcement particles. Al-SiC composites exhibit lower wear rate compared to Al-Al2O3composites.

You may refer the following articles which compare several reinforcement particles.

Journal of Materials Research and Technology, 5 (2016) 302–316. (https://www.researchgate.net/publication/301310838_Effect_of_ceramic_particulate_type_on_microstructure_and_properties_of_copper_matrix_composites_synthesized_by_friction_stir_processing)

Journal of Asian Ceramic Societies, 4 (2016) 209–218. (https://www.researchgate.net/publication/301754938_Influence_of_ceramic_particulate_type_on_microstructure_and_tensile_strength_of_aluminum_matrix_composites_produced_using_friction_stir_processing?ev=prf_high)

Article Effect of ceramic particulate type on microstructure and pro...

Article Influence of ceramic particulate type on microstructure and ...

 Thank you all. They are very helpful.

Overall there is not a clear answer to your question without considering the application.

A lot will also depend on the matrix material. Much will also depend on how you intend to prepare the material and what the application is (and what the temperature of application is). Alumina is chemically very stable and is generally not wetted so well by most metals. SiC is chemically less stable (but has good oxidation resistance due to formation of a protective oxide layer). It tends to react when in contact with molten aluminium and at high temperatures when in contact with iron and nickel. So producing the composite will not be easy. There are ways to make Al-SiC composites (via the Duralcan process for example), but recycling by melting is not advisable as reaction will occur to form the hygroscopic Al4C3.

SiC and Al2O3 both are high strength ceramic particles. you may refer below article,

Chapter Study on Squeeze Casting of Aluminum Matrix Composites—A Review

Density of Silicon Carbide particulate is higher than Aluminium Oxide. During the processing of Aluminium based composites, Silicon carbide reinforced settles down while pouring

SiC posses improved wear and thermal properties in addition to fatigue and mechanical strength